[0/4] DST: Distributed storage.

[0/4] DST: Distributed storage.

[Evgeniy Polyakov]

Distributed storage.

I'm pleased to announce the 12'th release of the distributed
storage subsystem (DST).

DST allows to form a storage on top of local and remote nodes
and combine them into linear or mirroring setup, which in
turn can be exported to remote nodes.

Short changelog:
 * new improved mirroring algorithm.
	This algorithm uses sliding window approach for full resync
	and write log for partial resync.
 * fixed number of typos and debug cleanups
 * update inode size when linear algorithm changes the size of the
	storage in run time
 * extended number of sysfs files and documentation for them
 * fixed leak in local export node setup
 * name is 'Dancing with the smoked neutrino' now

Overall list of features of the DST can be found on project's homepage:

http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst

DST is also exported as a git tree available for clone and pull from
http://tservice.net.ru/~s0mbre/archive/dst/dst.git

Interested reader can test DST with 2.6.23 tree too
(it should compile fine, but was not tested).

DST passed all FS tests in LTP with XFS (modulo MAX_LOCK_DEPTH too low bug:
[ 8398.605691] BUG: MAX_LOCK_DEPTH too low!
[ 8398.609641] turning off the locking correctness validator.

this is not DST problem though), but it was not performed with
offline/online nodes.

Thank you.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>

[1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

Distributed storage documentation.

Algorithms used in the system, userspace interfaces
(sysfs dirs and files), design and implementation details
are described here.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


diff --git a/Documentation/dst/algorithms.txt b/Documentation/dst/algorithms.txt
new file mode 100644
index 0000000..1437a6a
--- /dev/null
+++ b/Documentation/dst/algorithms.txt
@@ -0,0 +1,115 @@
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+
+Let's briefly describe how they work.
+
+Linear algorithm.
+Simple approach of concatenating storages into single device with
+increased size is used in this algorithm. Essentially new device
+has size equal to sum of sizes of underlying nodes and nodes are
+placed one after another.
+
+  /----- Node 1 ---\                         /------ Node 3 ----\
+start              end                     start               end
+ |==================|========================|==================|
+ |                start                     end                 |
+ |                  \------- Node 2 ---------/                  |
+ |                                                              |
+start                                                          end
+ \-------------------------- DST storage ----------------------/
+
+			        /\
+			        ||
+			        ||
+
+			   IO operations
+
+			    Figure 1. 
+     3 nodes combined into single storage using linear algorithm.
+
+Mirror algorithm.
+In this algorithms nodes are placed under each other, so when
+operation comes to the first one, it can be mirrored to all
+underlying nodes. In case of reading, actual data is obtained from
+the nearest node - algoritm keeps track of previous operation
+and knows where it was stopped, so that subsequent seek to the 
+start of the new request will take the shortest time.
+Writing is always mirrored to all underlying nodes.
+
+                  IO operations
+                       ||
+                       ||
+                       \/
+
+|---------------- DST storage -------------------|
+|      prev position                             |
+|-------|------------ Node 1 --------------------|
+|                              prev pos          |
+|-------------------- Node 2 -----|--------------|
+|prev pos                                        |
+|---|---------------- Node 3 --------------------|
+
+		Figure 2.
+   3 nodes combined into single storage using mirror algorithm.
+
+Each algorithm must implement number of callbacks,
+which must be registered during initialization time.
+
+struct dst_alg_ops
+{
+	int			(*add_node)(struct dst_node *n);
+	void			(*del_node)(struct dst_node *n);
+	int 			(*remap)(struct dst_request *req);
+	int			(*error)(struct kst_state *state, int err);
+	struct module 		*owner;
+};
+
+@add_node.
+This callback is invoked when new node is being added into the storage,
+but before node is actually added into the storage, so that it could
+be accessed from it. When it is called, all appropriate initialization
+of the underlying device is already completed (system has been connected
+to remote node or got a reference to the local block device). At this
+stage algorithm can add node into private map. 
+It must return zero on success or negative value otherwise.
+
+@del_node.
+This callback is invoked when node is being deleted from the storage,
+i.e. when its reference counter hits zero. It is called before
+any cleaning is performed.
+It must return zero on success or negative value otherwise.
+
+@remap.
+This callback is invoked each time new bio hits the storage.
+Request structure contains BIO itself, pointer to the node, which originally
+stores the whole region under given IO request, and various parameters
+used by storage core to process this block request.
+It must return zero on success or negative value otherwise. It is upto
+this method to call all cleaning if remapping failed, for example it must
+call kst_bio_endio() for given callback in case of error, which in turn
+will call bio_endio(). Note, that dst_request structure provided in this
+callback is allocated on stack, so if there is a need to use it outside
+of the given function, it must be cloned (it will happen automatically
+in state's push callback, but that copy will not be shared by any other
+user).
+
+@error.
+This callback is invoked for each error, which happend when processed
+requests for remote nodes or when talking to remote size
+of the local export node (state contains data related to data
+transfers over the network).
+If this function has fixed given error, it must return 0 or negative
+error value otherwise.
+
+@owner.
+This is module reference counter updated automatically by DST core.
+
+Algorithm must provide its name and above structure to the 
+dst_alloc_alg() function, which will return a reference to the newly
+created algorithm.
+To remove it, one needs to call dst_remove_alg() with given algorithm
+pointer.
diff --git a/Documentation/dst/dst.txt b/Documentation/dst/dst.txt
new file mode 100644
index 0000000..a6ea126
--- /dev/null
+++ b/Documentation/dst/dst.txt
@@ -0,0 +1,69 @@
+Distributed storage. Design and implementation.
+http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst
+
+	     Evgeniy Polyakov
+
+This document is intended to briefly describe design and
+implementation details of the distributed storage project,
+aimed to create ability to group physically and/or logically
+distributed storages into single device.
+
+Main operational unit in the storage is node. Node can represent
+either remote storage, connected to local machine, or local
+device, or storage exported to the outside of the system.
+Here goes small explaination of basic therms.
+
+Local node.
+This node is just a logical link between block device (with given
+major and minor numbers) and structure in the DST hierarchy,
+which represents number of sectors on the area, corresponding to given
+block device. it can be a disk, a device mapper node or stacked
+block device on top of another underlying DST nodes.
+
+Local export node.
+Essentially the same as local node, but it allows to access
+to its data via network. Remote clients can connect to given local 
+export node and read or write blocks according to its size.
+Blocks are then forwarded to underlying local node and processed
+there accordingly to the nature of the local node.
+
+Remote node.
+This type of nodes contain remotely accessible devices. One can think
+about remote nodes as remote disks, which can be connected to
+local system and combined into single storage. Remote nodes
+are presented as number of sectors accessed over the network
+by the local machine, where distributed storage is being formed.
+Remote node allows autoconfiguration - size of the storage and
+checksumming will be requested during node initialization (if remote
+node supports checksumming it will be turned on).
+
+
+Each node or set of them can be formed into single array, which
+in turn becomes a local node, which can be exported further by stacking
+a local export node on top of it.
+
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+One can find more details in Documentation/dst/algorithms.txt file.
+
+Main goal of the distributed storage is to combine remote nodes into
+single device, so each block IO request is being sent over the network
+(contrary requests for local nodes are handled by the gneric block
+layer features). Each network connection has number of variables which
+describe it (socket, list of requests, error handling and so on),
+which form kst_state structure. This network state is added into per-socket
+polling state machine, and can be processed by dedicated thread when
+becomes ready. This system forms asynchronous IO for given block
+requests. If block request can be processed without blocking, then
+no new structures are allocated and async part of the state is not used.
+
+When connection to the remote peer breaks, DST core tries to reconnect
+to failed node and no requests are marked as errorneous, instead
+they live in the queue until reconnectin is established.
+
+Userspace code, setup documentation and examples can be found on project's
+homepage above.
diff --git a/Documentation/dst/sysfs.txt b/Documentation/dst/sysfs.txt
new file mode 100644
index 0000000..63e5c00
--- /dev/null
+++ b/Documentation/dst/sysfs.txt
@@ -0,0 +1,33 @@
+This file describes sysfs files created for each storage.
+
+1. Per-storage files.
+Each storage has its own dir /sysfs/devices/$storage_name,
+which contains following files:
+
+alg - contains name of the algorithm used to created given storage
+name - name of the storage
+nodes - map of the storage (list of nodes and their sizes and starts)
+remove_all_nodes - writable file which allows to remove all nodes from given
+	storage
+n-$start-$cookie - per node directory, where
+	$start - start of the given node in sectors,
+	$cookie - unique node's id used by DST
+
+2. Per-node files.
+Node's files are located in /sysfs/devices/$storage_name/n-$start-$cookie
+directory, described above.
+
+clean - writable file, writing leads to marking node as clean (in sync)
+dirty - writable file, writing leads to marking node as dirty (not in sync)
+resync_size - size of the resync sliding window
+resync_timout - resync requests checking timeout (in milliseconds) of
+	the background worker thread
+state - sync/notsync state of the node in the mirror
+
+flags - flags of the given node
+size - size of the given node in sectors
+start - start of the given node in the storage in sectors
+type - contains type of the node in the following format: $type: $dev
+	where $type is either 'L' or 'R' - local or remote acordingly,
+	and $dev is device name for local node (/dev/sda1 for example)
+	or address of the remote node (192.168.4.81:1025 for example)

[2/4] DST: Core distributed storage files.

[Evgeniy Polyakov]

Core distributed storage files.
Include userspace interfaces, initialization,
block layer bindings and other core functionality.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index b4c8319..ca6592d 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -451,6 +451,8 @@ config ATA_OVER_ETH
 	This driver provides Support for ATA over Ethernet block
 	devices like the Coraid EtherDrive (R) Storage Blade.
 
+source "drivers/block/dst/Kconfig"
+
 source "drivers/s390/block/Kconfig"
 
 endmenu
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index dd88e33..fcf042d 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -29,3 +29,4 @@ obj-$(CONFIG_VIODASD)		+= viodasd.o
 obj-$(CONFIG_BLK_DEV_SX8)	+= sx8.o
 obj-$(CONFIG_BLK_DEV_UB)	+= ub.o
 
+obj-$(CONFIG_DST)		+= dst/
diff --git a/drivers/block/dst/Kconfig b/drivers/block/dst/Kconfig
new file mode 100644
index 0000000..67a7dad
--- /dev/null
+++ b/drivers/block/dst/Kconfig
@@ -0,0 +1,28 @@
+config DST
+	tristate "Distributed storage"
+	depends on NET
+	select CONNECTOR
+	select LIBCRC32C
+	---help---
+	This driver allows to create a distributed storage.
+
+config DST_DEBUG
+	bool "DST debug"
+	depends on DST
+	---help---
+	This option will turn HEAVY debugging of the DST.
+	Turn it on ONLY if you have to debug some really obscure problem.
+
+config DST_ALG_LINEAR
+	tristate "Linear distribution algorithm"
+	depends on DST
+	---help---
+	This module allows to create linear mapping of the nodes
+	in the distributed storage.
+
+config DST_ALG_MIRROR
+	tristate "Mirror distribution algorithm"
+	depends on DST
+	---help---
+	This module allows to create a mirror of the nodes in the
+	distributed storage.
diff --git a/drivers/block/dst/Makefile b/drivers/block/dst/Makefile
new file mode 100644
index 0000000..1400e94
--- /dev/null
+++ b/drivers/block/dst/Makefile
@@ -0,0 +1,6 @@
+obj-$(CONFIG_DST) += dst.o
+
+dst-y := dcore.o kst.o
+
+obj-$(CONFIG_DST_ALG_LINEAR) += alg_linear.o
+obj-$(CONFIG_DST_ALG_MIRROR) += alg_mirror.o
diff --git a/drivers/block/dst/dcore.c b/drivers/block/dst/dcore.c
new file mode 100644
index 0000000..423e7b2
--- /dev/null
+++ b/drivers/block/dst/dcore.c
@@ -0,0 +1,1622 @@
+/*
+ * 2007+ Copyright (c) Evgeniy Polyakov <johnpol@2ka.mipt.ru>
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/connector.h>
+#include <linux/socket.h>
+#include <linux/dst.h>
+#include <linux/device.h>
+#include <linux/in.h>
+#include <linux/in6.h>
+#include <linux/buffer_head.h>
+
+#include <net/sock.h>
+
+static LIST_HEAD(dst_storage_list);
+static LIST_HEAD(dst_alg_list);
+static DEFINE_MUTEX(dst_storage_lock);
+static DEFINE_MUTEX(dst_alg_lock);
+static int dst_major;
+static struct kst_worker *kst_main_worker;
+static struct cb_id cn_dst_id = { CN_DST_IDX, CN_DST_VAL };
+
+struct kmem_cache *dst_request_cache;
+
+static char dst_name[] = "Dancing with the smoked neutrino";
+
+/*
+ * DST sysfs tree. For device called 'storage' which is formed
+ * on top of two nodes this looks like this:
+ *
+ * /sys/devices/storage/
+ * /sys/devices/storage/alg : alg_linear
+ * /sys/devices/storage/n-800/type : R: 192.168.4.80:1025
+ * /sys/devices/storage/n-800/size : 800
+ * /sys/devices/storage/n-800/start : 800
+ * /sys/devices/storage/n-800/clean
+ * /sys/devices/storage/n-800/dirty
+ * /sys/devices/storage/n-0/type : R: 192.168.4.81:1025
+ * /sys/devices/storage/n-0/size : 800
+ * /sys/devices/storage/n-0/start : 0
+ * /sys/devices/storage/n-0/clean
+ * /sys/devices/storage/n-0/dirty
+ * /sys/devices/storage/remove_all_nodes
+ * /sys/devices/storage/nodes : sectors (start [size]): 0 [800] | 800 [800]
+ * /sys/devices/storage/name : storage
+ */
+
+static int dst_dev_match(struct device *dev, struct device_driver *drv)
+{
+	return 1;
+}
+
+static void dst_dev_release(struct device *dev)
+{
+}
+
+static struct bus_type dst_dev_bus_type = {
+	.name 		= "dst",
+	.match 		= &dst_dev_match,
+};
+
+static struct device dst_dev = {
+	.bus 		= &dst_dev_bus_type,
+	.release 	= &dst_dev_release
+};
+
+static void dst_node_release(struct device *dev)
+{
+}
+
+static struct device dst_node_dev = {
+	.release 	= &dst_node_release
+};
+
+static void dst_free_alg(struct dst_alg *alg)
+{
+	kfree(alg);
+}
+
+/*
+ * Algorithm is never freed directly,
+ * since its module reference counter is increased
+ * by storage when it is created - just like network protocols.
+ */
+static inline void dst_put_alg(struct dst_alg *alg)
+{
+	module_put(alg->ops->owner);
+	if (atomic_dec_and_test(&alg->refcnt))
+		dst_free_alg(alg);
+}
+
+static void dst_remove_disk(struct dst_storage *st)
+{
+	put_disk(st->disk);
+	blk_cleanup_queue(st->queue);
+}
+
+static void dst_free_storage(struct dst_storage *st)
+{
+	BUG_ON(rb_first(&st->tree_root) != NULL);
+
+	dst_remove_disk(st);
+	dst_put_alg(st->alg);
+	kfree(st);
+}
+
+static inline void dst_put_storage(struct dst_storage *st)
+{
+	if (atomic_dec_and_test(&st->refcnt))
+		dst_free_storage(st);
+}
+
+static struct bio_set *dst_bio_set;
+
+static void dst_destructor(struct bio *bio)
+{
+	bio_free(bio, dst_bio_set);
+}
+
+/*
+ * Internal callback for local requests (i.e. for local disk),
+ * which are splitted between nodes (part with local node destination
+ * ends up with this ->bi_end_io() callback).
+ */
+static int dst_end_io(struct bio *bio, unsigned int size, int err)
+{
+	struct bio *orig_bio = bio->bi_private;
+
+	if (bio->bi_size)
+		return 0;
+
+	dprintk("%s: bio: %p, orig_bio: %p, size: %u, orig_size: %u.\n",
+		__func__, bio, orig_bio, size, orig_bio->bi_size);
+
+	bio_endio(orig_bio, size, 0);
+	bio_put(bio);
+	return 0;
+}
+
+/*
+ * This function sends processing request down to block layer (for local node)
+ * or to network state machine (for remote node).
+ */
+static int dst_node_push(struct dst_request *req)
+{
+	int err = 0;
+	struct dst_node *n = req->node;
+
+	if (n->bdev) {
+		struct bio *bio = req->bio;
+
+		dprintk("%s: start: %llu, num: %d, idx: %d, offset: %u, "
+				"size: %llu, bi_idx: %d, bi_vcnt: %d.\n",
+			__func__, req->start, req->num, req->idx,
+			req->offset, req->size,	bio->bi_idx, bio->bi_vcnt);
+
+		if (likely(bio->bi_idx == req->idx &&
+					bio->bi_vcnt == req->num)) {
+			bio->bi_bdev = n->bdev;
+			bio->bi_sector = req->start;
+		} else {
+			struct bio *clone = bio_alloc_bioset(GFP_NOIO,
+					bio->bi_max_vecs, dst_bio_set);
+			struct bio_vec *bv;
+
+			err = -ENOMEM;
+			if (!clone)
+				goto out_put;
+
+			__bio_clone(clone, bio);
+
+			bv = bio_iovec_idx(clone, req->idx);
+			bv->bv_offset += req->offset;
+			clone->bi_idx = req->idx;
+			clone->bi_vcnt = req->num;
+			clone->bi_bdev = n->bdev;
+			clone->bi_sector = req->start;
+			clone->bi_destructor = dst_destructor;
+			clone->bi_private = bio;
+			clone->bi_size = req->orig_size;
+			clone->bi_end_io = &dst_end_io;
+			req->bio = clone;
+
+			dprintk("%s: start: %llu, num: %d, idx: %d, "
+				"offset: %u, size: %llu, "
+				"bi_idx: %d, bi_vcnt: %d, req: %p, bio: %p.\n",
+				__func__, req->start, req->num, req->idx,
+				req->offset, req->size,
+				clone->bi_idx, clone->bi_vcnt, req, req->bio);
+
+		}
+	}
+
+	err = n->st->alg->ops->remap(req);
+
+out_put:
+	dst_node_put(n);
+	return err;
+}
+
+/*
+ * This function is invoked from block layer request processing function,
+ * its task is to remap block request to different nodes.
+ */
+static int dst_remap(struct dst_storage *st, struct bio *bio)
+{
+	struct dst_node *n;
+	int err = -EINVAL, i, cnt;
+	unsigned int bio_sectors = bio->bi_size>>9;
+	struct bio_vec *bv;
+	struct dst_request req;
+	u64 rest_in_node, start, total_size;
+
+	mutex_lock(&st->tree_lock);
+	n = dst_storage_tree_search(st, bio->bi_sector);
+	mutex_unlock(&st->tree_lock);
+
+	if (!n) {
+		dprintk("%s: failed to find a node for bio: %p, "
+				"sector: %llu.\n",
+				__func__, bio, (u64)bio->bi_sector);
+		return -ENODEV;
+	}
+
+	dprintk("%s: bio: %llu-%llu, dev: %llu-%llu, in sectors.\n",
+			__func__, (u64)bio->bi_sector, (u64)bio->bi_sector+bio_sectors,
+			n->start, n->start+n->size);
+
+	memset(&req, 0, sizeof(struct dst_request));
+
+	start = bio->bi_sector;
+	total_size = bio->bi_size;
+
+	dst_fill_request(&req, bio, start - n->start, n, &kst_bio_endio);
+
+	/*
+	 * Common fast path - block request does not cross
+	 * boundaries between nodes.
+	 */
+	if (likely(bio->bi_sector + bio_sectors <= n->start + n->size))
+		return dst_node_push(&req);
+
+	req.size = 0;
+	req.idx = 0;
+	req.num = 1;
+
+	cnt = bio->bi_vcnt;
+
+	rest_in_node = to_bytes(n->size - req.start);
+
+	for (i = 0; i < cnt; ++i) {
+		bv = bio_iovec_idx(bio, i);
+
+		if (req.size + bv->bv_len >= rest_in_node) {
+			unsigned int diff = req.size + bv->bv_len -
+				rest_in_node;
+
+			req.size += bv->bv_len - diff;
+			req.start = start - n->start;
+			req.orig_size = req.size;
+			req.bio = bio;
+			req.bio_endio = &kst_bio_endio;
+
+			dprintk("%s: split: start: %llu/%llu, size: %llu, "
+					"total_size: %llu, diff: %u, idx: %d, "
+					"num: %d, bv_len: %u, bv_offset: %u.\n",
+					__func__, start, req.start, req.size,
+					total_size, diff, req.idx, req.num,
+					bv->bv_len, bv->bv_offset);
+
+			err = dst_node_push(&req);
+			if (err)
+				break;
+
+			total_size -= req.orig_size;
+
+			if (!total_size)
+				break;
+
+			start += to_sector(req.orig_size);
+
+			req.flags = (test_bit(DST_NODE_FROZEN, &n->flags))?
+				DST_REQ_ALWAYS_QUEUE:0;
+			req.orig_size = req.size = diff;
+
+			if (diff) {
+				req.offset = bv->bv_len - diff;
+				req.idx = req.num - 1;
+			} else {
+				req.idx = req.num;
+				req.offset = 0;
+			}
+
+			dprintk("%s: next: start: %llu, size: %llu, "
+				"total_size: %llu, diff: %u, idx: %d, "
+				"num: %d, offset: %u, bv_len: %u, "
+				"bv_offset: %u.\n",
+				__func__, start, req.size, total_size, diff,
+				req.idx, req.num, req.offset,
+				bv->bv_len, bv->bv_offset);
+
+			mutex_lock(&st->tree_lock);
+			n = dst_storage_tree_search(st, start);
+			mutex_unlock(&st->tree_lock);
+
+			if (!n) {
+				err = -ENODEV;
+				dprintk("%s: failed to find a split node for "
+				  "bio: %p, sector: %llu, start: %llu.\n",
+						__func__, bio, (u64)bio->bi_sector,
+						req.start);
+				break;
+			}
+
+			req.state = n->state;
+			req.node = n;
+			req.start = start - n->start;
+			rest_in_node = to_bytes(n->size - req.start);
+
+			dprintk("%s: req.start: %llu, start: %llu, "
+					"dev_start: %llu, dev_size: %llu, "
+					"rest_in_node: %llu.\n",
+				__func__, req.start, start, n->start,
+				n->size, rest_in_node);
+		} else {
+			req.size += bv->bv_len;
+			req.num++;
+		}
+	}
+
+	dprintk("%s: last request: start: %llu, size: %llu, "
+			"total_size: %llu.\n", __func__,
+			req.start, req.size, total_size);
+	if (total_size) {
+		req.orig_size = req.size;
+		req.bio = bio;
+		req.bio_endio = &kst_bio_endio;
+
+		dprintk("%s: last: start: %llu/%llu, size: %llu, "
+				"total_size: %llu, idx: %d, num: %d.\n",
+			__func__, start, req.start, req.size,
+			total_size, req.idx, req.num);
+
+		err = dst_node_push(&req);
+		if (!err) {
+			total_size -= req.orig_size;
+
+			BUG_ON(total_size != 0);
+		}
+	}
+
+	dprintk("%s: end bio: %p, err: %d.\n", __func__, bio, err);
+	return err;
+}
+
+/*
+ * Distributed storage erquest processing function.
+ * It calls algorithm spcific remapping code only.
+ */
+static int dst_request(struct request_queue *q, struct bio *bio)
+{
+	struct dst_storage *st = q->queuedata;
+	int err;
+
+	dprintk("\n%s: start: st: %p, bio: %p, cnt: %u.\n",
+			__func__, st, bio, bio->bi_vcnt);
+
+	err = dst_remap(st, bio);
+	if (err)
+		bio_endio(bio, bio->bi_size, err);
+
+	dprintk("%s: end: st: %p, bio: %p, err: %d.\n",
+			__func__, st, bio, err);
+	return 0;
+}
+
+static void dst_unplug(struct request_queue *q)
+{
+}
+
+static int dst_flush(struct request_queue *q, struct gendisk *disk, sector_t *sec)
+{
+	return 0;
+}
+
+static int dst_blk_open(struct inode *inode, struct file *file)
+{
+	struct dst_storage *st = inode->i_bdev->bd_disk->private_data;
+
+	atomic_inc(&st->refcnt);
+	return 0;
+}
+
+static int dst_blk_release(struct inode *inode, struct file *file)
+{
+	struct dst_storage *st = inode->i_bdev->bd_disk->private_data;
+
+	dst_put_storage(st);
+	return 0;
+}
+
+static struct block_device_operations dst_blk_ops = {
+	.open = &dst_blk_open,
+	.release = &dst_blk_release,
+	.owner = THIS_MODULE,
+};
+
+/*
+ * Block layer binding - disk is created when array is fully configured
+ * by userspace request.
+ */
+static int dst_create_disk(struct dst_storage *st)
+{
+	int err = -ENOMEM;
+
+	st->queue = blk_alloc_queue(GFP_KERNEL);
+	if (!st->queue)
+		goto err_out_exit;
+
+	st->queue->queuedata = st;
+	blk_queue_make_request(st->queue, dst_request);
+	blk_queue_bounce_limit(st->queue, BLK_BOUNCE_ANY);
+	st->queue->unplug_fn = dst_unplug;
+	st->queue->issue_flush_fn = dst_flush;
+
+	err = -EINVAL;
+	st->disk = alloc_disk(1);
+	if (!st->disk)
+		goto err_out_free_queue;
+
+	st->disk->major = dst_major;
+	st->disk->first_minor = (((unsigned long)st->disk) ^
+		(((unsigned long)st->disk) >> 31)) & 0xff;
+	st->disk->fops = &dst_blk_ops;
+	st->disk->queue = st->queue;
+	st->disk->private_data = st;
+	snprintf(st->disk->disk_name, sizeof(st->disk->disk_name),
+			"dst-%s-%d", st->name, st->disk->first_minor);
+
+	return 0;
+
+err_out_free_queue:
+	blk_cleanup_queue(st->queue);
+err_out_exit:
+	return err;
+}
+
+/*
+ * Shows node name in sysfs.
+ */
+static ssize_t dst_name_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dst_storage *st = container_of(dev, struct dst_storage, device);
+
+	return sprintf(buf, "%s\n", st->name);
+}
+
+static void dst_remove_all_nodes(struct dst_storage *st)
+{
+	struct dst_node *n, *node, *tmp;
+	struct rb_node *rb_node;
+
+	mutex_lock(&st->tree_lock);
+	while ((rb_node = rb_first(&st->tree_root)) != NULL) {
+		n = rb_entry(rb_node, struct dst_node, tree_node);
+		rb_erase(&n->tree_node, &st->tree_root);
+		if (!n->shared_head && atomic_read(&n->shared_num)) {
+			list_for_each_entry_safe(node, tmp, &n->shared, shared) {
+				list_del(&node->shared);
+				atomic_dec(&n->shared_num);
+				dst_node_put(node->shared_head);
+				node->shared_head = NULL;
+				dst_node_put(node);
+			}
+		}
+		dst_node_put(n);
+	}
+	mutex_unlock(&st->tree_lock);
+}
+
+/*
+ * Shows node layout in syfs.
+ */
+static ssize_t dst_nodes_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dst_storage *st = container_of(dev, struct dst_storage, device);
+	int size = PAGE_CACHE_SIZE, sz;
+	struct dst_node *n;
+	struct rb_node *rb_node;
+
+	sz = sprintf(buf, "sectors (start [size]): ");
+	size -= sz;
+	buf += sz;
+
+	mutex_lock(&st->tree_lock);
+	for (rb_node = rb_first(&st->tree_root); rb_node;
+			rb_node = rb_next(rb_node)) {
+		n = rb_entry(rb_node, struct dst_node, tree_node);
+		if (size < 32)
+			break;
+		sz = sprintf(buf, "%llu [%llu]", n->start, n->size);
+		buf += sz;
+		size -= sz;
+
+		if (!rb_next(rb_node))
+			break;
+
+		sz = sprintf(buf, " | ");
+		buf += sz;
+		size -= sz;
+	}
+	mutex_unlock(&st->tree_lock);
+	size -= sprintf(buf, "\n");
+	return PAGE_CACHE_SIZE - size;
+}
+
+/*
+ * Algorithm currently being used by given storage.
+ */
+static ssize_t dst_alg_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dst_storage *st = container_of(dev, struct dst_storage, device);
+	return sprintf(buf, "%s\n", st->alg->name);
+}
+
+/*
+ * Writing to this sysfs file allows to remove all nodes
+ * and storage itself automatically.
+ */
+static ssize_t dst_remove_nodes(struct device *dev,
+		struct device_attribute *attr,
+		const char *buf, size_t count)
+{
+	struct dst_storage *st = container_of(dev, struct dst_storage, device);
+	dst_remove_all_nodes(st);
+	return count;
+}
+
+static DEVICE_ATTR(name, 0444, dst_name_show, NULL);
+static DEVICE_ATTR(nodes, 0444, dst_nodes_show, NULL);
+static DEVICE_ATTR(alg, 0444, dst_alg_show, NULL);
+static DEVICE_ATTR(remove_all_nodes, 0644, NULL, dst_remove_nodes);
+
+static int dst_create_storage_attributes(struct dst_storage *st)
+{
+	int err;
+
+	err = device_create_file(&st->device, &dev_attr_name);
+	err = device_create_file(&st->device, &dev_attr_nodes);
+	err = device_create_file(&st->device, &dev_attr_alg);
+	err = device_create_file(&st->device, &dev_attr_remove_all_nodes);
+	return 0;
+}
+
+static void dst_remove_storage_attributes(struct dst_storage *st)
+{
+	device_remove_file(&st->device, &dev_attr_name);
+	device_remove_file(&st->device, &dev_attr_nodes);
+	device_remove_file(&st->device, &dev_attr_alg);
+	device_remove_file(&st->device, &dev_attr_remove_all_nodes);
+}
+
+static void dst_storage_sysfs_exit(struct dst_storage *st)
+{
+	dst_remove_storage_attributes(st);
+	device_unregister(&st->device);
+}
+
+static int dst_storage_sysfs_init(struct dst_storage *st)
+{
+	int err;
+
+	memcpy(&st->device, &dst_dev, sizeof(struct device));
+	snprintf(st->device.bus_id, sizeof(st->device.bus_id), "%s", st->name);
+
+	err = device_register(&st->device);
+	if (err) {
+		dprintk(KERN_ERR "Failed to register dst device %s, err: %d.\n",
+			st->name, err);
+		goto err_out_exit;
+	}
+
+	dst_create_storage_attributes(st);
+
+	return 0;
+
+err_out_exit:
+	return err;
+}
+
+/*
+ * This functions shows size and start of the appropriate node.
+ * Both are in sectors.
+ */
+static ssize_t dst_show_start(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+
+	return sprintf(buf, "%llu\n", n->start);
+}
+
+static ssize_t dst_show_size(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+
+	return sprintf(buf, "%llu\n", n->size);
+}
+
+/*
+ * This function shows node's flags in hex.
+ */
+static ssize_t dst_show_flags(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+
+	return sprintf(buf, "0x%lx\n", n->flags);
+}
+
+/*
+ * Shows type of the remote node - device major/minor number
+ * for local nodes and address (af_inet ipv4/ipv6 only) for remote nodes.
+ */
+static ssize_t dst_show_type(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+	struct sockaddr addr;
+	struct socket *sock;
+	int addrlen;
+
+	if (!n->state && !n->bdev)
+		return 0;
+
+	if (n->bdev)
+		return sprintf(buf, "L: %d:%d\n",
+				MAJOR(n->bdev->bd_dev), MINOR(n->bdev->bd_dev));
+
+	sock = n->state->socket;
+	if (sock->ops->getname(sock, &addr, &addrlen, 2))
+		return 0;
+
+	if (sock->ops->family == AF_INET) {
+		struct sockaddr_in *sin = (struct sockaddr_in *)&addr;
+		return sprintf(buf, "R: %u.%u.%u.%u:%d\n",
+			NIPQUAD(sin->sin_addr.s_addr), ntohs(sin->sin_port));
+	} else if (sock->ops->family == AF_INET6) {
+		struct sockaddr_in6 *sin = (struct sockaddr_in6 *)&addr;
+		return sprintf(buf,
+			"R: %04x:%04x:%04x:%04x:%04x:%04x:%04x:%04x:%d\n",
+			NIP6(sin->sin6_addr), ntohs(sin->sin6_port));
+	}
+	return 0;
+}
+
+static struct device_attribute dst_node_attrs[] = {
+	__ATTR(start, 0444, dst_show_start, NULL),
+	__ATTR(size, 0444, dst_show_size, NULL),
+	__ATTR(flags, 0444, dst_show_flags, NULL),
+	__ATTR(type, 0444, dst_show_type, NULL),
+};
+
+static int dst_create_node_attributes(struct dst_node *n)
+{
+	int err, i;
+
+	for (i=0; i<ARRAY_SIZE(dst_node_attrs); ++i)
+		err = device_create_file(&n->device,
+				&dst_node_attrs[i]);
+	return 0;
+}
+
+static void dst_remove_node_attributes(struct dst_node *n)
+{
+	int i;
+
+	for (i=0; i<ARRAY_SIZE(dst_node_attrs); ++i)
+		device_remove_file(&n->device,
+				&dst_node_attrs[i]);
+}
+
+static void dst_node_sysfs_exit(struct dst_node *n)
+{
+	if (n->device.parent == &n->st->device) {
+		dst_remove_node_attributes(n);
+		device_unregister(&n->device);
+		n->device.parent = NULL;
+	}
+}
+
+static int dst_node_sysfs_init(struct dst_node *n)
+{
+	int err;
+
+	memcpy(&n->device, &dst_node_dev, sizeof(struct device));
+
+	n->device.parent = &n->st->device;
+
+	snprintf(n->device.bus_id, sizeof(n->device.bus_id),
+			"n-%llu-%p", n->start, n);
+	err = device_register(&n->device);
+	if (err) {
+		dprintk(KERN_ERR "Failed to register node, err: %d.\n", err);
+		goto err_out_exit;
+	}
+
+	dst_create_node_attributes(n);
+
+	return 0;
+
+err_out_exit:
+	n->device.parent = NULL;
+	return err;
+}
+
+/*
+ * Gets a reference for given storage, if
+ * storage with given name and algorithm being used
+ * does not exist it is created.
+ */
+static struct dst_storage *dst_get_storage(char *name, char *aname, int alloc)
+{
+	struct dst_storage *st, *rst = NULL;
+	int err;
+	struct dst_alg *alg;
+
+	mutex_lock(&dst_storage_lock);
+	list_for_each_entry(st, &dst_storage_list, entry) {
+		if (!strcmp(name, st->name) && !strcmp(st->alg->name, aname)) {
+			rst = st;
+			atomic_inc(&st->refcnt);
+			break;
+		}
+	}
+
+	if (rst || !alloc) {
+		mutex_unlock(&dst_storage_lock);
+		return rst;
+	}
+
+	st = kzalloc(sizeof(struct dst_storage), GFP_KERNEL);
+	if (!st) {
+		mutex_unlock(&dst_storage_lock);
+		return NULL;
+	}
+
+	mutex_init(&st->tree_lock);
+	/*
+	 * One for storage itself,
+	 * another one for attached node below.
+	 */
+	atomic_set(&st->refcnt, 2);
+	snprintf(st->name, DST_NAMELEN, "%s", name);
+	st->tree_root.rb_node = NULL;
+
+	err = dst_storage_sysfs_init(st);
+	if (err)
+		goto err_out_free;
+
+	err = dst_create_disk(st);
+	if (err)
+		goto err_out_sysfs_exit;
+
+	mutex_lock(&dst_alg_lock);
+	list_for_each_entry(alg, &dst_alg_list, entry) {
+		if (!strcmp(alg->name, aname)) {
+			atomic_inc(&alg->refcnt);
+			try_module_get(alg->ops->owner);
+			st->alg = alg;
+			break;
+		}
+	}
+	mutex_unlock(&dst_alg_lock);
+
+	if (!st->alg)
+		goto err_out_disk_remove;
+
+	list_add_tail(&st->entry, &dst_storage_list);
+	mutex_unlock(&dst_storage_lock);
+
+	return st;
+
+err_out_disk_remove:
+	dst_remove_disk(st);
+err_out_sysfs_exit:
+	dst_storage_sysfs_exit(st);
+err_out_free:
+	mutex_unlock(&dst_storage_lock);
+	kfree(st);
+	return NULL;
+}
+
+/*
+ * Allows to allocate and add new algorithm by external modules.
+ */
+struct dst_alg *dst_alloc_alg(char *name, struct dst_alg_ops *ops)
+{
+	struct dst_alg *alg;
+
+	alg = kzalloc(sizeof(struct dst_alg), GFP_KERNEL);
+	if (!alg)
+		return NULL;
+	snprintf(alg->name, DST_NAMELEN, "%s", name);
+	atomic_set(&alg->refcnt, 1);
+	alg->ops = ops;
+
+	mutex_lock(&dst_alg_lock);
+	list_add_tail(&alg->entry, &dst_alg_list);
+	mutex_unlock(&dst_alg_lock);
+
+	return alg;
+}
+EXPORT_SYMBOL_GPL(dst_alloc_alg);
+
+/*
+ * Removing algorithm from main list of supported algorithms.
+ */
+void dst_remove_alg(struct dst_alg *alg)
+{
+	mutex_lock(&dst_alg_lock);
+	list_del_init(&alg->entry);
+	mutex_unlock(&dst_alg_lock);
+
+	dst_put_alg(alg);
+}
+EXPORT_SYMBOL_GPL(dst_remove_alg);
+
+static void dst_cleanup_node(struct dst_node *n)
+{
+	struct dst_storage *st = n->st;
+
+	if (n->shared_head) {
+		mutex_lock(&st->tree_lock);
+		list_del(&n->shared);
+		mutex_unlock(&st->tree_lock);
+
+		atomic_dec(&n->shared_head->refcnt);
+		dst_node_put(n->shared_head);
+		n->shared_head = NULL;
+	}
+
+	if (n->cleanup)
+		n->cleanup(n);
+	dst_node_sysfs_exit(n);
+	n->st->alg->ops->del_node(n);
+	kfree(n);
+}
+
+/*
+ * This can deadlock if called under st->tree_lock being held,
+ * so take care to only call this when reference counter can not
+ * hit zero and thus start node freeing.
+ */
+void dst_node_put(struct dst_node *n)
+{
+	if (atomic_dec_and_test(&n->refcnt)) {
+		struct dst_storage *st = n->st;
+
+		dprintk("%s: freeing node: %p, start: %llu, size: %llu, "
+			"shared_head: %p, shared_num: %d, flags: %lx.\n",
+			__func__, n, n->start, n->size,
+			n->shared_head, atomic_read(&n->shared_num),
+			n->flags);
+
+		dst_cleanup_node(n);
+		dst_put_storage(st);
+	}
+}
+EXPORT_SYMBOL_GPL(dst_node_put);
+
+static inline int dst_compare_id(struct dst_node *old, u64 new)
+{
+	if (old->start + old->size <= new)
+		return 1;
+	if (old->start > new)
+		return -1;
+	return 0;
+}
+
+/*
+ * Tree of of the nodes, which form the storage.
+ * Tree is indexed via start of the node and its size.
+ * Comparison function above.
+ */
+struct dst_node *dst_storage_tree_search(struct dst_storage *st, u64 start)
+{
+	struct rb_node *n = st->tree_root.rb_node;
+	struct dst_node *dn;
+	int cmp;
+
+	while (n) {
+		dn = rb_entry(n, struct dst_node, tree_node);
+
+		cmp = dst_compare_id(dn, start);
+		dprintk("%s: tree: %llu-%llu, new: %llu.\n",
+			__func__, dn->start, dn->start+dn->size, start);
+		if (cmp < 0)
+			n = n->rb_left;
+		else if (cmp > 0)
+			n = n->rb_right;
+		else {
+			return dst_node_get(dn);
+		}
+	}
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(dst_storage_tree_search);
+
+/*
+ * This function allows to remove a node with given start address
+ * from the storage.
+ */
+static struct dst_node *dst_storage_tree_del(struct dst_storage *st, u64 start)
+{
+	struct dst_node *n = dst_storage_tree_search(st, start);
+
+	if (!n)
+		return NULL;
+
+	rb_erase(&n->tree_node, &st->tree_root);
+	dst_node_put(n);
+	return n;
+}
+
+/*
+ * This function allows to add given node to the storage.
+ * Returns -EEXIST if the same area is already covered by another node.
+ * This is return must be checked for redundancy algorithms.
+ */
+static struct dst_node *dst_storage_tree_add(struct dst_node *new,
+		struct dst_storage *st)
+{
+	struct rb_node **n = &st->tree_root.rb_node, *parent = NULL;
+	struct dst_node *dn;
+	int cmp;
+
+	while (*n) {
+		parent = *n;
+		dn = rb_entry(parent, struct dst_node, tree_node);
+
+		cmp = dst_compare_id(dn, new->start);
+		dprintk("%s: tree: %llu-%llu, new: %llu.\n",
+				__func__, dn->start, dn->start+dn->size,
+				new->start);
+		if (cmp < 0)
+			n = &parent->rb_left;
+		else if (cmp > 0)
+			n = &parent->rb_right;
+		else {
+			return dn;
+		}
+	}
+
+	rb_link_node(&new->tree_node, parent, n);
+	rb_insert_color(&new->tree_node, &st->tree_root);
+
+	return NULL;
+}
+
+/*
+ * This function finds devices major/minor numbers for given pathname.
+ */
+static int dst_lookup_device(const char *path, dev_t *dev)
+{
+	int err;
+	struct nameidata nd;
+	struct inode *inode;
+
+	err = path_lookup(path, LOOKUP_FOLLOW, &nd);
+	if (err)
+		return err;
+
+	inode = nd.dentry->d_inode;
+	if (!inode) {
+		err = -ENOENT;
+		goto out;
+	}
+
+	if (!S_ISBLK(inode->i_mode)) {
+		err = -ENOTBLK;
+		goto out;
+	}
+
+	*dev = inode->i_rdev;
+
+out:
+	path_release(&nd);
+	return err;
+}
+
+/*
+ * Cleanup routings for local, local exporting and remote nodes.
+ */
+static void dst_cleanup_remote(struct dst_node *n)
+{
+	if (n->state) {
+		kst_state_exit(n->state);
+		n->state = NULL;
+	}
+}
+
+static void dst_cleanup_local(struct dst_node *n)
+{
+	if (n->bdev) {
+		sync_blockdev(n->bdev);
+		blkdev_put(n->bdev);
+		n->bdev = NULL;
+	}
+}
+
+static void dst_cleanup_local_export(struct dst_node *n)
+{
+	dst_cleanup_local(n);
+	dst_cleanup_remote(n);
+}
+
+/*
+ * Header receiving function - may block.
+ */
+int dst_data_recv_header(struct socket *sock,
+		struct dst_remote_request *r, int block)
+{
+	struct msghdr msg;
+	struct kvec iov;
+
+	iov.iov_base = r;
+	iov.iov_len = sizeof(struct dst_remote_request);
+
+	msg.msg_iov = (struct iovec *)&iov;
+	msg.msg_iovlen = 1;
+	msg.msg_name = NULL;
+	msg.msg_namelen = 0;
+	msg.msg_control = NULL;
+	msg.msg_controllen = 0;
+	msg.msg_flags = (block)?MSG_WAITALL:MSG_DONTWAIT | MSG_NOSIGNAL;
+
+	return kernel_recvmsg(sock, &msg, &iov, 1, iov.iov_len,
+			msg.msg_flags);
+}
+
+/*
+ * Header sending function - may block.
+ */
+int dst_data_send_header(struct socket *sock,
+		struct dst_remote_request *r)
+{
+	struct msghdr msg;
+	struct kvec iov;
+
+	iov.iov_base = r;
+	iov.iov_len = sizeof(struct dst_remote_request);
+
+	msg.msg_iov = (struct iovec *)&iov;
+	msg.msg_iovlen = 1;
+	msg.msg_name = NULL;
+	msg.msg_namelen = 0;
+	msg.msg_control = NULL;
+	msg.msg_controllen = 0;
+	msg.msg_flags = MSG_WAITALL | MSG_NOSIGNAL;
+
+	return kernel_sendmsg(sock, &msg, &iov, 1, iov.iov_len);
+}
+
+static inline void dst_node_set_size(struct dst_node *n, u64 size)
+{
+	if (n->size)
+		n->size = min(size, n->size);
+	else
+		n->size = size;
+}
+
+/*
+ * Setup routings for local, local exporting and remote nodes.
+ */
+static int dst_setup_local(struct dst_node *n, struct dst_ctl *ctl,
+		struct dst_local_ctl *l)
+{
+	dev_t dev;
+	int err;
+
+	err = dst_lookup_device(l->name, &dev);
+	if (err)
+		return err;
+
+	n->bdev = open_by_devnum(dev, FMODE_READ|FMODE_WRITE);
+	if (!n->bdev)
+		return -ENODEV;
+
+	dst_node_set_size(n, to_sector(n->bdev->bd_inode->i_size));
+
+	return 0;
+}
+
+static int dst_setup_local_export(struct dst_node *n, struct dst_ctl *ctl,
+		struct dst_le_template *tmp)
+{
+	int err;
+
+	err = dst_setup_local(n, ctl, &tmp->le->lctl);
+	if (err)
+		goto err_out_exit;
+
+	n->state = kst_listener_state_init(n, tmp);
+	if (IS_ERR(n->state)) {
+		err = PTR_ERR(n->state);
+		goto err_out_cleanup;
+	}
+
+	return 0;
+
+err_out_cleanup:
+	dst_cleanup_local(n);
+err_out_exit:
+	return err;
+}
+
+static int dst_request_remote_config(struct dst_node *n, struct socket *sock)
+{
+	struct dst_remote_request cfg;
+	int err = -EINVAL;
+
+	memset(&cfg, 0, sizeof(struct dst_remote_request));
+	cfg.cmd = cpu_to_be32(DST_REMOTE_CFG);
+
+	dprintk("%s: sending header.\n", __func__);
+	err = dst_data_send_header(sock, &cfg);
+	if (err != sizeof(struct dst_remote_request))
+		goto out;
+
+	dprintk("%s: receiving header.\n", __func__);
+	err = dst_data_recv_header(sock, &cfg, 1);
+	if (err != sizeof(struct dst_remote_request))
+		goto out;
+
+	err = -EINVAL;
+	dprintk("%s: checking result: cmd: %d, size reported: %llu, csum is supported: %u.\n",
+			__func__, be32_to_cpu(cfg.cmd), be64_to_cpu(cfg.sector), !!cfg.csum);
+	if (be32_to_cpu(cfg.cmd) != DST_REMOTE_CFG)
+		goto out;
+
+	err = 0;
+	dst_node_set_size(n, be64_to_cpu(cfg.sector));
+
+	if (cfg.csum)
+		__set_bit(DST_NODE_USE_CSUM, &n->flags);
+	else
+		__clear_bit(DST_NODE_USE_CSUM, &n->flags);
+
+out:
+	dprintk("%s: n: %p, err: %d.\n", __func__, n, err);
+	return err;
+}
+
+static int dst_setup_remote(struct dst_node *n, struct dst_ctl *ctl,
+		struct dst_remote_ctl *r)
+{
+	int err;
+	struct socket *sock;
+
+	err = sock_create(r->addr.sa_family, r->type, r->proto, &sock);
+	if (err < 0)
+		goto err_out_exit;
+
+	sock->sk->sk_sndtimeo = sock->sk->sk_rcvtimeo =
+		msecs_to_jiffies(DST_DEFAULT_TIMEO);
+
+	err = sock->ops->connect(sock, (struct sockaddr *)&r->addr,
+			r->addr.sa_data_len, 0);
+	if (err)
+		goto err_out_destroy;
+
+	err = dst_request_remote_config(n, sock);
+	if (err)
+		goto err_out_destroy;
+
+	n->state = kst_data_state_init(n, sock);
+	if (IS_ERR(n->state)) {
+		err = PTR_ERR(n->state);
+		goto err_out_destroy;
+	}
+
+	return 0;
+
+err_out_destroy:
+	sock_release(sock);
+err_out_exit:
+
+	dprintk("%s: n: %p, err: %d.\n", __func__, n, err);
+	return err;
+}
+
+/*
+ * This function inserts node into storage.
+ */
+static int dst_insert_node(struct dst_node *n)
+{
+	int err;
+	struct dst_storage *st = n->st;
+	struct dst_node *dn;
+
+	err = st->alg->ops->add_node(n);
+	if (err)
+		goto err_out_exit;
+
+	err = dst_node_sysfs_init(n);
+	if (err)
+		goto err_out_remove_node;
+
+	mutex_lock(&st->tree_lock);
+	dn = dst_storage_tree_add(n, st);
+	if (dn) {
+		err = -EINVAL;
+		dn->size = st->disk_size;
+		if (dn->start == n->start)
+			err = 0;
+	}
+	mutex_unlock(&st->tree_lock);
+	if (err)
+		goto err_out_sysfs_exit;
+
+	if (n->priv_callback)
+		n->priv_callback(n);
+
+	return 0;
+
+err_out_sysfs_exit:
+	dst_node_sysfs_exit(n);
+err_out_remove_node:
+	st->alg->ops->del_node(n);
+err_out_exit:
+	return err;
+}
+
+static struct dst_node *dst_alloc_node(struct dst_ctl *ctl,
+		void (*cleanup)(struct dst_node *))
+{
+	struct dst_storage *st;
+	struct dst_node *n;
+
+	st = dst_get_storage(ctl->st, ctl->alg, 1);
+	if (!st)
+		goto err_out_exit;
+
+	n = kzalloc(sizeof(struct dst_node), GFP_KERNEL);
+	if (!n)
+		goto err_out_put_storage;
+
+	if (ctl->flags & DST_CTL_USE_CSUM)
+		__set_bit(DST_NODE_USE_CSUM, &n->flags);
+
+	n->w = kst_main_worker;
+	n->st = st;
+	n->cleanup = cleanup;
+	n->start = ctl->start;
+	n->size = ctl->size;
+	INIT_LIST_HEAD(&n->shared);
+	n->shared_head = NULL;
+	atomic_set(&n->shared_num, 0);
+	atomic_set(&n->refcnt, 1);
+
+	return n;
+
+err_out_put_storage:
+	mutex_lock(&dst_storage_lock);
+	list_del_init(&st->entry);
+	mutex_unlock(&dst_storage_lock);
+
+	dst_put_storage(st);
+err_out_exit:
+	return NULL;
+}
+
+/*
+ * Control callback for userspace commands to setup
+ * different nodes and start/stop array.
+ */
+static int dst_add_remote(struct dst_ctl *ctl, void *data, unsigned int len)
+{
+	struct dst_node *n;
+	int err;
+	struct dst_remote_ctl *rctl = data;
+
+	if (len != sizeof(struct dst_remote_ctl))
+		return -EINVAL;
+
+	n = dst_alloc_node(ctl, &dst_cleanup_remote);
+	if (!n)
+		return -ENOMEM;
+
+	err = dst_setup_remote(n, ctl, rctl);
+	if (err < 0)
+		goto err_out_free;
+
+	err = dst_insert_node(n);
+	if (err)
+		goto err_out_cleanup;
+
+	return 0;
+
+err_out_cleanup:
+	if (n->cleanup)
+		n->cleanup(n);
+err_out_free:
+	dst_put_storage(n->st);
+	kfree(n);
+	return err;
+}
+
+static int dst_add_local_export(struct dst_ctl *ctl, void *data, unsigned int len)
+{
+	struct dst_node *n;
+	int err;
+	struct dst_le_template tmp;
+
+	if (len < sizeof(struct dst_local_export_ctl))
+		return -EINVAL;
+
+	tmp.le = data;
+
+	len -= sizeof(struct dst_local_export_ctl);
+	data += sizeof(struct dst_local_export_ctl);
+
+	if (len != tmp.le->secure_attr_num * sizeof(struct dst_secure_user))
+		return -EINVAL;
+
+	tmp.data = data;
+
+	n = dst_alloc_node(ctl, &dst_cleanup_local_export);
+	if (!n)
+		return -EINVAL;
+
+	err = dst_setup_local_export(n, ctl, &tmp);
+	if (err < 0)
+		goto err_out_free;
+
+	err = dst_insert_node(n);
+	if (err)
+		goto err_out_cleanup;
+
+	return 0;
+
+err_out_cleanup:
+	if (n->cleanup)
+		n->cleanup(n);
+err_out_free:
+	dst_put_storage(n->st);
+	kfree(n);
+	return err;
+}
+
+static int dst_add_local(struct dst_ctl *ctl, void *data, unsigned int len)
+{
+	struct dst_node *n;
+	int err;
+	struct dst_local_ctl *lctl = data;
+
+	if (len != sizeof(struct dst_local_ctl))
+		return -EINVAL;
+
+	n = dst_alloc_node(ctl, &dst_cleanup_local);
+	if (!n)
+		return -EINVAL;
+
+	err = dst_setup_local(n, ctl, lctl);
+	if (err < 0)
+		goto err_out_free;
+
+	err = dst_insert_node(n);
+	if (err)
+		goto err_out_cleanup;
+
+	return 0;
+
+err_out_cleanup:
+	if (n->cleanup)
+		n->cleanup(n);
+err_out_free:
+	dst_put_storage(n->st);
+	kfree(n);
+	return err;
+}
+
+static int dst_del_node(struct dst_ctl *ctl, void *data, unsigned int len)
+{
+	struct dst_node *n;
+	struct dst_storage *st;
+	int err = -ENODEV;
+
+	if (len)
+		return -EINVAL;
+
+	st = dst_get_storage(ctl->st, ctl->alg, 0);
+	if (!st)
+		goto err_out_exit;
+
+	mutex_lock(&st->tree_lock);
+	n = dst_storage_tree_del(st, ctl->start);
+	mutex_unlock(&st->tree_lock);
+	if (!n)
+		goto err_out_put;
+
+	dst_node_put(n);
+	dst_put_storage(st);
+
+	return 0;
+
+err_out_put:
+	dst_put_storage(st);
+err_out_exit:
+	return err;
+}
+
+static int dst_start_storage(struct dst_ctl *ctl, void *data, unsigned int len)
+{
+	struct dst_storage *st;
+	int err = -ENXIO;
+
+	if (len)
+		return -EINVAL;
+
+	st = dst_get_storage(ctl->st, ctl->alg, 0);
+	if (!st)
+		return -ENODEV;
+
+	mutex_lock(&st->tree_lock);
+	if (!(st->flags & DST_ST_STARTED) && st->disk_size) {
+		set_capacity(st->disk, st->disk_size);
+		add_disk(st->disk);
+		st->flags |= DST_ST_STARTED;
+		printk("%s: STARTED name: '%s', st: %p, disk_size: %llu.\n",
+				__func__, st->name, st, st->disk_size);
+		err = 0;
+	}
+	mutex_unlock(&st->tree_lock);
+
+	dst_put_storage(st);
+
+	return err;
+}
+
+static int dst_stop_storage(struct dst_ctl *ctl, void *data, unsigned int len)
+{
+	struct dst_storage *st;
+
+	if (len)
+		return -EINVAL;
+
+	st = dst_get_storage(ctl->st, ctl->alg, 0);
+	if (!st)
+		return -ENODEV;
+
+	printk("%s: STOPPED storage: %s.\n", __func__, st->name);
+
+	dst_storage_sysfs_exit(st);
+
+	mutex_lock(&dst_storage_lock);
+	list_del_init(&st->entry);
+	mutex_unlock(&dst_storage_lock);
+
+	if (st->flags & DST_ST_STARTED)
+		del_gendisk(st->disk);
+
+	dst_remove_all_nodes(st);
+	dst_put_storage(st); /* One reference got above */
+	dst_put_storage(st); /* Another reference set during initialization */
+
+	return 0;
+}
+
+typedef int (*dst_command_func)(struct dst_ctl *ctl, void *data, unsigned int len);
+
+/*
+ * List of userspace commands.
+ */
+static dst_command_func dst_commands[] = {
+	[DST_ADD_REMOTE] = &dst_add_remote,
+	[DST_ADD_LOCAL] = &dst_add_local,
+	[DST_ADD_LOCAL_EXPORT] = &dst_add_local_export,
+	[DST_DEL_NODE] = &dst_del_node,
+	[DST_START_STORAGE] = &dst_start_storage,
+	[DST_STOP_STORAGE] = &dst_stop_storage,
+};
+
+/*
+ * Configuration parser.
+ */
+static void cn_dst_callback(void *data)
+{
+	struct dst_ctl *ctl;
+	struct cn_msg *msg = data;
+	int err;
+	struct dst_ctl_ack *ack;
+
+	if (msg->len < sizeof(struct dst_ctl)) {
+		err = -EBADMSG;
+		goto out;
+	}
+
+	ctl = (struct dst_ctl *)msg->data;
+
+	if (ctl->cmd >= DST_CMD_MAX) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	err = dst_commands[ctl->cmd](ctl, msg->data + sizeof(struct dst_ctl),
+			msg->len - sizeof(struct dst_ctl));
+
+out:
+	ack = kmalloc(sizeof(struct dst_ctl_ack), GFP_KERNEL);
+	if (!ack)
+		return;
+
+	memcpy(&ack->msg, msg, sizeof(struct cn_msg));
+
+	ack->msg.ack = msg->ack + 1;
+	ack->msg.len = sizeof(struct dst_ctl_ack) - sizeof(struct cn_msg);
+
+	ack->error = err;
+
+	cn_netlink_send(&ack->msg, 0, GFP_KERNEL);
+	kfree(ack);
+}
+
+static int dst_sysfs_init(void)
+{
+	return bus_register(&dst_dev_bus_type);
+}
+
+static void dst_sysfs_exit(void)
+{
+	bus_unregister(&dst_dev_bus_type);
+}
+
+static int __init dst_sys_init(void)
+{
+	int err = -ENOMEM;
+
+	dst_request_cache = kmem_cache_create("dst", sizeof(struct dst_request),
+				       0, 0, NULL, NULL);
+	if (!dst_request_cache)
+		return -ENOMEM;
+
+	dst_bio_set = bioset_create(32, 32);
+	if (!dst_bio_set)
+		goto err_out_destroy;
+
+	err = register_blkdev(dst_major, DST_NAME);
+	if (err < 0)
+		goto err_out_destroy_bioset;
+	if (err)
+		dst_major = err;
+
+	err = dst_sysfs_init();
+	if (err)
+		goto err_out_unregister;
+
+	kst_main_worker = kst_worker_init(0);
+	if (IS_ERR(kst_main_worker)) {
+		err = PTR_ERR(kst_main_worker);
+		goto err_out_sysfs_exit;
+	}
+
+	err = cn_add_callback(&cn_dst_id, "DST", cn_dst_callback);
+	if (err)
+		goto err_out_worker_exit;
+
+	printk(KERN_INFO "Distributed storage, '%s' release.\n", dst_name);
+
+	return 0;
+
+err_out_worker_exit:
+	kst_worker_exit(kst_main_worker);
+err_out_sysfs_exit:
+	dst_sysfs_exit();
+err_out_unregister:
+	unregister_blkdev(dst_major, DST_NAME);
+err_out_destroy_bioset:
+	bioset_free(dst_bio_set);
+err_out_destroy:
+	kmem_cache_destroy(dst_request_cache);
+	return err;
+}
+
+static void __exit dst_sys_exit(void)
+{
+	cn_del_callback(&cn_dst_id);
+	dst_sysfs_exit();
+	unregister_blkdev(dst_major, DST_NAME);
+	kst_exit_all();
+	bioset_free(dst_bio_set);
+	kmem_cache_destroy(dst_request_cache);
+}
+
+module_init(dst_sys_init);
+module_exit(dst_sys_exit);
+
+MODULE_DESCRIPTION("Distributed storage");
+MODULE_AUTHOR("Evgeniy Polyakov <johnpol@2ka.mipt.ru>");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/connector.h b/include/linux/connector.h
index 10eb56b..9e67d58 100644
--- a/include/linux/connector.h
+++ b/include/linux/connector.h
@@ -36,9 +36,11 @@
 #define CN_VAL_CIFS                     0x1
 #define CN_W1_IDX			0x3	/* w1 communication */
 #define CN_W1_VAL			0x1
+#define CN_DST_IDX			0x4	/* Distributed storage */
+#define CN_DST_VAL			0x1
 
 
-#define CN_NETLINK_USERS		4
+#define CN_NETLINK_USERS		5
 
 /*
  * Maximum connector's message size.
diff --git a/include/linux/dst.h b/include/linux/dst.h
new file mode 100644
index 0000000..df92d54
--- /dev/null
+++ b/include/linux/dst.h
@@ -0,0 +1,404 @@
+/*
+ * 2007+ Copyright (c) Evgeniy Polyakov <johnpol@2ka.mipt.ru>
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef __DST_H
+#define __DST_H
+
+#include <linux/types.h>
+#include <linux/connector.h>
+
+#define DST_NAMELEN		32
+#define DST_NAME		"dst"
+#define DST_IOCTL		0xba
+
+enum {
+	DST_DEL_NODE	= 0,	/* Remove node with given id from storage */
+	DST_ADD_REMOTE,		/* Add remote node with given id to the storage */
+	DST_ADD_LOCAL,		/* Add local node with given id to the storage */
+	DST_ADD_LOCAL_EXPORT,	/* Add local node with given id to the storage to be exported and used by remote peers */
+	DST_START_STORAGE,	/* Array is ready and storage can be started, if there will be new nodes
+				 * added to the storage, they will be checked against existing size and
+				 * probably be dropped (for example in mirror format when new node has smaller
+				 * size than array created) or inserted.
+				 */
+	DST_STOP_STORAGE,	/* Remove array and all nodes. */
+	DST_CMD_MAX
+};
+
+#define DST_CTL_FLAGS_REMOTE	(1<<0)
+#define DST_CTL_FLAGS_EXPORT	(1<<1)
+#define DST_CTL_USE_CSUM	(1<<2)
+
+struct dst_ctl
+{
+	char			st[DST_NAMELEN];
+	char			alg[DST_NAMELEN];
+	__u32			flags, cmd;
+	__u64			start, size;
+};
+
+struct dst_ctl_ack
+{
+	struct cn_msg		msg;
+	int			error;
+	int			unused[3];
+};
+
+struct dst_local_ctl
+{
+	char			name[DST_NAMELEN];
+};
+
+#define SADDR_MAX_DATA	128
+
+struct saddr {
+	unsigned short		sa_family;			/* address family, AF_xxx	*/
+	char			sa_data[SADDR_MAX_DATA];	/* 14 bytes of protocol address	*/
+	unsigned short		sa_data_len;			/* Number of bytes used in sa_data */
+};
+
+struct dst_remote_ctl
+{
+	__u16			type;
+	__u16			proto;
+	struct saddr		addr;
+};
+
+#define DST_PERM_READ		(1<<0)
+#define DST_PERM_WRITE		(1<<1)
+
+/*
+ * Right now it is simple model, where each remote address
+ * is assigned to set of permissions it is allowed to perform.
+ * In real world block device does not know anything but
+ * reading and writing, so it should be more than enough.
+ */
+struct dst_secure_user
+{
+	unsigned int		permissions;
+	unsigned short		check_offset;
+	struct saddr		addr;
+};
+
+struct dst_local_export_ctl
+{
+	__u32			backlog;
+	int			secure_attr_num;
+	struct dst_local_ctl	lctl;
+	struct dst_remote_ctl	rctl;
+};
+
+enum {
+	DST_REMOTE_CFG		= 1, 		/* Request remote configuration */
+	DST_WRITE,				/* Writing */
+	DST_READ,				/* Reading */
+	DST_NCMD_MAX,
+};
+
+struct dst_remote_request
+{
+	__u32			cmd;
+	__u32			csum;
+	__u32			size;
+	__u32			offset;
+	__u64			sector;
+};
+
+#ifdef __KERNEL__
+
+#include <linux/rbtree.h>
+#include <linux/net.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/mempool.h>
+#include <linux/device.h>
+#include <linux/crc32c.h>
+
+//#define CONFIG_DST_DEBUG
+
+#ifdef CONFIG_DST_DEBUG
+#define dprintk(f, a...) printk(KERN_NOTICE f, ##a)
+#else
+static inline void __attribute__ ((format (printf, 1, 2))) dprintk(const char * fmt, ...) {}
+#endif
+
+struct kst_worker
+{
+	struct list_head	entry;
+
+	struct list_head	state_list;
+	struct mutex		state_mutex;
+
+	struct list_head	ready_list;
+	spinlock_t		ready_lock;
+
+	mempool_t		*req_pool;
+
+	struct task_struct	*thread;
+
+	wait_queue_head_t 	wait;
+
+	int			id;
+};
+
+struct kst_state;
+struct dst_node;
+
+#define DST_REQ_HEADER_SENT	(1<<0)
+#define DST_REQ_EXPORT		(1<<1)
+#define DST_REQ_EXPORT_WRITE	(1<<2)
+#define DST_REQ_EXPORT_READ	(1<<3)
+#define DST_REQ_ALWAYS_QUEUE	(1<<4)
+#define DST_REQ_CHEKSUM_RECV	(1<<5)
+#define DST_REQ_CHECK_QUEUE	(1<<6)
+
+struct dst_request
+{
+	struct list_head	request_list_entry;
+	struct bio		*bio;
+	struct kst_state 	*state;
+	struct dst_node 	*node;
+
+	u32			tmp_csum, tmp_offset;
+
+	u32			flags;
+
+	u32			offset;
+	int			idx, num;
+
+	int 			(*callback)(struct dst_request *dst,
+						unsigned int revents);
+	void			(*bio_endio)(struct dst_request *dst, 
+						int err);
+
+	atomic_t		refcnt;
+	void			*priv;
+
+	u64			size, orig_size, start;
+};
+
+struct kst_state_ops
+{
+	int 		(*init)(struct kst_state *, void *);
+	int 		(*push)(struct dst_request *req);
+	int		(*ready)(struct kst_state *);
+	int		(*recovery)(struct kst_state *, int err);
+	void 		(*exit)(struct kst_state *);
+};
+
+struct kst_state
+{
+	struct list_head	entry;
+	struct list_head	ready_entry;
+
+	wait_queue_t 		wait;
+	wait_queue_head_t 	*whead;
+
+	struct dst_node		*node;
+	struct socket		*socket;
+
+	u32			permissions;
+
+	struct mutex		request_lock;
+	struct list_head	request_list;
+
+	struct kst_state_ops	*ops;
+};
+
+#define DST_DEFAULT_TIMEO	2000
+
+struct dst_storage;
+
+struct dst_alg_ops
+{
+	int			(*add_node)(struct dst_node *n);
+	void			(*del_node)(struct dst_node *n);
+	int 			(*remap)(struct dst_request *req);
+	int			(*error)(struct kst_state *state, int err);
+	struct module 		*owner;
+};
+
+struct dst_alg
+{
+	struct list_head	entry;
+	char			name[DST_NAMELEN];
+	atomic_t		refcnt;
+	struct dst_alg_ops	*ops;
+};
+
+#define DST_ST_STARTED		(1<<0)
+
+struct dst_storage
+{
+	struct list_head	entry;
+	char			name[DST_NAMELEN];
+	struct dst_alg		*alg;
+	atomic_t		refcnt;
+	struct mutex		tree_lock;
+	struct rb_root		tree_root;
+
+	struct request_queue	*queue;
+	struct gendisk		*disk;
+
+	long			flags;
+	u64			disk_size;
+
+	struct device		device;
+};
+
+#define DST_NODE_FROZEN		0
+#define DST_NODE_NOTSYNC	1
+#define DST_NODE_USE_CSUM	2
+
+struct dst_node
+{
+	struct rb_node		tree_node;
+
+	struct list_head	shared;
+	struct dst_node		*shared_head;
+
+	struct block_device 	*bdev;
+	struct dst_storage	*st;
+	struct kst_state	*state;
+	struct kst_worker	*w;
+
+	atomic_t		refcnt;
+	atomic_t		shared_num;
+
+	void			(*cleanup)(struct dst_node *);
+
+	long			flags;
+
+	u64			start, size;
+
+	void			(*priv_callback)(struct dst_node *);
+	void			*priv;
+
+	struct device		device;
+};
+
+struct dst_le_template
+{
+	struct dst_local_export_ctl	*le;
+	void 				*data;
+};
+
+struct dst_secure
+{
+	struct list_head	sec_entry;
+	struct dst_secure_user	sec;
+};
+
+void kst_state_exit(struct kst_state *st);
+
+struct kst_worker *kst_worker_init(int id);
+void kst_worker_exit(struct kst_worker *w);
+
+struct kst_state *kst_listener_state_init(struct dst_node *node,
+		struct dst_le_template *tmp);
+struct kst_state *kst_data_state_init(struct dst_node *node,
+		struct socket *newsock);
+
+void kst_wake(struct kst_state *st);
+
+void kst_exit_all(void);
+
+struct dst_alg *dst_alloc_alg(char *name, struct dst_alg_ops *ops);
+void dst_remove_alg(struct dst_alg *alg);
+
+struct dst_node *dst_storage_tree_search(struct dst_storage *st, u64 start);
+
+void dst_node_put(struct dst_node *n);
+
+static inline struct dst_node *dst_node_get(struct dst_node *n)
+{
+	atomic_inc(&n->refcnt);
+	return n;
+}
+
+struct dst_request *dst_clone_request(struct dst_request *req, mempool_t *pool);
+void dst_free_request(struct dst_request *req);
+
+void kst_complete_req(struct dst_request *req, int err);
+void kst_bio_endio(struct dst_request *req, int err);
+void kst_del_req(struct dst_request *req);
+int kst_enqueue_req(struct kst_state *st, struct dst_request *req);
+
+int kst_data_callback(struct dst_request *req, unsigned int revents);
+
+extern struct kmem_cache *dst_request_cache;
+
+static inline sector_t to_sector(unsigned long long n)
+{
+	return (n >> 9);
+}
+
+static inline unsigned long to_bytes(sector_t n)
+{
+	return (n << 9);
+}
+
+/*
+ * Checks state's permissions.
+ * Returns -EPERM if check failed.
+ */
+static inline int kst_check_permissions(struct kst_state *st, struct bio *bio)
+{
+	if ((bio_rw(bio) == WRITE) && !(st->permissions & DST_PERM_WRITE))
+		return -EPERM;
+
+	return 0;
+}
+
+static inline __u32 dst_csum_data(unsigned char *d, unsigned int size)
+{
+	return crc32c_le(0, d, size);
+}
+
+static inline void kst_convert_header(struct dst_remote_request *r)
+{
+	r->cmd = be32_to_cpu(r->cmd);
+	r->sector = be64_to_cpu(r->sector);
+	r->offset = be32_to_cpu(r->offset);
+	r->size = be32_to_cpu(r->size);
+	r->csum = be32_to_cpu(r->csum);
+}
+
+extern int dst_data_send_header(struct socket *sock,
+		struct dst_remote_request *r);
+extern int dst_data_recv_header(struct socket *sock,
+		struct dst_remote_request *r, int block);
+
+static inline void dst_fill_request(struct dst_request *req, struct bio *bio,
+	u64 start, struct dst_node *n, void (*req_bio_endio)(struct dst_request *req, int err))
+{
+	req->flags = (test_bit(DST_NODE_FROZEN, &n->flags))?
+				DST_REQ_ALWAYS_QUEUE:0;
+	req->start = start;
+	req->offset = 0;
+	req->state = n->state;
+	req->node = n;
+	req->bio = bio;
+
+	req->size = bio->bi_size;
+	req->orig_size = bio->bi_size;
+	req->idx = bio->bi_idx;
+	req->num = bio->bi_vcnt;
+
+	req->bio_endio = req_bio_endio;
+}
+
+#endif /* __KERNEL__ */
+#endif /* __DST_H */

[3/4] DST: Network state machine.

[Evgeniy Polyakov]

Network state machine.

Includes network async processing state machine and related tasks.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


diff --git a/drivers/block/dst/kst.c b/drivers/block/dst/kst.c
new file mode 100644
index 0000000..6d92014
--- /dev/null
+++ b/drivers/block/dst/kst.c
@@ -0,0 +1,1515 @@
+/*
+ * 2007+ Copyright (c) Evgeniy Polyakov <johnpol@2ka.mipt.ru>
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/socket.h>
+#include <linux/kthread.h>
+#include <linux/net.h>
+#include <linux/in.h>
+#include <linux/poll.h>
+#include <linux/bio.h>
+#include <linux/dst.h>
+
+#include <net/sock.h>
+
+struct kst_poll_helper
+{
+	poll_table 		pt;
+	struct kst_state	*st;
+};
+
+static LIST_HEAD(kst_worker_list);
+static DEFINE_MUTEX(kst_worker_mutex);
+
+/*
+ * This function creates bound socket for local export node.
+ */
+static int kst_sock_create(struct kst_state *st, struct saddr *addr,
+		int type, int proto, int backlog)
+{
+	int err;
+
+	err = sock_create(addr->sa_family, type, proto, &st->socket);
+	if (err)
+		goto err_out_exit;
+
+	err = st->socket->ops->bind(st->socket, (struct sockaddr *)addr,
+			addr->sa_data_len);
+
+	err = st->socket->ops->listen(st->socket, backlog);
+	if (err)
+		goto err_out_release;
+
+	st->socket->sk->sk_allocation = GFP_NOIO;
+
+	return 0;
+
+err_out_release:
+	sock_release(st->socket);
+err_out_exit:
+	return err;
+}
+
+static void kst_sock_release(struct kst_state *st)
+{
+	if (st->socket) {
+		sock_release(st->socket);
+		st->socket = NULL;
+	}
+}
+
+void kst_wake(struct kst_state *st)
+{
+	if (st) {
+		struct kst_worker *w = st->node->w;
+		unsigned long flags;
+
+		spin_lock_irqsave(&w->ready_lock, flags);
+		if (list_empty(&st->ready_entry))
+			list_add_tail(&st->ready_entry, &w->ready_list);
+		spin_unlock_irqrestore(&w->ready_lock, flags);
+
+		wake_up(&w->wait);
+	}
+}
+EXPORT_SYMBOL_GPL(kst_wake);
+
+/*
+ * Polling machinery.
+ */
+static int kst_state_wake_callback(wait_queue_t *wait, unsigned mode,
+		int sync, void *key)
+{
+	struct kst_state *st = container_of(wait, struct kst_state, wait);
+	kst_wake(st);
+	return 1;
+}
+
+static void kst_queue_func(struct file *file, wait_queue_head_t *whead,
+				 poll_table *pt)
+{
+	struct kst_state *st = container_of(pt, struct kst_poll_helper, pt)->st;
+
+	st->whead = whead;
+	init_waitqueue_func_entry(&st->wait, kst_state_wake_callback);
+	add_wait_queue(whead, &st->wait);
+}
+
+static void kst_poll_exit(struct kst_state *st)
+{
+	if (st->whead) {
+		remove_wait_queue(st->whead, &st->wait);
+		st->whead = NULL;
+	}
+}
+
+/*
+ * This function removes request from state tree and ordering list.
+ */
+void kst_del_req(struct dst_request *req)
+{
+	list_del_init(&req->request_list_entry);
+}
+EXPORT_SYMBOL_GPL(kst_del_req);
+
+static struct dst_request *kst_req_first(struct kst_state *st)
+{
+	struct dst_request *req = NULL;
+
+	if (!list_empty(&st->request_list))
+		req = list_entry(st->request_list.next, struct dst_request,
+				request_list_entry);
+	return req;
+}
+
+/*
+ * This function dequeues first request from the queue and tree.
+ */
+static struct dst_request *kst_dequeue_req(struct kst_state *st)
+{
+	struct dst_request *req;
+
+	mutex_lock(&st->request_lock);
+	req = kst_req_first(st);
+	if (req)
+		kst_del_req(req);
+	mutex_unlock(&st->request_lock);
+	return req;
+}
+
+/*
+ * This function enqueues request into tree, indexed by start of the request,
+ * and also puts request into ordered queue.
+ */
+int kst_enqueue_req(struct kst_state *st, struct dst_request *req)
+{
+	if (unlikely(req->flags & DST_REQ_CHECK_QUEUE)) {
+		struct dst_request *r;
+
+		list_for_each_entry(r, &st->request_list, request_list_entry) {
+			if (bio_rw(r->bio) != bio_rw(req->bio))
+				continue;
+
+			if (r->start >= req->start + req->size)
+				continue;
+
+			if (r->start + r->size <= req->start)
+				continue;
+
+			return -EEXIST;
+		}
+	}
+
+	list_add_tail(&req->request_list_entry, &st->request_list);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kst_enqueue_req);
+
+/*
+ * BIOs for local exporting node are freed via this function.
+ */
+static void kst_export_put_bio(struct bio *bio)
+{
+	int i;
+	struct bio_vec *bv;
+
+	dprintk("%s: bio: %p, size: %u, idx: %d, num: %d, req: %p.\n",
+			__func__, bio, bio->bi_size, bio->bi_idx,
+			bio->bi_vcnt, bio->bi_private);
+
+	bio_for_each_segment(bv, bio, i)
+		__free_page(bv->bv_page);
+	bio_put(bio);
+}
+
+/*
+ * This is a generic request completion function for requests,
+ * queued for async processing.
+ * If it is local export node, state machine is different,
+ * see details below.
+ */
+void kst_complete_req(struct dst_request *req, int err)
+{
+	dprintk("%s: bio: %p, req: %p, size: %llu, orig_size: %llu, "
+			"bi_size: %u, err: %d, flags: %u.\n",
+			__func__, req->bio, req, req->size, req->orig_size,
+			req->bio->bi_size, err, req->flags);
+
+	if (req->flags & DST_REQ_EXPORT) {
+		if (err || !(req->flags & DST_REQ_EXPORT_WRITE)) {
+			req->bio_endio(req, err);
+			goto out;
+		}
+
+		req->bio->bi_rw = WRITE;
+		generic_make_request(req->bio);
+	} else {
+		req->bio_endio(req, err);
+	}
+out:
+	dst_free_request(req);
+}
+EXPORT_SYMBOL_GPL(kst_complete_req);
+
+static void kst_flush_requests(struct kst_state *st)
+{
+	struct dst_request *req;
+
+	while ((req = kst_dequeue_req(st)) != NULL)
+		kst_complete_req(req, -EIO);
+}
+
+static int kst_poll_init(struct kst_state *st)
+{
+	struct kst_poll_helper ph;
+
+	ph.st = st;
+	init_poll_funcptr(&ph.pt, &kst_queue_func);
+
+	st->socket->ops->poll(NULL, st->socket, &ph.pt);
+	return 0;
+}
+
+/*
+ * Main state creation function.
+ * It creates new state according to given operations
+ * and links it into worker structure and node.
+ */
+static struct kst_state *kst_state_init(struct dst_node *node,
+		unsigned int permissions,
+		struct kst_state_ops *ops, void *data)
+{
+	struct kst_state *st;
+	int err;
+
+	st = kzalloc(sizeof(struct kst_state), GFP_KERNEL);
+	if (!st)
+		return ERR_PTR(-ENOMEM);
+
+	st->permissions = permissions;
+	st->node = node;
+	st->ops = ops;
+	INIT_LIST_HEAD(&st->ready_entry);
+	INIT_LIST_HEAD(&st->entry);
+	INIT_LIST_HEAD(&st->request_list);
+	mutex_init(&st->request_lock);
+
+	err = st->ops->init(st, data);
+	if (err)
+		goto err_out_free;
+	mutex_lock(&node->w->state_mutex);
+	list_add_tail(&st->entry, &node->w->state_list);
+	mutex_unlock(&node->w->state_mutex);
+
+	kst_wake(st);
+
+	return st;
+
+err_out_free:
+	kfree(st);
+	return ERR_PTR(err);
+}
+
+/*
+ * This function is called when node is removed,
+ * or when state is destroyed for connected to local exporting
+ * node client.
+ */
+void kst_state_exit(struct kst_state *st)
+{
+	struct kst_worker *w = st->node->w;
+
+	mutex_lock(&w->state_mutex);
+	list_del_init(&st->entry);
+	mutex_unlock(&w->state_mutex);
+
+	st->ops->exit(st);
+
+	if (st == st->node->state)
+		st->node->state = NULL;
+
+	kfree(st);
+}
+
+static int kst_error(struct kst_state *st, int err)
+{
+	if ((err == -ECONNRESET || err == -EPIPE) && st->ops->recovery)
+		err = st->ops->recovery(st, err);
+
+	return st->node->st->alg->ops->error(st, err);
+}
+
+/*
+ * This is main state processing function.
+ * It tries to complete request and invoke appropriate
+ * callbacks in case of errors or successfull operation finish.
+ */
+static int kst_thread_process_state(struct kst_state *st)
+{
+	int err, empty;
+	unsigned int revents;
+	struct dst_request *req, *tmp;
+
+	mutex_lock(&st->request_lock);
+	if (st->ops->ready) {
+		err = st->ops->ready(st);
+		if (err) {
+			mutex_unlock(&st->request_lock);
+			if (err < 0)
+				kst_state_exit(st);
+			return err;
+		}
+	}
+
+	err = 0;
+	empty = 1;
+	req = NULL;
+	list_for_each_entry_safe(req, tmp, &st->request_list, request_list_entry) {
+		empty = 0;
+		revents = st->socket->ops->poll(st->socket->file,
+				st->socket, NULL);
+		if (!revents)
+			break;
+		err = req->callback(req, revents);
+		if (req->size && !err)
+			err = 1;
+
+		if (err < 0 || !req->size) {
+			if (!req->size)
+				err = 0;
+			kst_del_req(req);
+			kst_complete_req(req, err);
+		}
+
+		if (err)
+			break;
+	}
+
+	dprintk("%s: broke the loop: err: %d, list_empty: %d.\n",
+			__func__, err, list_empty(&st->request_list));
+	mutex_unlock(&st->request_lock);
+
+	if (err < 0) {
+		dprintk("%s: req: %p, err: %d, st: %p, node->state: %p.\n",
+			__func__, req, err, st, st->node->state);
+
+		if (st != st->node->state) {
+			/*
+			 * Accepted client has state not related to storage
+			 * node, so it must be freed explicitely.
+			 * We do not try to fix clients connections to local
+			 * export nodes, just drop the client.
+			 */
+
+			kst_state_exit(st);
+			return err;
+		}
+
+		err = kst_error(st, err);
+		if (err)
+			return err;
+
+		kst_wake(st);
+	}
+
+	if (list_empty(&st->request_list) && !empty)
+		kst_wake(st);
+
+	return err;
+}
+
+/*
+ * Main worker thread - one per storage.
+ */
+static int kst_thread_func(void *data)
+{
+	struct kst_worker *w = data;
+	struct kst_state *st;
+	unsigned long flags;
+	int err = 0;
+
+	while (!kthread_should_stop()) {
+		wait_event_interruptible_timeout(w->wait,
+			(!list_empty(&w->ready_list) && !list_empty(&w->state_list)) ||
+			kthread_should_stop(), HZ);
+		st = NULL;
+		spin_lock_irqsave(&w->ready_lock, flags);
+		if (!list_empty(&w->ready_list)) {
+			st = list_entry(w->ready_list.next, struct kst_state,
+				ready_entry);
+			list_del_init(&st->ready_entry);
+		}
+		spin_unlock_irqrestore(&w->ready_lock, flags);
+
+		if (!st)
+			continue;
+
+		err = kst_thread_process_state(st);
+	}
+
+	return err;
+}
+
+/*
+ * Worker initialization - this object will host andprocess all states,
+ * which in turn host requests for remote targets.
+ */
+struct kst_worker *kst_worker_init(int id)
+{
+	struct kst_worker *w;
+	int err;
+
+	w = kzalloc(sizeof(struct kst_worker), GFP_KERNEL);
+	if (!w)
+		return ERR_PTR(-ENOMEM);
+
+	w->id = id;
+	init_waitqueue_head(&w->wait);
+	spin_lock_init(&w->ready_lock);
+	mutex_init(&w->state_mutex);
+
+	INIT_LIST_HEAD(&w->ready_list);
+	INIT_LIST_HEAD(&w->state_list);
+
+	w->req_pool = mempool_create_slab_pool(256, dst_request_cache);
+	if (!w->req_pool) {
+		err = -ENOMEM;
+		goto err_out_free;
+	}
+
+	w->thread = kthread_run(&kst_thread_func, w, "kst%d", w->id);
+	if (IS_ERR(w->thread)) {
+		err = PTR_ERR(w->thread);
+		goto err_out_destroy;
+	}
+
+	mutex_lock(&kst_worker_mutex);
+	list_add_tail(&w->entry, &kst_worker_list);
+	mutex_unlock(&kst_worker_mutex);
+
+	return w;
+
+err_out_destroy:
+	mempool_destroy(w->req_pool);
+err_out_free:
+	kfree(w);
+	return ERR_PTR(err);
+}
+
+void kst_worker_exit(struct kst_worker *w)
+{
+	struct kst_state *st, *n;
+
+	mutex_lock(&kst_worker_mutex);
+	list_del(&w->entry);
+	mutex_unlock(&kst_worker_mutex);
+
+	kthread_stop(w->thread);
+
+	list_for_each_entry_safe(st, n, &w->state_list, entry) {
+		kst_state_exit(st);
+	}
+
+	mempool_destroy(w->req_pool);
+	kfree(w);
+}
+
+/*
+ * Common state exit callback.
+ * Removes itself from worker's list of states,
+ * releases socket and flushes all requests.
+ */
+static void kst_common_exit(struct kst_state *st)
+{
+	unsigned long flags;
+	struct kst_worker *w = st->node->w;
+
+	kst_poll_exit(st);
+
+	spin_lock_irqsave(&w->ready_lock, flags);
+	list_del_init(&st->ready_entry);
+	spin_unlock_irqrestore(&w->ready_lock, flags);
+
+	kst_flush_requests(st);
+	kst_sock_release(st);
+}
+
+/*
+ * Listen socket contains security attributes in request_list,
+ * so it can not be flushed via usual way.
+ */
+static void kst_listen_flush(struct kst_state *st)
+{
+	struct dst_secure *s, *tmp;
+
+	list_for_each_entry_safe(s, tmp, &st->request_list, sec_entry) {
+		list_del(&s->sec_entry);
+		kfree(s);
+	}
+}
+
+static void kst_listen_exit(struct kst_state *st)
+{
+	kst_listen_flush(st);
+	kst_common_exit(st);
+}
+
+/*
+ * BIO vector receiving function - does not block, but may sleep because
+ * of scheduling policy.
+ */
+static int kst_data_recv_bio_vec(struct kst_state *st, struct bio_vec *bv,
+		unsigned int offset, unsigned int size)
+{
+	struct msghdr msg;
+	struct kvec iov;
+	void *kaddr;
+	int err;
+
+	kaddr = kmap(bv->bv_page);
+
+	iov.iov_base = kaddr + bv->bv_offset + offset;
+	iov.iov_len = size;
+
+	msg.msg_iov = (struct iovec *)&iov;
+	msg.msg_iovlen = 1;
+	msg.msg_name = NULL;
+	msg.msg_namelen = 0;
+	msg.msg_control = NULL;
+	msg.msg_controllen = 0;
+	msg.msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL;
+
+	err = kernel_recvmsg(st->socket, &msg, &iov, 1, iov.iov_len,
+			msg.msg_flags);
+	kunmap(bv->bv_page);
+
+	return err;
+}
+
+/*
+ * BIO vector sending function - does not block, but may sleep because
+ * of scheduling policy.
+ */
+static int kst_data_send_bio_vec(struct kst_state *st, struct bio_vec *bv,
+		unsigned int offset, unsigned int size)
+{
+	return kernel_sendpage(st->socket, bv->bv_page,
+			bv->bv_offset + offset, size,
+			MSG_DONTWAIT | MSG_NOSIGNAL);
+}
+
+static int kst_data_send_bio_vec_slow(struct kst_state *st, struct bio_vec *bv,
+		unsigned int offset, unsigned int size)
+{
+	struct msghdr msg;
+	struct kvec iov;
+	void *addr;
+	int err;
+
+	addr = kmap(bv->bv_page);
+	iov.iov_base = addr + bv->bv_offset + offset;
+	iov.iov_len = size;
+
+	msg.msg_iov = (struct iovec *)&iov;
+	msg.msg_iovlen = 1;
+	msg.msg_name = NULL;
+	msg.msg_namelen = 0;
+	msg.msg_control = NULL;
+	msg.msg_controllen = 0;
+	msg.msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL;
+
+	err = kernel_sendmsg(st->socket, &msg, &iov, 1, iov.iov_len);
+	kunmap(bv->bv_page);
+
+	return err;
+}
+
+static u32 dst_csum_bvec(struct bio_vec *bv, unsigned int offset, unsigned int size)
+{
+	void *addr;
+	u32 csum;
+
+	addr = kmap_atomic(bv->bv_page, KM_USER0);
+	csum =  dst_csum_data(addr + bv->bv_offset + offset, size);
+	kunmap_atomic(addr, KM_USER0);
+
+	return csum;
+}
+
+typedef int (*kst_data_process_bio_vec_t)(struct kst_state *st,
+		struct bio_vec *bv, unsigned int offset, unsigned int size);
+
+/*
+ * @req: processing request.
+ * Contains BIO and all related to its processing info.
+ *
+ * This function sends or receives requested number of pages from given BIO.
+ *
+ * In case of errors negative value is returned and @size,
+ * @index and @off are set to the:
+ * - number of bytes not yet processed (i.e. the rest of the bytes to be
+ *   processed).
+ * - index of the last bio_vec started to be processed (header sent).
+ * - offset of the first byte to be processed in the bio_vec.
+ *
+ * If there are no errors, zero is returned.
+ * -EAGAIN is not an error and is transformed into zero return value,
+ * called must check if @size is zero, in that case whole BIO is processed
+ * and thus req->bio_endio() can be called, othervise new request must be allocated
+ * to be processed later.
+ */
+static int kst_data_process_bio(struct dst_request *req)
+{
+	int err = -ENOSPC;
+	struct dst_remote_request r;
+	kst_data_process_bio_vec_t func;
+	unsigned int cur_size;
+	int use_csum = test_bit(DST_NODE_USE_CSUM, &req->node->flags);
+
+	if (bio_rw(req->bio) == WRITE) {
+		int i;
+
+		func = kst_data_send_bio_vec;
+		for (i=req->idx; i<req->num; ++i) {
+			struct bio_vec *bv = bio_iovec_idx(req->bio, i);
+
+			if (PageSlab(bv->bv_page)) {
+				func = kst_data_send_bio_vec_slow;
+				break;
+			}
+		}
+		r.cmd = cpu_to_be32(DST_WRITE);
+	} else {
+		r.cmd = cpu_to_be32(DST_READ);
+		func = kst_data_recv_bio_vec;
+	}
+
+	dprintk("%s: start: [%c], state: %p, node: %p, start: %llu, idx: %d, num: %d, "
+			"size: %llu, offset: %u, flags: %x, use_csum: %d.\n",
+			__func__, (bio_rw(req->bio) == WRITE)?'W':'R', req->state, req->node,
+			req->start, req->idx, req->num, req->size, req->offset,
+			req->flags, use_csum);
+
+	while (req->idx < req->num) {
+		struct bio_vec *bv = bio_iovec_idx(req->bio, req->idx);
+
+		cur_size = min_t(u64, bv->bv_len - req->offset, req->size);
+
+		dprintk("%s: page: %p, slab: %d, count: %d, max: %d, off: %u, len: %u, req->offset: %u, "
+				"req->size: %llu, cur_size: %u, flags: %x, "
+				"use_csum: %d, req->csum: %x.\n",
+				__func__, bv->bv_page, PageSlab(bv->bv_page),
+				atomic_read(&bv->bv_page->_count), req->bio->bi_vcnt,
+				bv->bv_offset, bv->bv_len,
+				req->offset, req->size, cur_size,
+				req->flags, use_csum, req->tmp_csum);
+
+		if (cur_size == 0) {
+			printk(KERN_ERR "%s: %d/%d: start: %llu, "
+				"bv_offset: %u, bv_len: %u, "
+				"req_offset: %u, req_size: %llu, "
+				"req: %p, bio: %p, err: %d.\n",
+				__func__, req->idx, req->num, req->start,
+				bv->bv_offset, bv->bv_len,
+				req->offset, req->size,
+				req, req->bio, err);
+			BUG();
+		}
+
+		if (!(req->flags & DST_REQ_HEADER_SENT)) {
+			r.sector = cpu_to_be64(req->start);
+			r.offset = cpu_to_be32(bv->bv_offset + req->offset);
+			r.size = cpu_to_be32(cur_size);
+			r.csum = 0;
+
+			if (use_csum && bio_rw(req->bio) == WRITE &&
+					!req->tmp_offset) {
+				req->tmp_offset = req->offset;
+				r.csum = cpu_to_be32(dst_csum_bvec(bv,
+						req->offset, cur_size));
+			}
+
+			err = dst_data_send_header(req->state->socket, &r);
+			dprintk("%s: %d/%d: sending header: cmd: %u, start: %llu, "
+				"bv_offset: %u, bv_len: %u, "
+				"a offset: %u, offset: %u, "
+				"cur_size: %u, err: %d.\n",
+				__func__, req->idx, req->num, be32_to_cpu(r.cmd),
+				req->start, bv->bv_offset, bv->bv_len,
+				bv->bv_offset + req->offset,
+				req->offset, cur_size, err);
+
+			if (err != sizeof(struct dst_remote_request)) {
+				if (err >= 0)
+					err = -EINVAL;
+				break;
+			}
+
+			req->flags |= DST_REQ_HEADER_SENT;
+		}
+
+		if (use_csum && (bio_rw(req->bio) != WRITE) &&
+				!(req->flags & DST_REQ_CHEKSUM_RECV)) {
+			struct dst_remote_request tmp_req;
+
+			err = dst_data_recv_header(req->state->socket, &tmp_req, 0);
+			dprintk("%s: %d/%d: receiving header: start: %llu, "
+				"bv_offset: %u, bv_len: %u, "
+				"a offset: %u, offset: %u, "
+				"cur_size: %u, err: %d.\n",
+				__func__, req->idx, req->num,
+				req->start, bv->bv_offset, bv->bv_len,
+				bv->bv_offset + req->offset,
+				req->offset, cur_size, err);
+
+			if (err != sizeof(struct dst_remote_request)) {
+				if (err >= 0)
+					err = -EINVAL;
+				break;
+			}
+
+			if (req->tmp_csum) {
+				printk(KERN_ERR "%s: req: %p, old csum: %x, new: %x.\n",
+						__func__, req, req->tmp_csum,
+						be32_to_cpu(tmp_req.csum));
+				BUG_ON(1);
+			}
+
+			dprintk("%s: req: %p, old csum: %x, new: %x.\n",
+					__func__, req, req->tmp_csum,
+					be32_to_cpu(tmp_req.csum));
+			req->tmp_csum = be32_to_cpu(tmp_req.csum);
+
+			req->flags |= DST_REQ_CHEKSUM_RECV;
+		}
+
+		err = func(req->state, bv, req->offset, cur_size);
+		if (err <= 0)
+			break;
+
+		req->offset += err;
+		req->size -= err;
+
+		if (req->offset != bv->bv_len) {
+			dprintk("%s: %d/%d: this: start: %llu, bv_offset: %u, "
+				"bv_len: %u, offset: %u, "
+				"cur_size: %u, err: %d.\n",
+				__func__, req->idx, req->num, req->start,
+				bv->bv_offset, bv->bv_len,
+				req->offset, cur_size, err);
+			err = -EAGAIN;
+			break;
+		}
+
+		if (use_csum && bio_rw(req->bio) != WRITE) {
+			u32 csum = dst_csum_bvec(bv, req->tmp_offset,
+					bv->bv_len - req->tmp_offset);
+
+			dprintk("%s: req: %p, csum: %x, received csum: %x.\n",
+					__func__, req, csum, req->tmp_csum);
+
+			if (csum != req->tmp_csum) {
+				if (printk_ratelimit()) {
+					printk(KERN_INFO "%s: %d/%d: broken checksum: start: %llu, "
+						"bv_offset: %u, bv_len: %u, "
+						"a offset: %u, offset: %u, "
+						"cur_size: %u, orig_size: %llu.\n",
+						__func__, req->idx, req->num,
+						req->start, bv->bv_offset, bv->bv_len,
+						bv->bv_offset + req->offset,
+						req->offset, cur_size, req->orig_size);
+					printk(KERN_INFO "%s: broken checksum: req: %p, csum: %x, "
+						"should be: %x, flags: %x, "
+						"req->tmp_offset: %u, rw: %lu.\n",
+						__func__, req, csum, req->tmp_csum,
+						req->flags, req->tmp_offset, bio_rw(req->bio));
+				}
+
+				req->offset -= err;
+				req->size += err;
+
+				err = -EREMOTEIO;
+				break;
+			}
+		}
+
+		req->offset = 0;
+		req->idx++;
+		req->flags &= ~(DST_REQ_HEADER_SENT | DST_REQ_CHEKSUM_RECV);
+		req->tmp_csum = 0;
+		req->start += to_sector(bv->bv_len);
+	}
+
+	if (err <= 0 && err != -EAGAIN) {
+		if (err == 0)
+			err = -ECONNRESET;
+	} else
+		err = 0;
+
+	if (err < 0 || (req->idx == req->num && req->size)) {
+		dprintk("%s: return: idx: %d, num: %d, offset: %u, "
+				"size: %llu, err: %d.\n",
+			__func__, req->idx, req->num, req->offset,
+			req->size, err);
+	}
+	dprintk("%s: end: start: %llu, idx: %d, num: %d, "
+			"size: %llu, offset: %u.\n",
+		__func__, req->start, req->idx, req->num,
+		req->size, req->offset);
+
+	return err;
+}
+
+void kst_bio_endio(struct dst_request *req, int err)
+{
+	if (err && printk_ratelimit())
+		printk(KERN_INFO "%s: freeing bio: %p, bi_size: %u, "
+			"orig_size: %llu, req: %p, err: %d.\n",
+		__func__, req->bio, req->bio->bi_size, req->orig_size,
+		req, err);
+	bio_endio(req->bio, req->orig_size, err);
+}
+EXPORT_SYMBOL_GPL(kst_bio_endio);
+
+/*
+ * This callback is invoked by worker thread to process given request.
+ */
+int kst_data_callback(struct dst_request *req, unsigned int revents)
+{
+	int err;
+
+	dprintk("%s: req: %p, num: %d, idx: %d, bio: %p, "
+			"revents: %x, flags: %x.\n",
+			__func__, req, req->num, req->idx, req->bio,
+			revents, req->flags);
+
+	if (req->flags & DST_REQ_EXPORT_READ)
+		return 1;
+
+	err = kst_data_process_bio(req);
+
+	if (revents & (POLLERR | POLLHUP | POLLRDHUP))
+		err = -EPIPE;
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(kst_data_callback);
+
+struct dst_request *dst_clone_request(struct dst_request *req, mempool_t *pool)
+{
+	struct dst_request *new_req;
+
+	new_req = mempool_alloc(pool, GFP_NOIO);
+	if (!new_req)
+		return NULL;
+
+	memset(new_req, 0, sizeof(struct dst_request));
+
+	dprintk("%s: req: %p, new_req: %p.\n", __func__, req, new_req);
+
+	if (req) {
+		new_req->bio = req->bio;
+		new_req->state = req->state;
+		new_req->node = req->node;
+		new_req->idx = req->idx;
+		new_req->num = req->num;
+		new_req->size = req->size;
+		new_req->orig_size = req->orig_size;
+		new_req->offset = req->offset;
+		new_req->tmp_offset = req->tmp_offset;
+		new_req->tmp_csum = req->tmp_csum;
+		new_req->start = req->start;
+		new_req->flags = req->flags;
+		new_req->bio_endio = req->bio_endio;
+		new_req->priv = req->priv;
+	}
+
+	return new_req;
+}
+EXPORT_SYMBOL_GPL(dst_clone_request);
+
+void dst_free_request(struct dst_request *req)
+{
+	dprintk("%s: free req: %p, pool: %p, bio: %p, state: %p, node: %p.\n",
+			__func__, req, req->node->w->req_pool,
+			req->bio, req->state, req->node);
+	mempool_free(req, req->node->w->req_pool);
+}
+EXPORT_SYMBOL_GPL(dst_free_request);
+
+/*
+ * This is main data processing function, eventually invoked from block layer.
+ * It tries to complte request, but if it is about to block, it allocates
+ * new request and queues it to main worker to be processed when events allow.
+ */
+static int kst_data_push(struct dst_request *req)
+{
+	struct kst_state *st = req->state;
+	struct dst_request *new_req;
+	unsigned int revents;
+	int err, locked = 0;
+
+	dprintk("%s: start: %llu, size: %llu, bio: %p.\n",
+			__func__, req->start, req->size, req->bio);
+
+	if (!list_empty(&st->request_list) || (req->flags & DST_REQ_ALWAYS_QUEUE))
+		goto alloc_new_req;
+
+	if (mutex_trylock(&st->request_lock)) {
+		locked = 1;
+
+		if (!list_empty(&st->request_list))
+			goto alloc_new_req;
+
+		revents = st->socket->ops->poll(NULL, st->socket, NULL);
+		if (revents & POLLOUT) {
+			err = kst_data_process_bio(req);
+			if (err < 0)
+				goto out_unlock;
+
+			if (!req->size)
+				goto out_bio_endio;
+		}
+	}
+
+alloc_new_req:
+	err = -ENOMEM;
+	new_req = dst_clone_request(req, req->node->w->req_pool);
+	if (!new_req)
+		goto out_unlock;
+
+	new_req->callback = &kst_data_callback;
+
+	if (!locked)
+		mutex_lock(&st->request_lock);
+
+	locked = 1;
+
+	err = kst_enqueue_req(st, new_req);
+	if (err)
+		goto out_unlock;
+	mutex_unlock(&st->request_lock);
+
+	err = 0;
+	goto out;
+
+out_bio_endio:
+	req->bio_endio(req, err);
+out_unlock:
+	if (locked)
+		mutex_unlock(&st->request_lock);
+	locked = 0;
+
+	if (err) {
+		err = kst_error(st, err);
+		if (!err)
+			goto alloc_new_req;
+	}
+
+	if (err && printk_ratelimit()) {
+		printk(KERN_INFO "%s: error [%c], start: %llu, idx: %d, num: %d, "
+				"size: %llu, offset: %u, err: %d.\n",
+			__func__, (bio_rw(req->bio) == WRITE)?'W':'R',
+			req->start, req->idx, req->num, req->size,
+			req->offset, err);
+	}
+
+out:
+
+	kst_wake(st);
+	return err;
+}
+
+/*
+ * Remote node initialization callback.
+ */
+static int kst_data_init(struct kst_state *st, void *data)
+{
+	int err;
+
+	st->socket = data;
+	st->socket->sk->sk_allocation = GFP_NOIO;
+	/*
+	 * Why not?
+	 */
+	st->socket->sk->sk_sndbuf = st->socket->sk->sk_sndbuf = 1024*1024*10;
+
+	err = kst_poll_init(st);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+/*
+ * Remote node recovery function - tries to reconnect to given target.
+ */
+static int kst_data_recovery(struct kst_state *st, int err)
+{
+	struct socket *sock;
+	struct sockaddr addr;
+	int addrlen;
+	struct dst_request *req;
+
+	if (err != -ECONNRESET && err != -EPIPE) {
+		dprintk("%s: state %p does not know how "
+				"to recover from error %d.\n",
+				__func__, st, err);
+		return err;
+	}
+
+	err = sock_create(st->socket->ops->family, st->socket->type,
+			st->socket->sk->sk_protocol, &sock);
+	if (err < 0)
+		goto err_out_exit;
+
+	sock->sk->sk_sndtimeo = sock->sk->sk_rcvtimeo =
+		msecs_to_jiffies(DST_DEFAULT_TIMEO);
+
+	err = sock->ops->getname(st->socket, &addr, &addrlen, 2);
+	if (err)
+		goto err_out_destroy;
+
+	err = sock->ops->connect(sock, &addr, addrlen, 0);
+	if (err)
+		goto err_out_destroy;
+
+	kst_poll_exit(st);
+	kst_sock_release(st);
+
+	mutex_lock(&st->request_lock);
+	err = st->ops->init(st, sock);
+	if (!err) {
+		/*
+		 * After reconnection is completed all requests
+		 * must be resent from the state they were finished previously,
+		 * but with new headers.
+		 */
+		list_for_each_entry(req, &st->request_list, request_list_entry)
+			req->flags &= ~(DST_REQ_HEADER_SENT | DST_REQ_CHEKSUM_RECV);
+	}
+	mutex_unlock(&st->request_lock);
+	if (err < 0)
+		goto err_out_destroy;
+
+	kst_wake(st);
+	dprintk("%s: reconnected.\n", __func__);
+
+	return 0;
+
+err_out_destroy:
+	sock_release(sock);
+err_out_exit:
+	dprintk("%s: recovery failed: st: %p, err: %d.\n", __func__, st, err);
+	return err;
+}
+
+/*
+ * Local exporting node end IO callbacks.
+ */
+static int kst_export_write_end_io(struct bio *bio, unsigned int size, int err)
+{
+	dprintk("%s: bio: %p, size: %u, idx: %d, num: %d, err: %d.\n",
+		__func__, bio, bio->bi_size, bio->bi_idx, bio->bi_vcnt, err);
+
+	if (bio->bi_size)
+		return 1;
+
+	kst_export_put_bio(bio);
+	return 0;
+}
+
+static int kst_export_read_end_io(struct bio *bio, unsigned int size, int err)
+{
+	struct dst_request *req = bio->bi_private;
+	struct kst_state *st = req->state;
+	int use_csum = test_bit(DST_NODE_USE_CSUM, &req->node->flags);
+
+	dprintk("%s: bio: %p, req: %p, size: %u, idx: %d, num: %d, err: %d.\n",
+		__func__, bio, req, bio->bi_size, bio->bi_idx,
+		bio->bi_vcnt, err);
+
+	if (bio->bi_size)
+		return 1;
+
+	if (err) {
+		kst_export_put_bio(bio);
+		return 0;
+	}
+
+	bio->bi_size = req->size = req->orig_size;
+	bio->bi_rw = WRITE;
+	bio->bi_end_io = kst_export_write_end_io;
+	if (use_csum)
+		req->flags &= ~(DST_REQ_HEADER_SENT | DST_REQ_CHEKSUM_RECV);
+
+	/*
+	 * This is a race with kst_data_callback(), which checks
+	 * this bit to determine if it can or can not process given
+	 * request. This does not harm actually, since subsequent
+	 * state wakeup will call it again and thus will pick
+	 * given request in time.
+	 */
+	req->flags &= ~DST_REQ_EXPORT_READ;
+	kst_wake(st);
+	return 0;
+}
+
+/*
+ * This callback is invoked each time new request from remote
+ * node to given local export node is received.
+ * It allocates new block IO request and queues it for processing.
+ */
+static int kst_export_ready(struct kst_state *st)
+{
+	struct dst_remote_request r;
+	struct bio *bio;
+	int err, nr, i;
+	struct dst_request *req;
+	unsigned int revents = st->socket->ops->poll(NULL, st->socket, NULL);
+
+	if (revents & (POLLERR | POLLHUP)) {
+		err = -EPIPE;
+		goto err_out_exit;
+	}
+
+	if (!(revents & POLLIN) || !list_empty(&st->request_list))
+		return 0;
+
+	err = dst_data_recv_header(st->socket, &r, 1);
+	if (err != sizeof(struct dst_remote_request)) {
+		err = -ECONNRESET;
+		goto err_out_exit;
+	}
+
+	kst_convert_header(&r);
+
+	dprintk("\n%s: st: %p, cmd: %u, sector: %llu, size: %u, "
+			"csum: %x, offset: %u.\n",
+			__func__, st, r.cmd, r.sector,
+			r.size, r.csum, r.offset);
+
+	err = -EINVAL;
+	if (r.cmd != DST_READ && r.cmd != DST_WRITE && r.cmd != DST_REMOTE_CFG)
+		goto err_out_exit;
+
+	if ((s64)(r.sector + to_sector(r.size)) < 0 ||
+		(r.sector + to_sector(r.size)) > st->node->size ||
+		r.offset >= PAGE_SIZE)
+		goto err_out_exit;
+
+	if (r.cmd == DST_REMOTE_CFG) {
+		r.sector = st->node->size;
+
+		if (test_bit(DST_NODE_USE_CSUM, &st->node->flags))
+			r.csum = 1;
+
+		kst_convert_header(&r);
+
+		err = dst_data_send_header(st->socket, &r);
+		if (err != sizeof(struct dst_remote_request)) {
+			err = -EINVAL;
+			goto err_out_exit;
+		}
+		kst_wake(st);
+		return 0;
+	}
+
+	nr = DIV_ROUND_UP(r.size, PAGE_SIZE);
+
+	while (r.size) {
+		int nr_pages = min(BIO_MAX_PAGES, nr);
+		unsigned int size;
+		struct page *page;
+
+		err = -ENOMEM;
+		req = dst_clone_request(NULL, st->node->w->req_pool);
+		if (!req)
+			goto err_out_exit;
+
+		bio = bio_alloc(GFP_NOIO, nr_pages);
+		if (!bio)
+			goto err_out_free_req;
+
+		req->flags = DST_REQ_EXPORT | DST_REQ_HEADER_SENT |
+				DST_REQ_CHEKSUM_RECV;
+		req->bio = bio;
+		req->state = st;
+		req->node = st->node;
+		req->callback = &kst_data_callback;
+		req->bio_endio = &kst_bio_endio;
+
+		req->tmp_offset = 0;
+		req->tmp_csum = r.csum;
+
+		/*
+		 * Yes, looks a bit weird.
+		 * Logic is simple - for local exporting node all operations
+		 * are reversed compared to usual nodes, since usual nodes
+		 * process remote data and local export node process remote
+		 * requests, so that writing data means sending data to
+		 * remote node and receiving on the local export one.
+		 *
+		 * So, to process writing to the exported node we need first
+		 * to receive data from the net (i.e. to perform READ
+		 * operationin terms of usual node), and then put it to the
+		 * storage (WRITE command, so it will be changed before
+		 * calling generic_make_request()).
+		 *
+		 * To process read request from the exported node we need
+		 * first to read it from storage (READ command for BIO)
+		 * and then send it over the net (perform WRITE operation
+		 * in terms of network).
+		 */
+		if (r.cmd == DST_WRITE) {
+			req->flags |= DST_REQ_EXPORT_WRITE;
+			bio->bi_end_io = kst_export_write_end_io;
+		} else {
+			req->flags |= DST_REQ_EXPORT_READ;
+			bio->bi_end_io = kst_export_read_end_io;
+		}
+		bio->bi_rw = READ;
+		bio->bi_private = req;
+		bio->bi_sector = r.sector;
+		bio->bi_bdev = st->node->bdev;
+
+		for (i = 0; i < nr_pages; ++i) {
+			page = alloc_page(GFP_NOIO);
+			if (!page)
+				break;
+
+			size = min_t(u32, PAGE_SIZE - r.offset, r.size);
+
+			err = bio_add_page(bio, page, size, 0);
+			dprintk("%s: %d/%d: page: %p, size: %u, "
+					"offset: %u (used zero), err: %d.\n",
+					__func__, i, nr_pages, page, size,
+					r.offset, err);
+			if (err <= 0)
+				break;
+
+			if (err == size)
+				nr--;
+
+			r.size -= err;
+			r.sector += to_sector(err);
+
+			if (!r.size)
+				break;
+		}
+
+		if (!bio->bi_vcnt) {
+			err = -ENOMEM;
+			goto err_out_put;
+		}
+
+		req->size = req->orig_size = bio->bi_size;
+		req->start = bio->bi_sector;
+		req->idx = 0;
+		req->num = bio->bi_vcnt;
+
+		dprintk("%s: submitting: bio: %p, req: %p, start: %llu, "
+			"size: %llu, idx: %d, num: %d, offset: %u, csum: %x.\n",
+			__func__, bio, req, req->start, req->size,
+			req->idx, req->num, req->offset, req->tmp_csum);
+
+		err = kst_enqueue_req(st, req);
+		if (err)
+			goto err_out_put;
+
+		if (r.cmd == DST_READ) {
+			generic_make_request(bio);
+		}
+	}
+
+	kst_wake(st);
+	return 0;
+
+err_out_put:
+	bio_put(bio);
+err_out_free_req:
+	dst_free_request(req);
+err_out_exit:
+	return err;
+}
+
+static void kst_export_exit(struct kst_state *st)
+{
+	struct dst_node *n = st->node;
+
+	kst_common_exit(st);
+	dst_node_put(n);
+}
+
+static struct kst_state_ops kst_data_export_ops = {
+	.init = &kst_data_init,
+	.push = &kst_data_push,
+	.exit = &kst_export_exit,
+	.ready = &kst_export_ready,
+};
+
+/*
+ * This callback is invoked each time listening socket for
+ * given local export node becomes ready.
+ * It creates new state for connected client and queues for processing.
+ */
+static int kst_listen_ready(struct kst_state *st)
+{
+	struct socket *newsock;
+	struct saddr addr;
+	struct kst_state *newst;
+	int err;
+	unsigned int revents, permissions = 0;
+	struct dst_secure *s;
+
+	revents = st->socket->ops->poll(NULL, st->socket, NULL);
+	if (!(revents & POLLIN))
+		return 1;
+
+	err = sock_create(st->socket->ops->family, st->socket->type,
+			st->socket->sk->sk_protocol, &newsock);
+	if (err)
+		goto err_out_exit;
+
+	err = st->socket->ops->accept(st->socket, newsock, 0);
+	if (err)
+		goto err_out_put;
+
+	if (newsock->ops->getname(newsock, (struct sockaddr *)&addr,
+				  (int *)&addr.sa_data_len, 2) < 0) {
+		err = -ECONNABORTED;
+		goto err_out_put;
+	}
+
+	list_for_each_entry(s, &st->request_list, sec_entry) {
+		void *sec_addr, *new_addr;
+
+		sec_addr = ((void *)&s->sec.addr) + s->sec.check_offset;
+		new_addr = ((void *)&addr) + s->sec.check_offset;
+
+		if (!memcmp(sec_addr, new_addr,
+				addr.sa_data_len - s->sec.check_offset)) {
+			permissions = s->sec.permissions;
+			break;
+		}
+	}
+
+	/*
+	 * So far only reading and writing are supported.
+	 * Block device does not know about anything else,
+	 * but as far as I recall, there was a prognosis,
+	 * that computer will never require more than 640kb of RAM.
+	 */
+	if (permissions == 0) {
+		err = -EPERM;
+		goto err_out_put;
+	}
+
+	if (st->socket->ops->family == AF_INET) {
+		struct sockaddr_in *sin = (struct sockaddr_in *)&addr;
+		printk(KERN_INFO "%s: Client: %u.%u.%u.%u:%d.\n", __func__,
+			NIPQUAD(sin->sin_addr.s_addr), ntohs(sin->sin_port));
+	} else if (st->socket->ops->family == AF_INET6) {
+		struct sockaddr_in6 *sin = (struct sockaddr_in6 *)&addr;
+		printk(KERN_INFO "%s: Client: "
+			"%04x:%04x:%04x:%04x:%04x:%04x:%04x:%04x:%d",
+			__func__,
+			NIP6(sin->sin6_addr), ntohs(sin->sin6_port));
+	}
+
+	dst_node_get(st->node);
+	newst = kst_state_init(st->node, permissions,
+			&kst_data_export_ops, newsock);
+	if (IS_ERR(newst)) {
+		err = PTR_ERR(newst);
+		goto err_out_put;
+	}
+
+	/*
+	 * Negative return value means error, positive - stop this state
+	 * processing. Zero allows to check state for pending requests.
+	 * Listening socket contains security objects in request list,
+	 * since it does not have any requests.
+	 */
+	return 1;
+
+err_out_put:
+	sock_release(newsock);
+err_out_exit:
+	return 1;
+}
+
+static int kst_listen_init(struct kst_state *st, void *data)
+{
+	int err = -ENOMEM, i;
+	struct dst_le_template *tmp = data;
+	struct dst_secure *s;
+
+	for (i=0; i<tmp->le->secure_attr_num; ++i) {
+		s = kmalloc(sizeof(struct dst_secure), GFP_KERNEL);
+		if (!s)
+			goto err_out_exit;
+
+		memcpy(&s->sec, tmp->data, sizeof(struct dst_secure_user));
+
+		list_add_tail(&s->sec_entry, &st->request_list);
+		tmp->data += sizeof(struct dst_secure_user);
+
+		if (s->sec.addr.sa_family == AF_INET) {
+			struct sockaddr_in *sin =
+				(struct sockaddr_in *)&s->sec.addr;
+			printk(KERN_INFO "%s: Client: %u.%u.%u.%u:%d, "
+					"permissions: %x.\n",
+				__func__, NIPQUAD(sin->sin_addr.s_addr),
+				ntohs(sin->sin_port), s->sec.permissions);
+		} else if (s->sec.addr.sa_family == AF_INET6) {
+			struct sockaddr_in6 *sin =
+				(struct sockaddr_in6 *)&s->sec.addr;
+			printk(KERN_INFO "%s: Client: "
+				"%04x:%04x:%04x:%04x:%04x:%04x:%04x:%04x:%d, "
+				"permissions: %x.\n",
+				__func__, NIP6(sin->sin6_addr),
+				ntohs(sin->sin6_port), s->sec.permissions);
+		}
+	}
+
+	err = kst_sock_create(st, &tmp->le->rctl.addr, tmp->le->rctl.type,
+			tmp->le->rctl.proto, tmp->le->backlog);
+	if (err)
+		goto err_out_exit;
+
+	err = kst_poll_init(st);
+	if (err)
+		goto err_out_release;
+
+	return 0;
+
+err_out_release:
+	kst_sock_release(st);
+err_out_exit:
+	kst_listen_flush(st);
+	return err;
+}
+
+/*
+ * Operations for different types of states.
+ * There are three:
+ * data state - created for remote node, when distributed storage connects
+ * 	to remote node, which contain data.
+ * listen state - created for local export node, when remote distributed
+ * 	storage's node connects to given node to get/put data.
+ * data export state - created for each client connected to above listen
+ * 	state.
+ */
+static struct kst_state_ops kst_listen_ops = {
+	.init = &kst_listen_init,
+	.exit = &kst_listen_exit,
+	.ready = &kst_listen_ready,
+};
+static struct kst_state_ops kst_data_ops = {
+	.init = &kst_data_init,
+	.push = &kst_data_push,
+	.exit = &kst_common_exit,
+	.recovery = &kst_data_recovery,
+};
+
+struct kst_state *kst_listener_state_init(struct dst_node *node,
+		struct dst_le_template *tmp)
+{
+	return kst_state_init(node, DST_PERM_READ | DST_PERM_WRITE,
+			&kst_listen_ops, tmp);
+}
+
+struct kst_state *kst_data_state_init(struct dst_node *node,
+		struct socket *newsock)
+{
+	return kst_state_init(node, DST_PERM_READ | DST_PERM_WRITE,
+			&kst_data_ops, newsock);
+}
+
+/*
+ * Remove all workers and associated states.
+ */
+void kst_exit_all(void)
+{
+	struct kst_worker *w, *n;
+
+	list_for_each_entry_safe(w, n, &kst_worker_list, entry) {
+		kst_worker_exit(w);
+	}
+}

[4/4] DST: Algorithms used in distributed storage.

[Evgeniy Polyakov]

Algorithms used in distributed storage.
Mirror and linear mapping code.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


diff --git a/drivers/block/dst/alg_linear.c b/drivers/block/dst/alg_linear.c
new file mode 100644
index 0000000..836764d
--- /dev/null
+++ b/drivers/block/dst/alg_linear.c
@@ -0,0 +1,114 @@
+/*
+ * 2007+ Copyright (c) Evgeniy Polyakov <johnpol@2ka.mipt.ru>
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/dst.h>
+
+static struct dst_alg *alg_linear;
+
+/*
+ * This callback is invoked when node is removed from storage.
+ */
+static void dst_linear_del_node(struct dst_node *n)
+{
+}
+
+/*
+ * This callback is invoked when node is added to storage.
+ */
+static int dst_linear_add_node(struct dst_node *n)
+{
+	struct dst_storage *st = n->st;
+	struct block_device *bdev;
+
+	dprintk("%s: disk_size: %llu, node_size: %llu.\n",
+			__func__, st->disk_size, n->size);
+
+	mutex_lock(&st->tree_lock);
+	n->start = st->disk_size;
+	st->disk_size += n->size;
+	set_capacity(st->disk, st->disk_size);
+	
+	bdev = bdget_disk(st->disk, 0);
+	if (bdev) {
+		mutex_lock(&bdev->bd_inode->i_mutex);
+		i_size_write(bdev->bd_inode, to_bytes(st->disk_size));
+		mutex_unlock(&bdev->bd_inode->i_mutex);
+		bdput(bdev);
+	}
+	mutex_unlock(&st->tree_lock);
+
+	return 0;
+}
+
+static int dst_linear_remap(struct dst_request *req)
+{
+	int err;
+
+	if (req->node->bdev) {
+		generic_make_request(req->bio);
+		return 0;
+	}
+
+	err = kst_check_permissions(req->state, req->bio);
+	if (err)
+		return err;
+
+	return req->state->ops->push(req);
+}
+
+/*
+ * Failover callback - it is invoked each time error happens during
+ * request processing.
+ */
+static int dst_linear_error(struct kst_state *st, int err)
+{
+	if (err)
+		set_bit(DST_NODE_FROZEN, &st->node->flags);
+	else
+		clear_bit(DST_NODE_FROZEN, &st->node->flags);
+	return 0;
+}
+
+static struct dst_alg_ops alg_linear_ops = {
+	.remap		= dst_linear_remap,
+	.add_node 	= dst_linear_add_node,
+	.del_node 	= dst_linear_del_node,
+	.error		= dst_linear_error,
+	.owner		= THIS_MODULE,
+};
+
+static int __devinit alg_linear_init(void)
+{
+	alg_linear = dst_alloc_alg("alg_linear", &alg_linear_ops);
+	if (!alg_linear)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void __devexit alg_linear_exit(void)
+{
+	dst_remove_alg(alg_linear);
+}
+
+module_init(alg_linear_init);
+module_exit(alg_linear_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Evgeniy Polyakov <johnpol@2ka.mipt.ru>");
+MODULE_DESCRIPTION("Linear distributed algorithm.");
diff --git a/drivers/block/dst/alg_mirror.c b/drivers/block/dst/alg_mirror.c
new file mode 100644
index 0000000..c10d582
--- /dev/null
+++ b/drivers/block/dst/alg_mirror.c
@@ -0,0 +1,1536 @@
+/*
+ * 2007+ Copyright (c) Evgeniy Polyakov <johnpol@2ka.mipt.ru>
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/poll.h>
+#include <linux/dst.h>
+#include <linux/vmstat.h>
+
+struct dst_write_entry
+{
+	int		error;
+	u32		size;
+	u64		start;
+};
+#define DST_LOG_ENTRIES_PER_PAGE	(PAGE_SIZE/sizeof(struct dst_write_entry))
+
+struct dst_mirror_node_data
+{
+	u64			age;
+	u64			num, write_idx, resync_idx;
+};
+
+struct dst_mirror_log
+{
+	unsigned int		nr_pages;
+	struct dst_write_entry	**entries;
+};
+
+struct dst_mirror_priv
+{
+	u64			resync_start, resync_size;
+	atomic_t		resync_num;
+	struct completion	resync_complete;
+	struct delayed_work	resync_work;
+	unsigned int		resync_timeout;
+
+	u64			last_start;
+	
+	spinlock_t		resync_wait_lock;
+	struct list_head	resync_wait_list;
+	int			resync_wait_num;
+	int			full_resync;
+
+	spinlock_t		backlog_lock;
+	struct list_head	backlog_list;
+
+	struct dst_node		*node;
+
+	u64			old_age, ndp_sector;
+	struct dst_mirror_node_data	data;
+
+	spinlock_t		log_lock;
+	struct dst_mirror_log	log;
+};
+
+struct dst_mirror_sync_container
+{
+	struct list_head	sync_entry;
+	u64			start, size;
+	struct dst_node		*node;
+	struct bio		*bio;
+};
+
+static struct dst_alg *alg_mirror;
+static struct bio_set *dst_mirror_bio_set;
+
+static int dst_mirror_resync(struct dst_node *n, int ndp);
+
+static int dst_mirror_mark_notsync(struct dst_node *n)
+{
+	if (!test_and_set_bit(DST_NODE_NOTSYNC, &n->flags)) {
+		struct dst_mirror_priv *priv = n->priv;
+		printk(KERN_NOTICE "%s: not synced node n: %p.\n", __func__, n);
+
+		priv->data.resync_idx = priv->data.write_idx;
+		return 1;
+	}
+
+	return 0;
+}
+
+static void dst_mirror_mark_node_sync(struct dst_node *n)
+{
+	struct dst_mirror_priv *priv = n->priv;
+
+	if (test_and_clear_bit(DST_NODE_NOTSYNC, &n->flags))
+		printk(KERN_NOTICE "%s: node: %p, %llu:%llu synchronization "
+				"has been completed.\n",
+			__func__, n, n->start, n->size);
+
+	priv->full_resync = 0;
+	complete(&priv->resync_complete);
+}
+
+static ssize_t dst_mirror_mark_dirty(struct device *dev, struct device_attribute *attr,
+			 const char *buf, size_t count)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+
+	dst_mirror_mark_notsync(n);
+	return count;
+}
+
+static ssize_t dst_mirror_mark_clean(struct device *dev, struct device_attribute *attr,
+			 const char *buf, size_t count)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+
+	dst_mirror_mark_node_sync(n);
+	return count;
+}
+
+static ssize_t dst_mirror_show_state(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+
+	return sprintf(buf, "%s\n", test_bit(DST_NODE_NOTSYNC, &n->flags) ? "notsync" : "sync");
+}
+
+static ssize_t dst_mirror_show_resync_timeout(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+	struct dst_mirror_priv *priv = n->priv;
+
+	return sprintf(buf, "%u\n", priv->resync_timeout);
+}
+
+static ssize_t dst_mirror_show_resync_size(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+	struct dst_mirror_priv *priv = n->priv;
+
+	return sprintf(buf, "%llu\n", priv->resync_size);
+}
+
+static ssize_t dst_mirror_set_resync_size(struct device *dev, struct device_attribute *attr,
+			 const char *buf, size_t count)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+	struct dst_mirror_priv *priv = n->priv;
+	unsigned long size;
+
+	size = simple_strtoul(buf, NULL, 0);
+
+	if (size > n->st->disk_size)
+		return -E2BIG;
+
+	priv->resync_size = size;
+
+	return count;
+}
+
+static ssize_t dst_mirror_show_log_num(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+	struct dst_mirror_priv *priv = n->priv;
+
+	return sprintf(buf, "%llu\n", priv->data.num);
+}
+
+static ssize_t dst_mirror_set_resync_timeout(struct device *dev, struct device_attribute *attr,
+			 const char *buf, size_t count)
+{
+	struct dst_node *n = container_of(dev, struct dst_node, device);
+	struct dst_mirror_priv *priv = n->priv;
+	unsigned long tm;
+
+	tm = simple_strtoul(buf, NULL, 0);
+
+	if (tm < 100 || tm > 30000)
+		return -EINVAL;
+
+	priv->resync_timeout = (unsigned int)tm;
+
+	return count;
+}
+
+static struct device_attribute dst_mirror_attrs[] = {
+	__ATTR(dirty, S_IWUSR, NULL, dst_mirror_mark_dirty),
+	__ATTR(clean, S_IWUSR, NULL, dst_mirror_mark_clean),
+	__ATTR(resync_size, S_IWUSR | S_IRUGO, dst_mirror_show_resync_size,
+			dst_mirror_set_resync_size),
+	__ATTR(resync_timeout, S_IWUSR | S_IRUGO, dst_mirror_show_resync_timeout,
+			dst_mirror_set_resync_timeout),
+	__ATTR(state, S_IRUSR, dst_mirror_show_state, NULL),
+	__ATTR(log_num, S_IRUSR, dst_mirror_show_log_num, NULL),
+};
+
+static void dst_mirror_handle_priv(struct dst_node *n)
+{
+	if (n->priv) {
+		int err, i;
+
+		for (i=0; i<ARRAY_SIZE(dst_mirror_attrs); ++i)
+			err = device_create_file(&n->device,
+					&dst_mirror_attrs[i]);
+	}
+}
+
+static void dst_mirror_destructor(struct bio *bio)
+{
+	dprintk("%s: bio: %p.\n", __func__, bio);
+	bio_free(bio, dst_mirror_bio_set);
+}
+
+struct dst_mirror_ndp
+{
+	int			err;
+	struct page		*page;
+	struct completion	complete;
+};
+
+static void dst_mirror_ndb_complete(struct dst_mirror_ndp *cmp, int err)
+{
+	cmp->err = err;
+	dprintk("%s: completing request: cmp: %p, err: %d.\n",
+			__func__, cmp, err);
+	complete(&cmp->complete);
+}
+
+static void dst_mirror_ndp_bio_endio(struct dst_request *req, int err)
+{
+	struct dst_mirror_ndp *cmp = req->bio->bi_private;
+
+	dst_mirror_ndb_complete(cmp, err);
+}
+
+static int dst_mirror_ndp_end_io(struct bio *bio, unsigned int size, int err)
+{
+	struct dst_mirror_ndp *cmp = bio->bi_private;
+
+	if (bio->bi_size)
+		return 0;
+
+	dst_mirror_ndb_complete(cmp, err);
+	return 0;
+}
+
+/*
+ * This function reads or writes node's private data from underlying media.
+ */
+static int dst_mirror_process_node_data(struct dst_node *n,
+		struct dst_mirror_node_data *ndata, int op)
+{
+	struct bio *bio;
+	int err = -ENOMEM;
+	struct dst_mirror_ndp *cmp;
+	struct dst_mirror_priv *priv = n->priv;
+	void *addr;
+
+	cmp = kzalloc(sizeof(struct dst_mirror_ndp), GFP_KERNEL);
+	if (!cmp)
+		goto err_out_exit;
+
+	cmp->page = alloc_page(GFP_NOIO);
+	if (!cmp->page)
+		goto err_out_free_cmp;
+
+	addr = kmap(cmp->page);
+
+	init_completion(&cmp->complete);
+
+	if (op == WRITE)
+		memcpy(addr, ndata, sizeof(struct dst_mirror_node_data));
+
+	bio = bio_alloc_bioset(GFP_NOIO, 1, dst_mirror_bio_set);
+	if (!bio)
+		goto err_out_free_page;
+
+	bio->bi_rw = op;
+	bio->bi_private = cmp;
+	bio->bi_sector = priv->ndp_sector;
+	bio->bi_bdev = n->bdev;
+	bio->bi_destructor = dst_mirror_destructor;
+	bio->bi_end_io = dst_mirror_ndp_end_io;
+
+	err = bio_add_pc_page(n->st->queue, bio, cmp->page, 512, 0);
+	if (err <= 0)
+		goto err_out_free_bio;
+
+	if (n->bdev) {
+		generic_make_request(bio);
+	} else {
+		struct dst_request req;
+
+		memset(&req, 0, sizeof(struct dst_request));
+		dst_fill_request(&req, bio, bio->bi_sector, n,
+				&dst_mirror_ndp_bio_endio);
+
+		err = req.state->ops->push(&req);
+		if (err)
+			req.bio_endio(&req, err);
+	}
+
+	dprintk("%s: waiting for completion: bio: %p, cmp: %p.\n",
+			__func__, bio, cmp);
+
+	wait_for_completion(&cmp->complete);
+
+	err = cmp->err;
+	if (!err && (op != WRITE))
+		memcpy(ndata, addr, sizeof(struct dst_mirror_node_data));
+
+	kunmap(cmp->page);
+
+	dprintk("%s: freeing bio: %p, err: %d.\n", __func__, bio, err);
+
+err_out_free_bio:
+	bio_put(bio);
+err_out_free_page:
+	kunmap(cmp->page);
+	__free_page(cmp->page);
+err_out_free_cmp:
+	kfree(cmp);
+err_out_exit:
+	return err;
+}
+
+/*
+ * This function reads node's private data from underlying media.
+ */
+static int dst_mirror_read_node_data(struct dst_node *n,
+		struct dst_mirror_node_data *ndata)
+{
+	return dst_mirror_process_node_data(n, ndata, READ);
+}
+
+/*
+ * This function writes node's private data from underlying media.
+ */
+static int dst_mirror_write_node_data(struct dst_node *n,
+		struct dst_mirror_node_data *ndata)
+{
+	dprintk("%s: writing new age: %llx, node: %p %llu-%llu.\n",
+			__func__, ndata->age, n, n->start, n->size);
+	return dst_mirror_process_node_data(n, ndata, WRITE);
+}
+
+static int dst_mirror_process_log_on_disk(struct dst_node *n, int op)
+{
+	struct dst_mirror_priv *priv = n->priv;
+	struct dst_mirror_log *log = &priv->log;
+	int err = -ENOMEM;
+	unsigned int i;
+	struct bio *bio;
+	struct dst_mirror_ndp *cmp;
+
+	cmp = kzalloc(sizeof(struct dst_mirror_ndp), GFP_KERNEL);
+	if (!cmp)
+		goto err_out_exit;
+
+	bio = bio_alloc_bioset(GFP_NOIO, 1, dst_mirror_bio_set);
+	if (!bio)
+		goto err_out_free_cmp;
+
+	bio->bi_rw = op;
+	bio->bi_private = cmp;
+	bio->bi_bdev = n->bdev;
+	bio->bi_destructor = dst_mirror_destructor;
+	bio->bi_end_io = dst_mirror_ndp_end_io;
+
+	for (i=0; i<log->nr_pages; ++i) {
+		bio->bi_sector = n->size + to_sector(i*PAGE_SIZE);
+
+		err = bio_add_pc_page(n->st->queue, bio,
+				virt_to_page(log->entries[i]), PAGE_SIZE,
+				offset_in_page(log->entries[i]));
+		if (err <= 0)
+			goto err_out_free_bio;
+
+		init_completion(&cmp->complete);
+
+		if (n->bdev) {
+			generic_make_request(bio);
+		} else {
+			struct dst_request req;
+
+			memset(&req, 0, sizeof(struct dst_request));
+			dst_fill_request(&req, bio, bio->bi_sector, n,
+					&dst_mirror_ndp_bio_endio);
+
+			err = req.state->ops->push(&req);
+			if (err)
+				req.bio_endio(&req, err);
+		}
+
+		dprintk("%s: waiting for completion: bio: %p, cmp: %p.\n",
+			__func__, bio, cmp);
+
+		wait_for_completion(&cmp->complete);
+		if (cmp->err) {
+			err = cmp->err;
+			goto err_out_free_bio;
+		}
+	}
+
+	err = dst_mirror_write_node_data(n, &priv->data);
+	if (err)
+		goto err_out_free_cmp;
+
+err_out_free_bio:
+	bio_put(bio);
+err_out_free_cmp:
+	kfree(cmp);
+err_out_exit:
+	if (err)
+		dst_mirror_mark_notsync(n);
+	return err;
+}
+
+static int dst_mirror_ndp_setup(struct dst_node *n, int first_node, int clean_on_sync)
+{
+	struct dst_mirror_priv *p = n->priv;
+	int sync = 1, err;
+	struct dst_mirror_priv *fp = p;
+	struct dst_node *first;
+
+	p->full_resync = 0;
+
+	if (first_node) {
+		u64 new_age = *(u64 *)&n->st;
+
+		p->old_age = p->data.age;
+		printk(KERN_NOTICE "%s: first age: %llx -> %llx. "
+			"Old will be set to new for the first node.\n",
+				__func__, p->old_age, new_age);
+		p->data.age = new_age;
+
+		err = dst_mirror_write_node_data(n, &p->data);
+		if (err)
+			return err;
+	} else {
+		mutex_lock(&n->st->tree_lock);
+		first = dst_storage_tree_search(n->st, n->start);
+		if (!first) {
+			mutex_unlock(&n->st->tree_lock);
+			dprintk("%s: there are no nodes in the storage.\n", __func__);
+			return -ENODEV;
+		}
+
+		fp = first->priv;
+
+		if (fp->old_age != p->data.age) {
+			p->full_resync = 1;
+			sync = 0;
+		}
+
+		p->old_age = fp->old_age;
+
+		n->shared_head = first;
+		atomic_inc(&first->shared_num);
+		list_add_tail(&n->shared, &first->shared);
+		mutex_unlock(&n->st->tree_lock);
+
+		if (sync) {
+			unsigned long flags;
+			unsigned int pidx, pnum;
+
+			err = dst_mirror_process_log_on_disk(n, READ);
+			if (err)
+				goto err_out_put;
+
+			spin_lock_irqsave(&fp->log_lock, flags);
+			if (fp->data.write_idx != p->data.write_idx)
+				sync = 0;
+			spin_unlock_irqrestore(&fp->log_lock, flags);
+			
+			pnum = p->data.resync_idx / DST_LOG_ENTRIES_PER_PAGE;
+			pidx = p->data.resync_idx % DST_LOG_ENTRIES_PER_PAGE;
+
+			if (p->log.entries[pnum][pidx].error)
+				sync = 0;
+		}
+	}
+
+	if (!sync) {
+		printk(KERN_NOTICE "%s: node %llu:%llu is not synced with the first one: "
+					"first_age: %llx, new_age: %llx, indexes %s.\n",
+					__func__, n->start, n->start+n->size,
+					p->data.age, p->old_age,
+					p->full_resync ? "does not match" : "match");
+		dst_mirror_mark_notsync(n);
+	} else {
+	       	if (clean_on_sync)
+			dst_mirror_mark_node_sync(n);
+		complete(&p->resync_complete);
+
+		printk(KERN_NOTICE "%s: node %llu:%llu is in sync with the first node.\n",
+				__func__, n->start, n->start+n->size);
+	}
+
+	dprintk("%s: age: old: %llx, new: %llx.\n", __func__, p->old_age, fp->data.age);
+
+	return 0;
+
+err_out_put:
+	first = n->shared_head;
+	atomic_dec(&first->shared_num);
+	mutex_lock(&n->st->tree_lock);
+	list_del(&n->shared);
+	n->shared_head = NULL;
+	mutex_unlock(&n->st->tree_lock);
+	dst_node_put(first);
+
+	return err;
+}
+
+static int dst_mirror_end_io(struct bio *bio, unsigned int size, int err)
+{
+	struct dst_request *req = bio->bi_private;
+
+	if (bio->bi_size)
+		return 0;
+
+	dprintk("%s: req: %p, bio: %p, req->bio: %p, err: %d.\n",
+			__func__, req, bio, req->bio, err);
+	req->bio_endio(req, err);
+	bio_put(bio);
+	return 0;
+}
+
+static int dst_mirror_process_request_nosync(struct dst_request *req,
+		struct dst_node *n)
+{
+	int err = 0;
+
+	/*
+	 * Block layer requires to clone a bio.
+	 */
+	if (n->bdev) {
+		struct bio *clone = bio_alloc_bioset(GFP_NOIO,
+			req->bio->bi_max_vecs, dst_mirror_bio_set);
+
+		__bio_clone(clone, req->bio);
+
+		clone->bi_bdev = n->bdev;
+		clone->bi_destructor = dst_mirror_destructor;
+		clone->bi_private = req;
+		clone->bi_end_io = &dst_mirror_end_io;
+
+		dprintk("%s: clone: %p, bio: %p, req: %p.\n",
+				__func__, clone, req->bio, req);
+
+		generic_make_request(clone);
+		err = 1;
+	} else {
+		struct dst_request nr;
+		/*
+		 * Network state processing engine will clone request
+		 * by itself if needed. We can not use the same structure
+		 * here, since number of its fields will be modified.
+		 */
+		memcpy(&nr, req, sizeof(struct dst_request));
+
+		nr.node = n;
+		nr.state = n->state;
+		nr.priv = req;
+
+		err = kst_check_permissions(n->state, req->bio);
+		if (!err)
+			err = n->state->ops->push(&nr);
+	}
+
+	dprintk("%s: req: %p, n: %p, bdev: %p, err: %d.\n",
+			__func__, req, n, n->bdev, err);
+
+	return err;
+}
+
+static int dst_mirror_sync_requeue(struct dst_node *n, int exiting)
+{
+	struct dst_mirror_priv *p = n->priv;
+	struct dst_mirror_sync_container *sc;
+	struct dst_request req;
+	unsigned long flags;
+	int err, num = 0;
+
+	if (!list_empty(&p->backlog_list))
+		dprintk("%s: n: %p, backlog_empty: %d, resync_num: %d.\n",
+			__func__, n, list_empty(&p->backlog_list),
+			atomic_read(&p->resync_num));
+
+	while (!list_empty(&p->backlog_list)) {
+		sc = NULL;
+		spin_lock_irqsave(&p->backlog_lock, flags);
+		if (!list_empty(&p->backlog_list)) {
+			sc = list_entry(p->backlog_list.next,
+					struct dst_mirror_sync_container,
+					sync_entry);
+			if (bio_rw(sc->bio) == WRITE)
+				list_del(&sc->sync_entry);
+			else
+				sc = NULL;
+		}
+		spin_unlock_irqrestore(&p->backlog_lock, flags);
+
+		if (!sc)
+			break;
+
+		sc->bio->bi_private = n;
+		if (sc->bio->bi_size == 0 || exiting) {
+			err = -EIO;
+			goto out;
+		}
+
+		memset(&req, 0, sizeof(struct dst_request));
+		dst_fill_request(&req, sc->bio, sc->start - n->start,
+				n, &kst_bio_endio);
+
+		err = dst_mirror_process_request_nosync(&req, n);
+out:
+		if (err < 0)
+			bio_endio(sc->bio, sc->bio->bi_size, err);
+		kfree(sc);
+		num++;
+	}
+
+	return num;
+}
+
+
+static void dst_mirror_resync_work(struct work_struct *work)
+{
+	struct dst_mirror_priv *priv = container_of(work,
+			struct dst_mirror_priv, resync_work.work);
+	struct dst_node *n = priv->node;
+
+	dst_mirror_resync(n, 0);
+	dst_mirror_sync_requeue(n, 0);
+	schedule_delayed_work(&priv->resync_work, priv->resync_timeout);
+}
+
+/*
+ * Mirroring log is used to store write request information.
+ * It is allocated on disk and in memory (sync happens each time
+ * resync work queue fires), and eats about 1% of free RAM or disk
+ * (what is less). Each write updates log, so when node goes offline,
+ * its log will be updated with error values, so that this entries
+ * could be resynced when node will be back online. When number of
+ * failed writes becomes equal to number of entries in the write log,
+ * recovery becomes impossible (since old log entries were overwritten)
+ * and full resync is scheduled. 
+ *
+ * This does not work well with the situation, when there are multiple
+ * writes to the same locations - they are considered as different
+ * writes and thus will be resynced multiple times.
+ * The right solution is to check log for each write, better if log
+ * would be not array, but tree.
+ */
+static int dst_mirror_log_init(struct dst_node *n)
+{
+	struct dst_mirror_priv *priv = n->priv;
+	struct dst_mirror_log *log = &priv->log;
+	struct dst_mirror_node_data *pd = &priv->data;
+	u64 allowed_ram = DIV_ROUND_UP(global_page_state(NR_FREE_PAGES), 100);
+	u64 allowed_disk = DIV_ROUND_UP(to_bytes(n->size), 100);
+	u64 num;
+	unsigned int nr_pages, i;
+	int err;
+
+	err = dst_mirror_read_node_data(n, pd);
+	if (err)
+		return err;
+
+	allowed_ram <<= PAGE_SHIFT;
+
+	num = min(allowed_disk, allowed_ram)/sizeof(struct dst_write_entry);
+	nr_pages = min(allowed_disk, allowed_ram) >> PAGE_SHIFT;
+
+	log->entries = kzalloc(nr_pages * sizeof(void *), GFP_KERNEL);
+	if (!log->entries)
+		return -ENOMEM;
+
+	for (i=0; i<nr_pages; ++i) {
+		log->entries[i] = kzalloc(PAGE_SIZE, GFP_KERNEL);
+		if (!log->entries[i])
+			goto err_out_free;
+	}
+
+	log->nr_pages = nr_pages;
+
+	pd->num = num;
+	pd->write_idx = pd->resync_idx = 0;
+
+	printk(KERN_INFO "%s: mirror write log contains %llu entries (%u pages).\n",
+			__func__, num, nr_pages);
+
+	return 0;
+
+err_out_free:
+	while (i-- != 0)
+		kfree(log->entries[i]);
+	kfree(log->entries);
+
+	return -ENOMEM;
+}
+
+static void dst_mirror_log_exit(struct dst_node *n)
+{
+	struct dst_mirror_priv *priv = n->priv;
+	unsigned int i;
+
+	for (i=0; i<priv->log.nr_pages; ++i)
+		kfree(priv->log.entries[i]);
+	kfree(priv->log.entries);
+}
+
+/*
+ * This callback is invoked when node is added to storage.
+ */
+static int dst_mirror_add_node(struct dst_node *n)
+{
+	struct dst_storage *st = n->st;
+	struct dst_mirror_priv *priv;
+	int err = -ENOMEM, first_node = 0;
+	u64 disk_size;
+
+	n->size--; /* A sector size actually. */
+
+	priv = kzalloc(sizeof(struct dst_mirror_priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->ndp_sector = n->size;
+	priv->node = n;
+	priv->resync_start = 0;
+	priv->resync_size = to_sector(1024*1024*100ULL);
+	init_completion(&priv->resync_complete);
+	atomic_set(&priv->resync_num, 0);
+	INIT_DELAYED_WORK(&priv->resync_work, dst_mirror_resync_work);
+	priv->resync_timeout = 1000;
+
+	spin_lock_init(&priv->resync_wait_lock);
+	INIT_LIST_HEAD(&priv->resync_wait_list);
+	priv->resync_wait_num = 0;
+
+	spin_lock_init(&priv->backlog_lock);
+	INIT_LIST_HEAD(&priv->backlog_list);
+
+	n->priv_callback = &dst_mirror_handle_priv;
+	n->priv = priv;
+
+	spin_lock_init(&priv->log_lock);
+	
+	err = dst_mirror_log_init(n);
+	if (err)
+		goto err_out_free;
+
+	n->size -= to_sector(priv->log.nr_pages << PAGE_SHIFT);
+
+	mutex_lock(&st->tree_lock);
+	disk_size = st->disk_size;
+	if (st->disk_size) {
+		st->disk_size = min(n->size, st->disk_size);
+	} else {
+		st->disk_size = n->size;
+		first_node = 1;
+	}
+	mutex_unlock(&st->tree_lock);
+
+	err = dst_mirror_ndp_setup(n, first_node, 1);
+	if (err)
+		goto err_out_free_log;
+
+	schedule_delayed_work(&priv->resync_work, priv->resync_timeout);
+
+	dprintk("%s: n: %p, %llu:%llu, disk_size: %llu.\n",
+		__func__, n, n->start, n->size, st->disk_size);
+
+	return 0;
+
+err_out_free_log:
+	mutex_lock(&st->tree_lock);
+	st->disk_size = disk_size;
+	mutex_unlock(&st->tree_lock);
+	dst_mirror_log_exit(n);
+err_out_free:
+	kfree(priv);
+	n->priv = NULL;
+	return err;
+}
+
+static void dst_mirror_sync_destructor(struct bio *bio)
+{
+	struct bio_vec *bv;
+	int i;
+
+	bio_for_each_segment(bv, bio, i)
+		__free_page(bv->bv_page);
+	bio_free(bio, dst_mirror_bio_set);
+}
+
+static void dst_mirror_check_resync_complete(struct dst_node *n, int num_completed)
+{
+	struct dst_mirror_priv *priv = n->priv;
+
+	if (atomic_sub_return(num_completed, &priv->resync_num) == 0) {
+		dprintk("%s: completing resync request, start: %llu, size: %llu.\n",
+				__func__, priv->resync_start, priv->resync_size);
+		complete(&priv->resync_complete);
+		if (!priv->full_resync)
+			schedule_delayed_work(&priv->resync_work, 0);
+	}
+}
+
+static int dst_mirror_sync_check(struct dst_node *n)
+{
+	struct dst_mirror_priv *priv = n->priv;
+	struct dst_mirror_node_data *pd = &priv->data;
+	unsigned int pidx, pnum, i, j;
+	struct dst_write_entry *e;
+
+	pnum = pd->resync_idx / DST_LOG_ENTRIES_PER_PAGE;
+	pidx = pd->resync_idx % DST_LOG_ENTRIES_PER_PAGE;
+
+	for (i=pnum; i<priv->log.nr_pages; ++i) {
+		for (j=pidx; j<DST_LOG_ENTRIES_PER_PAGE; ++j) {
+			e = &priv->log.entries[i][j];
+
+			if (e->error) {
+				pd->resync_idx = i*DST_LOG_ENTRIES_PER_PAGE + j;
+				return 1;
+			}
+		}
+
+		pidx = 0;
+	}
+
+	dst_mirror_mark_node_sync(n);
+	return 0;
+}
+
+static int dst_mirror_sync_endio(struct bio *bio, unsigned int size, int err)
+{
+	dprintk("%s: bio: %p, err: %d, size: %u, op: %s.\n",
+			__func__, bio, err, bio->bi_size,
+			(bio_rw(bio) != WRITE)?"read":"write");
+
+	if (bio->bi_size)
+		return 1;
+
+	if (bio_rw(bio) != WRITE) {
+		struct dst_mirror_sync_container *sc = bio->bi_private;
+
+		if (err)
+			dst_mirror_mark_notsync(sc->node);
+
+		if (!err) {
+			bio->bi_size = sc->size;
+			bio->bi_sector = sc->start;
+		}
+		bio->bi_rw = WRITE;
+	} else {
+		struct dst_node *n = bio->bi_private;
+		struct dst_mirror_priv *priv = n->priv;
+		
+		if (err)
+			dst_mirror_mark_notsync(n);
+		else if (!priv->full_resync) {
+			struct dst_mirror_node_data *pd = &priv->data;
+			unsigned long flags;
+
+			spin_lock_irqsave(&priv->log_lock, flags);
+			pd->resync_idx = (pd->resync_idx + 1) % pd->num;
+			dst_mirror_sync_check(n);
+			spin_unlock_irqrestore(&priv->log_lock, flags);
+		}
+		bio_put(bio);
+		dst_mirror_check_resync_complete(n, 1);
+	}
+
+	return 0;
+}
+
+static int dst_mirror_sync_block(struct dst_node *n,
+		u64 start, u32 size)
+{
+	struct bio *bio;
+	unsigned int nr_pages = DIV_ROUND_UP(size, PAGE_SIZE), i, nr;
+	struct page *page;
+	int err = -ENOMEM;
+	unsigned long flags;
+	struct dst_mirror_sync_container *sc;
+	struct dst_mirror_priv *priv = n->priv;
+
+	dprintk("%s: [all in sectors] start: %llu, size: %u, nr_pages: %u, disk_size: %llu.\n",
+			__func__, (u64)to_sector(start), (unsigned int)to_sector(size),
+			nr_pages, n->st->disk_size);
+
+	atomic_set(&priv->resync_num, nr_pages);
+
+	while (nr_pages) {
+		nr = min_t(unsigned int, nr_pages, BIO_MAX_PAGES);
+
+		sc = kmalloc(sizeof(struct dst_mirror_sync_container), GFP_KERNEL);
+		if (!sc)
+			return -ENOMEM;
+
+		bio = bio_alloc_bioset(GFP_NOIO, nr, dst_mirror_bio_set);
+		if (!bio)
+			goto err_out_free_sc;
+
+		bio->bi_rw = READ;
+		bio->bi_private = sc;
+		bio->bi_sector = to_sector(start);
+		bio->bi_bdev = NULL;
+		bio->bi_destructor = dst_mirror_sync_destructor;
+		bio->bi_end_io = dst_mirror_sync_endio;
+
+		for (i = 0; i < nr; ++i) {
+			page = alloc_page(GFP_NOIO);
+			if (!page)
+				break;
+
+			err = bio_add_pc_page(n->st->queue, bio, page,
+					min_t(u32, PAGE_SIZE, size), 0);
+			if (err <= 0)
+				break;
+			size -= err;
+			err = 0;
+		}
+
+		if (!bio->bi_vcnt) {
+			err = -ENOMEM;
+			goto err_out_put_bio;
+		}
+
+		sc->node = n;
+		sc->bio = bio;
+		sc->start = bio->bi_sector;
+		sc->size = bio->bi_size;
+
+		dst_mirror_check_resync_complete(n, i-1);
+
+		spin_lock_irqsave(&priv->backlog_lock, flags);
+		list_add_tail(&sc->sync_entry, &priv->backlog_list);
+		spin_unlock_irqrestore(&priv->backlog_lock, flags);
+
+		nr_pages -= bio->bi_vcnt;
+		dprintk("%s: start: %llu, size: %u/%u, bio: %p, rest_pages: %u, rest_bytes: %u.\n",
+			__func__, start, bio->bi_size, nr, bio, nr_pages, size);
+
+		start += bio->bi_size;
+
+		err = n->st->queue->make_request_fn(n->st->queue, bio);
+		if (err)
+			goto err_out_del;
+	}
+
+	return 0;
+
+err_out_del:
+	spin_lock_irqsave(&priv->backlog_lock, flags);
+	list_del(&sc->sync_entry);
+	spin_unlock_irqrestore(&priv->backlog_lock, flags);
+err_out_put_bio:
+	bio_put(bio);
+err_out_free_sc:
+	kfree(sc);
+	return err;
+}
+
+static void dst_mirror_read_endio(struct dst_request *req, int err)
+{
+	if (err)
+		dst_mirror_mark_notsync(req->node);
+
+	if (err && req->state)
+		kst_wake(req->state);
+
+	if (!err || req->callback)
+		kst_bio_endio(req, err);
+}
+
+static void dst_mirror_update_write_log(struct dst_request *req, int err)
+{
+	struct dst_mirror_priv *priv = req->node->priv;
+	struct dst_mirror_log *log = &priv->log;
+	struct dst_mirror_node_data *pd = &priv->data;
+	unsigned long flags;
+	struct dst_write_entry *e;
+	unsigned int pnum, idx;
+
+	spin_lock_irqsave(&priv->log_lock, flags);
+
+	pnum = pd->write_idx / DST_LOG_ENTRIES_PER_PAGE;
+	idx = pd->write_idx % DST_LOG_ENTRIES_PER_PAGE;
+
+	e = &log->entries[pnum][idx];
+	e->error = err;
+	e->start = req->start - to_sector(req->orig_size);
+	e->size = req->orig_size;
+
+	if (++pd->write_idx == pd->num)
+		pd->write_idx = 0;
+
+	if (test_bit(DST_NODE_NOTSYNC, &req->node->flags) &&
+			pd->write_idx == pd->resync_idx)
+		priv->full_resync = 1;
+
+	spin_unlock_irqrestore(&priv->log_lock, flags);
+}
+
+static void dst_mirror_write_endio(struct dst_request *req, int err)
+{
+	if (err) {
+		dst_mirror_mark_notsync(req->node);
+		if (req->state)
+			kst_wake(req->state);
+	}
+	dst_mirror_update_write_log(req, err);
+
+	req = req->priv;
+
+	dprintk("%s: req: %p, priv: %p err: %d, bio: %p, "
+			"cnt: %d, orig_size: %llu.\n",
+		__func__, req, req->priv, err, req->bio,
+		atomic_read(&req->refcnt), req->orig_size);
+
+	if (atomic_dec_and_test(&req->refcnt)) {
+		bio_endio(req->bio, req->orig_size, 0);
+		dst_free_request(req);
+	}
+}
+
+static int dst_mirror_process_request(struct dst_request *req,
+		struct dst_node *n)
+{
+	int err;
+
+	dst_mirror_sync_requeue(n, 0);
+	err = dst_mirror_process_request_nosync(req, n);
+	if (err > 0)
+		err = 0;
+	if (err)
+		req->bio_endio(req, err);
+
+	return err;
+}
+
+static int dst_mirror_write(struct dst_request *oreq)
+{
+	struct dst_node *n, *node = oreq->node;
+	struct dst_request *req = oreq;
+	int num, err = 0, err_num = 0, orig_num;
+	struct dst_mirror_priv *priv = node->priv;
+	unsigned long flags;
+
+	/*
+	 * This check is for requests which fell into resync window.
+	 * Such requests are written when resync window moves forward.
+	 */
+	if (oreq->bio_endio != &dst_mirror_write_endio) {
+		req = dst_clone_request(oreq, oreq->node->w->req_pool);
+		if (!req) {
+			err = -ENOMEM;
+			goto err_out_exit;
+		}
+
+		req->priv = req;
+		req->bio_endio = &dst_mirror_write_endio;
+	}
+
+	if (test_bit(DST_NODE_NOTSYNC, &node->flags) &&
+			oreq->start >= priv->resync_start &&
+			to_sector(oreq->orig_size) <= priv->resync_size &&
+			priv->full_resync) {
+		dprintk("%s: queueing request: start: %llu, size: %llu, resync window start: %llu, size: %llu.\n",
+				__func__, oreq->start, (u64)to_sector(oreq->orig_size),
+				priv->resync_start, priv->resync_size);
+		spin_lock_irqsave(&priv->resync_wait_lock, flags);
+		list_add_tail(&req->request_list_entry, &priv->resync_wait_list);
+		priv->resync_wait_num++;
+		spin_unlock_irqrestore(&priv->resync_wait_lock, flags);
+		return 0;
+	}
+
+	/*
+	 * This logic is pretty simple - req->bio_endio will not
+	 * call bio_endio() until all mirror devices completed
+	 * processing of the request (no matter with or without error).
+	 * Mirror's req->bio_endio callback will take care of that.
+	 */
+	orig_num = num = atomic_read(&req->node->shared_num) + 1;
+	atomic_set(&req->refcnt, num);
+
+	dprintk("\n%s: req: %p, mirror to %d nodes.\n",
+			__func__, req, num);
+
+	err = dst_mirror_process_request(req, node);
+	if (err)
+		err_num++;
+
+	if (--num) {
+		list_for_each_entry(n, &node->shared, shared) {
+			dprintk("\n%s: req: %p, start: %llu, size: %llu, "
+					"num: %d, n: %p, state: %p.\n",
+				__func__, req, req->start,
+				req->size, num, n, n->state);
+
+			err = dst_mirror_process_request(req, n);
+			if (err)
+				err_num++;
+
+			if (--num <= 0)
+				break;
+		}
+	}
+
+	if (err_num == orig_num)
+		dprintk("%s: req: %p, num: %d, err: %d.\n",
+				__func__, req, num, err);
+
+	err = 0;
+
+err_out_exit:
+	return err;
+}
+
+static int dst_mirror_read(struct dst_request *req)
+{
+	struct dst_node *node = req->node, *n, *min_dist_node;
+	struct dst_mirror_priv *priv = node->priv;
+	u64 dist, d;
+	int err;
+
+	req->bio_endio = &dst_mirror_read_endio;
+
+	do {
+		err = -ENODEV;
+		min_dist_node = NULL;
+		dist = -1ULL;
+
+		/*
+		 * Reading is never performed from the node under resync.
+		 */
+
+		if (!test_bit(DST_NODE_NOTSYNC, &node->flags)) {
+			priv = node->priv;
+			if (req->start > priv->last_start)
+				dist = req->start - priv->last_start;
+			else
+				dist = priv->last_start - req->start;
+			min_dist_node = req->node;
+		}
+
+		list_for_each_entry(n, &node->shared, shared) {
+			if (test_bit(DST_NODE_NOTSYNC, &n->flags))
+				continue;
+
+			priv = n->priv;
+
+			if (req->start > priv->last_start)
+				d = req->start - priv->last_start;
+			else
+				d = priv->last_start - req->start;
+
+			if (d < dist)
+				min_dist_node = n;
+		}
+
+		if (!min_dist_node)
+			break;
+
+		priv = min_dist_node->priv;
+		priv->last_start = req->start;
+
+		req->node = min_dist_node;
+		req->state = req->node->state;
+
+		if (req->node->bdev) {
+			req->bio->bi_bdev = req->node->bdev;
+			generic_make_request(req->bio);
+			err = 0;
+			break;
+		}
+
+		err = req->state->ops->push(req);
+		if (err) {
+			dprintk("%s: req: %p, bio: %p, node: %p, err: %d.\n",
+				__func__, req, req->bio, min_dist_node, err);
+			dst_mirror_mark_notsync(req->node);
+		}
+	} while (err && min_dist_node);
+
+	if (err || !min_dist_node) {
+		dprintk("%s: req: %p, bio: %p, node: %p, err: %d.\n",
+			__func__, req, req->bio, min_dist_node, err);
+		if (!err)
+			err = -ENODEV;
+	}
+	dprintk("%s: req: %p, err: %d.\n", __func__, req, err);
+	return err;
+}
+
+/*
+ * This callback is invoked from block layer request processing function,
+ * its task is to remap block request to different nodes.
+ */
+static int dst_mirror_remap(struct dst_request *req)
+{
+	int (*remap[])(struct dst_request *) =
+		{&dst_mirror_read, &dst_mirror_write};
+
+	return remap[bio_rw(req->bio) == WRITE](req);
+}
+
+static void dst_mirror_write_queued(struct dst_node *n)
+{
+	struct dst_mirror_priv *priv = n->priv;
+	unsigned long flags;
+	struct dst_request *req;
+	int num = priv->resync_wait_num, err;
+
+	while (!list_empty(&priv->resync_wait_list) && num != 0) {
+		req = NULL;
+		spin_lock_irqsave(&priv->resync_wait_lock, flags);
+		if (!list_empty(&priv->resync_wait_list)) {
+			req = list_entry(priv->resync_wait_list.next,
+					struct dst_request,
+					request_list_entry);
+			list_del_init(&req->request_list_entry);
+			num--;
+		}
+		spin_unlock_irqrestore(&priv->resync_wait_lock, flags);
+
+		if (!req)
+			break;
+
+		dprintk("%s: queued request n: %p, req: %p, start: %llu, size: %llu, num: %d.\n",
+				__func__, n, req, req->start, (u64)to_sector(req->size), num);
+		err = dst_mirror_process_request(req, n);
+		if (err)
+			break;
+	}
+}
+
+static int dst_mirror_resync_partial(struct dst_node *node)
+{
+	struct dst_storage *st = node->st;
+	struct dst_node *first = node->shared_head, *n, *sync;
+	struct dst_mirror_priv *p = node->priv, *sp;
+	struct dst_mirror_node_data *pd = &p->data;
+	struct dst_mirror_node_data *spd;
+	struct dst_write_entry *e, *ep;
+	unsigned long flags;
+	unsigned int pnum, idx;
+	u64 start;
+	u32 size;
+
+	if (!first)
+		first = node;
+
+	sync = NULL;
+	mutex_lock(&st->tree_lock);
+	list_for_each_entry(n, &first->shared, shared) {
+		if (!test_bit(DST_NODE_NOTSYNC, &n->flags)) {
+			sync = n;
+			dst_node_get(sync);
+			break;
+		}
+	}
+	mutex_unlock(&st->tree_lock);
+	dprintk("%s: n: %p, first: %p, sync: %p.\n", __func__, node, first, sync);
+
+	if (!sync)
+		return -ENODEV;
+
+	sp = sync->priv;
+	spd = &sp->data;
+
+	spin_lock_irqsave(&sp->log_lock, flags);
+	spin_lock(&p->log_lock);
+
+	pnum = pd->resync_idx / DST_LOG_ENTRIES_PER_PAGE;
+	idx = pd->resync_idx % DST_LOG_ENTRIES_PER_PAGE;
+
+	ep = sp->log.entries[pnum];
+	e = &ep[idx];
+
+	start = e->start;
+	size = e->size;
+
+	spin_unlock(&p->log_lock);
+	spin_unlock_irqrestore(&sp->log_lock, flags);
+
+	dprintk("%s: node write_idx: %llu, resync_idx: %llu, num: %llu, sync write_idx: %llu, num: %llu.\n",
+			__func__, pd->write_idx, pd->resync_idx, pd->num, spd->write_idx, spd->num);
+	dprintk("%s: sync request: start: %llu, size: %llu.\n",
+			__func__, start, (u64)to_sector(size));
+
+	dst_node_put(sync);
+
+	return dst_mirror_sync_block(node, to_bytes(start), size);
+}
+
+/*
+ * Resync logic - sliding window algorithm.
+ *
+ * At startup system checks age (unique cookie) of the node and if it
+ * does not match first node it resyncs all data from the first node in
+ * the mirror to others (non-sync nodes), each non-synced node has a
+ * window, which slides from the start of the node to the end. 
+ * During resync all requests, which enter the window are queued, thus
+ * window has to be sufficiently small. When window is synced from the
+ * other nodes, queued requests are written and window moves forward,
+ * thus subsequent resync is started when previous window is fully completed.
+ * When window reaches end of the node, it is marked as synchronized.
+ *
+ * If age of the node matches the first one, but log contains different
+ * number of write log entries compared to the first node (first node always
+ * stands as a clean), then partial resync is scheduled.
+ * Partial resync will also be scheduled when log entry pointed by resync
+ * index of the node contains error.
+ *
+ * Mechanism of this resync type is following: system selects a sync node
+ * (checking each node's flags) and fetches a log entry pointed by resync
+ * index of the given node and resync data from other nodes to given one.
+ * Then it checks the rest of the write log and checks if there are
+ * another failed writes, so that next resync block would be fetched for
+ * them.
+ */
+static int dst_mirror_resync(struct dst_node *n, int ndp)
+{
+	struct dst_mirror_priv *priv = n->priv;
+	struct dst_mirror_priv *fp = priv;
+	u64 total, allowed, size;
+	int err;
+	
+	if (n->shared_head)
+		fp = n->shared_head->priv;
+
+	if (!test_bit(DST_NODE_NOTSYNC, &n->flags))
+		return 0;
+	if (atomic_read(&priv->resync_num) != 0) {
+		dprintk("%s: n: %p, resync_num: %d.\n",
+			__func__, n, atomic_read(&priv->resync_num));
+		return -EAGAIN;
+	}
+
+	allowed = global_page_state(NR_FREE_PAGES) +
+		global_page_state(NR_FILE_PAGES);
+	allowed /= 2;
+	allowed = to_sector(allowed << PAGE_SHIFT);
+
+	size = min(priv->resync_size, n->size - priv->resync_start);
+
+	total = min(allowed, size);
+
+	printk(KERN_NOTICE "%s: node: %p, %llu:%llu %s synchronization has been started "
+			"from %llu, allowed: %llu, total: %llu.\n",
+			__func__, n, n->start, n->size,
+			(priv->data.age == fp->data.age) ? "partial" : "full",
+			priv->resync_start, allowed, total);
+
+	if (!priv->full_resync)
+		return dst_mirror_resync_partial(n);
+
+	dst_mirror_write_queued(n);
+
+	if (priv->resync_start == n->size) {
+		dst_mirror_mark_node_sync(n);
+		priv->data.age = fp->data.age;
+		dst_mirror_write_node_data(n, &priv->data);
+		return 0;
+	}
+
+	if (ndp) {
+		err = dst_mirror_ndp_setup(n, 0, 0);
+		if (err)
+			return err;
+	}
+
+	err = dst_mirror_sync_block(n, to_bytes(priv->resync_start),
+			to_bytes(total));
+	if (!err)
+		priv->resync_start += total;
+
+	return err;
+}
+
+static int dst_mirror_error(struct kst_state *st, int err)
+{
+	struct dst_request *req, *tmp;
+	unsigned int revents = st->socket->ops->poll(NULL, st->socket, NULL);
+
+	dprintk("%s: err: %d, revents: %x, notsync: %d.\n",
+			__func__, err, revents,
+			test_bit(DST_NODE_NOTSYNC, &st->node->flags));
+
+	if (err == -EEXIST)
+		return err;
+
+	if (!(revents & (POLLERR | POLLHUP)) &&
+		   	(err == -EPIPE || err == -ECONNRESET)) {
+		if (test_bit(DST_NODE_NOTSYNC, &st->node->flags))
+			return dst_mirror_resync(st->node, 1);
+		return 0;
+	}
+
+	if (atomic_read(&st->node->shared_num) == 0 &&
+			!st->node->shared_head) {
+		dprintk("%s: this node is the only one in the mirror, "
+				"can not mark it notsync.\n", __func__);
+		return err;
+	}
+
+	dst_mirror_mark_notsync(st->node);
+
+	mutex_lock(&st->request_lock);
+	list_for_each_entry_safe(req, tmp, &st->request_list,
+					request_list_entry) {
+		kst_del_req(req);
+		dprintk("%s: requeue [%c], start: %llu, idx: %d,"
+				" num: %d, size: %llu, offset: %u, err: %d.\n",
+			__func__, (bio_rw(req->bio) == WRITE)?'W':'R',
+			req->start, req->idx, req->num, req->size,
+			req->offset, err);
+
+		if (bio_rw(req->bio) != WRITE) {
+			req->start -= to_sector(req->orig_size - req->size);
+			req->size = req->orig_size;
+			req->flags &= ~(DST_REQ_HEADER_SENT | DST_REQ_CHEKSUM_RECV);
+			req->idx = 0;
+			if (dst_mirror_read(req))
+				dst_free_request(req);
+		} else {
+			kst_complete_req(req, err);
+		}
+	}
+	mutex_unlock(&st->request_lock);
+	return err;
+}
+
+/*
+ * This callback is invoked when node is removed from storage.
+ */
+static void dst_mirror_del_node(struct dst_node *n)
+{
+	struct dst_mirror_priv *priv = n->priv;
+
+	priv->full_resync = 1;
+	cancel_rearming_delayed_work(&priv->resync_work);
+	flush_scheduled_work();
+
+	dprintk("%s: n: %p, backlog_empty: %d, resync_num: %d.\n",
+		__func__, n, list_empty(&priv->backlog_list),
+		atomic_read(&priv->resync_num));
+
+	/*
+	 * This strange-looking loop waits until all resync read requests
+	 * are completed, this happens in dst_mirror_sync_requeue().
+	 */
+	while (atomic_read(&priv->resync_num)) {
+		dst_mirror_sync_requeue(n, 1);
+		if (printk_ratelimit())
+			dprintk("%s: n: %p, backlog_empty: %d, resync_num: %d.\n",
+				__func__, n, list_empty(&priv->backlog_list),
+				atomic_read(&priv->resync_num));
+		msleep(100);
+	}
+
+	wait_for_completion(&priv->resync_complete);
+	dst_mirror_sync_requeue(n, 1);
+
+	if (priv) {
+		dst_mirror_log_exit(n);
+		kfree(priv);
+		n->priv = NULL;
+	}
+
+	if (n->device.parent == &n->st->device) {
+		int i;
+
+		for (i=0; i<ARRAY_SIZE(dst_mirror_attrs); ++i)
+			device_remove_file(&n->device, &dst_mirror_attrs[i]);
+	}
+}
+
+static struct dst_alg_ops alg_mirror_ops = {
+	.remap		= dst_mirror_remap,
+	.add_node	= dst_mirror_add_node,
+	.del_node	= dst_mirror_del_node,
+	.error		= dst_mirror_error,
+	.owner		= THIS_MODULE,
+};
+
+static int __devinit alg_mirror_init(void)
+{
+	int err = -ENOMEM;
+
+	dst_mirror_bio_set = bioset_create(256, 256);
+	if (!dst_mirror_bio_set)
+		return -ENOMEM;
+
+	alg_mirror = dst_alloc_alg("alg_mirror", &alg_mirror_ops);
+	if (!alg_mirror)
+		goto err_out;
+
+	return 0;
+
+err_out:
+	bioset_free(dst_mirror_bio_set);
+	return err;
+}
+
+static void __devexit alg_mirror_exit(void)
+{
+	dst_remove_alg(alg_mirror);
+	bioset_free(dst_mirror_bio_set);
+}
+
+module_init(alg_mirror_init);
+module_exit(alg_mirror_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Evgeniy Polyakov <johnpol@2ka.mipt.ru>");
+MODULE_DESCRIPTION("Mirror distributed algorithm.");

Re: [1/4] DST: Distributed storage documentation.

[Kay Sievers]

On Dec 17, 2007 4:03 PM, Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote:

> +++ b/Documentation/dst/sysfs.txt
> @@ -0,0 +1,33 @@
> +This file describes sysfs files created for each storage.
> +
> +1. Per-storage files.
> +Each storage has its own dir /sysfs/devices/$storage_name,

> +2. Per-node files.
> +Node's files are located in /sysfs/devices/$storage_name/n-$start-$cookie

As already pointed out last time, you can't reference /sys/devices/ directly,
please use the path from the bus/class directory which points there.

Thanks,
Kay

Re: [0/4] DST: Distributed storage.

[David Chinner]

On Mon, Dec 17, 2007 at 06:03:38PM +0300, Evgeniy Polyakov wrote:
> DST passed all FS tests in LTP with XFS (modulo MAX_LOCK_DEPTH too low bug:
> [ 8398.605691] BUG: MAX_LOCK_DEPTH too low!
> [ 8398.609641] turning off the locking correctness validator.

Evgeniy, can you please start reporting these XFS problems you are
coming across to the XFS list (xfs@oss.sgi.com)? They may be
real issues that we need to address and we should not be hearing
about them for the first time in the release notes for a block
device project....

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group

Re: [0/4] DST: Distributed storage.

[Evgeniy Polyakov]

Hi David.

On Tue, Dec 18, 2007 at 12:00:04PM +1100, David Chinner (dgc@sgi.com) wrote:
> On Mon, Dec 17, 2007 at 06:03:38PM +0300, Evgeniy Polyakov wrote:
> > DST passed all FS tests in LTP with XFS (modulo MAX_LOCK_DEPTH too low bug:
> > [ 8398.605691] BUG: MAX_LOCK_DEPTH too low!
> > [ 8398.609641] turning off the locking correctness validator.
> 
> Evgeniy, can you please start reporting these XFS problems you are
> coming across to the XFS list (xfs@oss.sgi.com)? They may be
> real issues that we need to address and we should not be hearing
> about them for the first time in the release notes for a block
> device project....

It is not XFS as is, but lock validator warning. I just found it
working with XFS - it can be anything else: VFS, block layer, DST itself
(there is number of locks too), so I did not fill the bug against
filesystem, but pointed that some problem, probalby harmless,
exists in tested environment.

-- 
	Evgeniy Polyakov

[0/4] DST: Distributed storage: Succumbed to live ant.

[Evgeniy Polyakov]

Distributed storage: Succumbed to live ant.

I'm pleased to announce the 14'th release of the distributed
storage subsystem (DST).

DST allows to form a storage on top of local and remote nodes
and combine them into linear or mirroring setup, which in
turn can be exported to remote nodes.

This is a maintenance release only.

Short changelog:
 * do not allocate big enough address structure on stack during
	local export node initialization
	Thanks to Serge Leschinsky and Konstantin Kalin for testing.

Overall list of features of the DST can be found on project's homepage:

http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst

DST is also exported as a git tree available for clone and pull from
http://tservice.net.ru/~s0mbre/archive/dst/dst.git

Thank you.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>

[1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

Distributed storage documentation.

Algorithms used in the system, userspace interfaces
(sysfs dirs and files), design and implementation details
are described here.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


diff --git a/Documentation/dst/algorithms.txt b/Documentation/dst/algorithms.txt
new file mode 100644
index 0000000..1437a6a
--- /dev/null
+++ b/Documentation/dst/algorithms.txt
@@ -0,0 +1,115 @@
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+
+Let's briefly describe how they work.
+
+Linear algorithm.
+Simple approach of concatenating storages into single device with
+increased size is used in this algorithm. Essentially new device
+has size equal to sum of sizes of underlying nodes and nodes are
+placed one after another.
+
+  /----- Node 1 ---\                         /------ Node 3 ----\
+start              end                     start               end
+ |==================|========================|==================|
+ |                start                     end                 |
+ |                  \------- Node 2 ---------/                  |
+ |                                                              |
+start                                                          end
+ \-------------------------- DST storage ----------------------/
+
+			        /\
+			        ||
+			        ||
+
+			   IO operations
+
+			    Figure 1. 
+     3 nodes combined into single storage using linear algorithm.
+
+Mirror algorithm.
+In this algorithms nodes are placed under each other, so when
+operation comes to the first one, it can be mirrored to all
+underlying nodes. In case of reading, actual data is obtained from
+the nearest node - algoritm keeps track of previous operation
+and knows where it was stopped, so that subsequent seek to the 
+start of the new request will take the shortest time.
+Writing is always mirrored to all underlying nodes.
+
+                  IO operations
+                       ||
+                       ||
+                       \/
+
+|---------------- DST storage -------------------|
+|      prev position                             |
+|-------|------------ Node 1 --------------------|
+|                              prev pos          |
+|-------------------- Node 2 -----|--------------|
+|prev pos                                        |
+|---|---------------- Node 3 --------------------|
+
+		Figure 2.
+   3 nodes combined into single storage using mirror algorithm.
+
+Each algorithm must implement number of callbacks,
+which must be registered during initialization time.
+
+struct dst_alg_ops
+{
+	int			(*add_node)(struct dst_node *n);
+	void			(*del_node)(struct dst_node *n);
+	int 			(*remap)(struct dst_request *req);
+	int			(*error)(struct kst_state *state, int err);
+	struct module 		*owner;
+};
+
+@add_node.
+This callback is invoked when new node is being added into the storage,
+but before node is actually added into the storage, so that it could
+be accessed from it. When it is called, all appropriate initialization
+of the underlying device is already completed (system has been connected
+to remote node or got a reference to the local block device). At this
+stage algorithm can add node into private map. 
+It must return zero on success or negative value otherwise.
+
+@del_node.
+This callback is invoked when node is being deleted from the storage,
+i.e. when its reference counter hits zero. It is called before
+any cleaning is performed.
+It must return zero on success or negative value otherwise.
+
+@remap.
+This callback is invoked each time new bio hits the storage.
+Request structure contains BIO itself, pointer to the node, which originally
+stores the whole region under given IO request, and various parameters
+used by storage core to process this block request.
+It must return zero on success or negative value otherwise. It is upto
+this method to call all cleaning if remapping failed, for example it must
+call kst_bio_endio() for given callback in case of error, which in turn
+will call bio_endio(). Note, that dst_request structure provided in this
+callback is allocated on stack, so if there is a need to use it outside
+of the given function, it must be cloned (it will happen automatically
+in state's push callback, but that copy will not be shared by any other
+user).
+
+@error.
+This callback is invoked for each error, which happend when processed
+requests for remote nodes or when talking to remote size
+of the local export node (state contains data related to data
+transfers over the network).
+If this function has fixed given error, it must return 0 or negative
+error value otherwise.
+
+@owner.
+This is module reference counter updated automatically by DST core.
+
+Algorithm must provide its name and above structure to the 
+dst_alloc_alg() function, which will return a reference to the newly
+created algorithm.
+To remove it, one needs to call dst_remove_alg() with given algorithm
+pointer.
diff --git a/Documentation/dst/dst.txt b/Documentation/dst/dst.txt
new file mode 100644
index 0000000..a6ea126
--- /dev/null
+++ b/Documentation/dst/dst.txt
@@ -0,0 +1,69 @@
+Distributed storage. Design and implementation.
+http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst
+
+	     Evgeniy Polyakov
+
+This document is intended to briefly describe design and
+implementation details of the distributed storage project,
+aimed to create ability to group physically and/or logically
+distributed storages into single device.
+
+Main operational unit in the storage is node. Node can represent
+either remote storage, connected to local machine, or local
+device, or storage exported to the outside of the system.
+Here goes small explaination of basic therms.
+
+Local node.
+This node is just a logical link between block device (with given
+major and minor numbers) and structure in the DST hierarchy,
+which represents number of sectors on the area, corresponding to given
+block device. it can be a disk, a device mapper node or stacked
+block device on top of another underlying DST nodes.
+
+Local export node.
+Essentially the same as local node, but it allows to access
+to its data via network. Remote clients can connect to given local 
+export node and read or write blocks according to its size.
+Blocks are then forwarded to underlying local node and processed
+there accordingly to the nature of the local node.
+
+Remote node.
+This type of nodes contain remotely accessible devices. One can think
+about remote nodes as remote disks, which can be connected to
+local system and combined into single storage. Remote nodes
+are presented as number of sectors accessed over the network
+by the local machine, where distributed storage is being formed.
+Remote node allows autoconfiguration - size of the storage and
+checksumming will be requested during node initialization (if remote
+node supports checksumming it will be turned on).
+
+
+Each node or set of them can be formed into single array, which
+in turn becomes a local node, which can be exported further by stacking
+a local export node on top of it.
+
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+One can find more details in Documentation/dst/algorithms.txt file.
+
+Main goal of the distributed storage is to combine remote nodes into
+single device, so each block IO request is being sent over the network
+(contrary requests for local nodes are handled by the gneric block
+layer features). Each network connection has number of variables which
+describe it (socket, list of requests, error handling and so on),
+which form kst_state structure. This network state is added into per-socket
+polling state machine, and can be processed by dedicated thread when
+becomes ready. This system forms asynchronous IO for given block
+requests. If block request can be processed without blocking, then
+no new structures are allocated and async part of the state is not used.
+
+When connection to the remote peer breaks, DST core tries to reconnect
+to failed node and no requests are marked as errorneous, instead
+they live in the queue until reconnectin is established.
+
+Userspace code, setup documentation and examples can be found on project's
+homepage above.
diff --git a/Documentation/dst/sysfs.txt b/Documentation/dst/sysfs.txt
new file mode 100644
index 0000000..782ada0
--- /dev/null
+++ b/Documentation/dst/sysfs.txt
@@ -0,0 +1,33 @@
+This file describes sysfs files created for each storage.
+
+1. Per-storage files.
+Each storage has its own dir /sys/bus/dst/devices/$storage_name,
+which contains following files:
+
+alg - contains name of the algorithm used to created given storage
+name - name of the storage
+nodes - map of the storage (list of nodes and their sizes and starts)
+remove_all_nodes - writable file which allows to remove all nodes from given
+	storage
+n-$start-$cookie - per node directory, where
+	$start - start of the given node in sectors,
+	$cookie - unique node's id used by DST
+
+2. Per-node files.
+Node's files are located in /sys/bus/dst/devices/$storage_name/n-$start-$cookie
+directory, described above.
+
+clean - writable file, writing leads to marking node as clean (in sync)
+dirty - writable file, writing leads to marking node as dirty (not in sync)
+resync_size - size of the resync sliding window
+resync_timout - resync requests checking timeout (in milliseconds) of
+	the background worker thread
+state - sync/notsync state of the node in the mirror
+
+flags - flags of the given node
+size - size of the given node in sectors
+start - start of the given node in the storage in sectors
+type - contains type of the node in the following format: $type: $dev
+	where $type is either 'L' or 'R' - local or remote acordingly,
+	and $dev is device name for local node (/dev/sda1 for example)
+	or address of the remote node (192.168.4.81:1025 for example)

[0/4] DST: Distributed storage: Groundhogs strike back: no New Year for humans

[Evgeniy Polyakov]

Distributed storage: Groundhogs strike back: no New Year for humans

I'm pleased to announce the 13'th release of the distributed
storage subsystem (DST).

DST allows to form a storage on top of local and remote nodes
and combine them into linear or mirroring setup, which in
turn can be exported to remote nodes.

Short changelog:
 * mirroring algorithm improvements
 * debug cleanups
 * extended mirroring initialization
 * documentation update
 * name is 'Groundhogs strike back: no New Year for humans' now

Overall list of features of the DST can be found on project's homepage:

http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst

DST is also exported as a git tree available for clone and pull from
http://tservice.net.ru/~s0mbre/archive/dst/dst.git

Thank you.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>

[1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

Distributed storage documentation.

Algorithms used in the system, userspace interfaces
(sysfs dirs and files), design and implementation details
are described here.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


diff --git a/Documentation/dst/algorithms.txt b/Documentation/dst/algorithms.txt
new file mode 100644
index 0000000..1437a6a
--- /dev/null
+++ b/Documentation/dst/algorithms.txt
@@ -0,0 +1,115 @@
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+
+Let's briefly describe how they work.
+
+Linear algorithm.
+Simple approach of concatenating storages into single device with
+increased size is used in this algorithm. Essentially new device
+has size equal to sum of sizes of underlying nodes and nodes are
+placed one after another.
+
+  /----- Node 1 ---\                         /------ Node 3 ----\
+start              end                     start               end
+ |==================|========================|==================|
+ |                start                     end                 |
+ |                  \------- Node 2 ---------/                  |
+ |                                                              |
+start                                                          end
+ \-------------------------- DST storage ----------------------/
+
+			        /\
+			        ||
+			        ||
+
+			   IO operations
+
+			    Figure 1. 
+     3 nodes combined into single storage using linear algorithm.
+
+Mirror algorithm.
+In this algorithms nodes are placed under each other, so when
+operation comes to the first one, it can be mirrored to all
+underlying nodes. In case of reading, actual data is obtained from
+the nearest node - algoritm keeps track of previous operation
+and knows where it was stopped, so that subsequent seek to the 
+start of the new request will take the shortest time.
+Writing is always mirrored to all underlying nodes.
+
+                  IO operations
+                       ||
+                       ||
+                       \/
+
+|---------------- DST storage -------------------|
+|      prev position                             |
+|-------|------------ Node 1 --------------------|
+|                              prev pos          |
+|-------------------- Node 2 -----|--------------|
+|prev pos                                        |
+|---|---------------- Node 3 --------------------|
+
+		Figure 2.
+   3 nodes combined into single storage using mirror algorithm.
+
+Each algorithm must implement number of callbacks,
+which must be registered during initialization time.
+
+struct dst_alg_ops
+{
+	int			(*add_node)(struct dst_node *n);
+	void			(*del_node)(struct dst_node *n);
+	int 			(*remap)(struct dst_request *req);
+	int			(*error)(struct kst_state *state, int err);
+	struct module 		*owner;
+};
+
+@add_node.
+This callback is invoked when new node is being added into the storage,
+but before node is actually added into the storage, so that it could
+be accessed from it. When it is called, all appropriate initialization
+of the underlying device is already completed (system has been connected
+to remote node or got a reference to the local block device). At this
+stage algorithm can add node into private map. 
+It must return zero on success or negative value otherwise.
+
+@del_node.
+This callback is invoked when node is being deleted from the storage,
+i.e. when its reference counter hits zero. It is called before
+any cleaning is performed.
+It must return zero on success or negative value otherwise.
+
+@remap.
+This callback is invoked each time new bio hits the storage.
+Request structure contains BIO itself, pointer to the node, which originally
+stores the whole region under given IO request, and various parameters
+used by storage core to process this block request.
+It must return zero on success or negative value otherwise. It is upto
+this method to call all cleaning if remapping failed, for example it must
+call kst_bio_endio() for given callback in case of error, which in turn
+will call bio_endio(). Note, that dst_request structure provided in this
+callback is allocated on stack, so if there is a need to use it outside
+of the given function, it must be cloned (it will happen automatically
+in state's push callback, but that copy will not be shared by any other
+user).
+
+@error.
+This callback is invoked for each error, which happend when processed
+requests for remote nodes or when talking to remote size
+of the local export node (state contains data related to data
+transfers over the network).
+If this function has fixed given error, it must return 0 or negative
+error value otherwise.
+
+@owner.
+This is module reference counter updated automatically by DST core.
+
+Algorithm must provide its name and above structure to the 
+dst_alloc_alg() function, which will return a reference to the newly
+created algorithm.
+To remove it, one needs to call dst_remove_alg() with given algorithm
+pointer.
diff --git a/Documentation/dst/dst.txt b/Documentation/dst/dst.txt
new file mode 100644
index 0000000..a6ea126
--- /dev/null
+++ b/Documentation/dst/dst.txt
@@ -0,0 +1,69 @@
+Distributed storage. Design and implementation.
+http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst
+
+	     Evgeniy Polyakov
+
+This document is intended to briefly describe design and
+implementation details of the distributed storage project,
+aimed to create ability to group physically and/or logically
+distributed storages into single device.
+
+Main operational unit in the storage is node. Node can represent
+either remote storage, connected to local machine, or local
+device, or storage exported to the outside of the system.
+Here goes small explaination of basic therms.
+
+Local node.
+This node is just a logical link between block device (with given
+major and minor numbers) and structure in the DST hierarchy,
+which represents number of sectors on the area, corresponding to given
+block device. it can be a disk, a device mapper node or stacked
+block device on top of another underlying DST nodes.
+
+Local export node.
+Essentially the same as local node, but it allows to access
+to its data via network. Remote clients can connect to given local 
+export node and read or write blocks according to its size.
+Blocks are then forwarded to underlying local node and processed
+there accordingly to the nature of the local node.
+
+Remote node.
+This type of nodes contain remotely accessible devices. One can think
+about remote nodes as remote disks, which can be connected to
+local system and combined into single storage. Remote nodes
+are presented as number of sectors accessed over the network
+by the local machine, where distributed storage is being formed.
+Remote node allows autoconfiguration - size of the storage and
+checksumming will be requested during node initialization (if remote
+node supports checksumming it will be turned on).
+
+
+Each node or set of them can be formed into single array, which
+in turn becomes a local node, which can be exported further by stacking
+a local export node on top of it.
+
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+One can find more details in Documentation/dst/algorithms.txt file.
+
+Main goal of the distributed storage is to combine remote nodes into
+single device, so each block IO request is being sent over the network
+(contrary requests for local nodes are handled by the gneric block
+layer features). Each network connection has number of variables which
+describe it (socket, list of requests, error handling and so on),
+which form kst_state structure. This network state is added into per-socket
+polling state machine, and can be processed by dedicated thread when
+becomes ready. This system forms asynchronous IO for given block
+requests. If block request can be processed without blocking, then
+no new structures are allocated and async part of the state is not used.
+
+When connection to the remote peer breaks, DST core tries to reconnect
+to failed node and no requests are marked as errorneous, instead
+they live in the queue until reconnectin is established.
+
+Userspace code, setup documentation and examples can be found on project's
+homepage above.
diff --git a/Documentation/dst/sysfs.txt b/Documentation/dst/sysfs.txt
new file mode 100644
index 0000000..782ada0
--- /dev/null
+++ b/Documentation/dst/sysfs.txt
@@ -0,0 +1,33 @@
+This file describes sysfs files created for each storage.
+
+1. Per-storage files.
+Each storage has its own dir /sys/bus/dst/devices/$storage_name,
+which contains following files:
+
+alg - contains name of the algorithm used to created given storage
+name - name of the storage
+nodes - map of the storage (list of nodes and their sizes and starts)
+remove_all_nodes - writable file which allows to remove all nodes from given
+	storage
+n-$start-$cookie - per node directory, where
+	$start - start of the given node in sectors,
+	$cookie - unique node's id used by DST
+
+2. Per-node files.
+Node's files are located in /sys/bus/dst/devices/$storage_name/n-$start-$cookie
+directory, described above.
+
+clean - writable file, writing leads to marking node as clean (in sync)
+dirty - writable file, writing leads to marking node as dirty (not in sync)
+resync_size - size of the resync sliding window
+resync_timout - resync requests checking timeout (in milliseconds) of
+	the background worker thread
+state - sync/notsync state of the node in the mirror
+
+flags - flags of the given node
+size - size of the given node in sectors
+start - start of the given node in the storage in sectors
+type - contains type of the node in the following format: $type: $dev
+	where $type is either 'L' or 'R' - local or remote acordingly,
+	and $dev is device name for local node (/dev/sda1 for example)
+	or address of the remote node (192.168.4.81:1025 for example)

[0/4] DST: Distributed storage.

[Evgeniy Polyakov]

Distributed storage.

I'm pleased to announce the 11'th release of the distributed
storage subsystem (DST). This is a maintenance release and includes
bug fixes and simple feature extensions only.

DST allows to form a storage on top of local and remote nodes
and combine them into linear or mirroring setup, which in
turn can be exported to remote nodes.

Short changelog:
 * wakeup state when mirror detected error to seedup reconnect
 * if connecting in csum mode to no-csum server, do not enable csums
 * do not clean queue until all users are removed
 * allow to increase size of the storage in linear add callback 
	(with this change it is possible to add nodes into linear array
	in real time without stopping storage. Filesystem has to be prepared
	for the case when underlying device has changed its size.
	Real-time addon of mirror nodes is also supported)
 * allow to delete gendisk only after device was started
 * dst debug config option
 * Name: Gamardjoba, genacvale! ('Hi friend' in georgian)

Great thanks to Matthew Hodgson <matthew@mxtelecom.com> for debugging!

Overall list of features of the DST can be found on project's homepage:

http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst

Thank you.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>

[1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

Distributed storage documentation.

Algorithms used in the system, userspace interfaces
(sysfs dirs and files), design and implementation details
are described here.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


diff --git a/Documentation/dst/algorithms.txt b/Documentation/dst/algorithms.txt
new file mode 100644
index 0000000..1437a6a
--- /dev/null
+++ b/Documentation/dst/algorithms.txt
@@ -0,0 +1,115 @@
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+
+Let's briefly describe how they work.
+
+Linear algorithm.
+Simple approach of concatenating storages into single device with
+increased size is used in this algorithm. Essentially new device
+has size equal to sum of sizes of underlying nodes and nodes are
+placed one after another.
+
+  /----- Node 1 ---\                         /------ Node 3 ----\
+start              end                     start               end
+ |==================|========================|==================|
+ |                start                     end                 |
+ |                  \------- Node 2 ---------/                  |
+ |                                                              |
+start                                                          end
+ \-------------------------- DST storage ----------------------/
+
+			        /\
+			        ||
+			        ||
+
+			   IO operations
+
+			    Figure 1. 
+     3 nodes combined into single storage using linear algorithm.
+
+Mirror algorithm.
+In this algorithms nodes are placed under each other, so when
+operation comes to the first one, it can be mirrored to all
+underlying nodes. In case of reading, actual data is obtained from
+the nearest node - algoritm keeps track of previous operation
+and knows where it was stopped, so that subsequent seek to the 
+start of the new request will take the shortest time.
+Writing is always mirrored to all underlying nodes.
+
+                  IO operations
+                       ||
+                       ||
+                       \/
+
+|---------------- DST storage -------------------|
+|      prev position                             |
+|-------|------------ Node 1 --------------------|
+|                              prev pos          |
+|-------------------- Node 2 -----|--------------|
+|prev pos                                        |
+|---|---------------- Node 3 --------------------|
+
+		Figure 2.
+   3 nodes combined into single storage using mirror algorithm.
+
+Each algorithm must implement number of callbacks,
+which must be registered during initialization time.
+
+struct dst_alg_ops
+{
+	int			(*add_node)(struct dst_node *n);
+	void			(*del_node)(struct dst_node *n);
+	int 			(*remap)(struct dst_request *req);
+	int			(*error)(struct kst_state *state, int err);
+	struct module 		*owner;
+};
+
+@add_node.
+This callback is invoked when new node is being added into the storage,
+but before node is actually added into the storage, so that it could
+be accessed from it. When it is called, all appropriate initialization
+of the underlying device is already completed (system has been connected
+to remote node or got a reference to the local block device). At this
+stage algorithm can add node into private map. 
+It must return zero on success or negative value otherwise.
+
+@del_node.
+This callback is invoked when node is being deleted from the storage,
+i.e. when its reference counter hits zero. It is called before
+any cleaning is performed.
+It must return zero on success or negative value otherwise.
+
+@remap.
+This callback is invoked each time new bio hits the storage.
+Request structure contains BIO itself, pointer to the node, which originally
+stores the whole region under given IO request, and various parameters
+used by storage core to process this block request.
+It must return zero on success or negative value otherwise. It is upto
+this method to call all cleaning if remapping failed, for example it must
+call kst_bio_endio() for given callback in case of error, which in turn
+will call bio_endio(). Note, that dst_request structure provided in this
+callback is allocated on stack, so if there is a need to use it outside
+of the given function, it must be cloned (it will happen automatically
+in state's push callback, but that copy will not be shared by any other
+user).
+
+@error.
+This callback is invoked for each error, which happend when processed
+requests for remote nodes or when talking to remote size
+of the local export node (state contains data related to data
+transfers over the network).
+If this function has fixed given error, it must return 0 or negative
+error value otherwise.
+
+@owner.
+This is module reference counter updated automatically by DST core.
+
+Algorithm must provide its name and above structure to the 
+dst_alloc_alg() function, which will return a reference to the newly
+created algorithm.
+To remove it, one needs to call dst_remove_alg() with given algorithm
+pointer.
diff --git a/Documentation/dst/dst.txt b/Documentation/dst/dst.txt
new file mode 100644
index 0000000..a6ea126
--- /dev/null
+++ b/Documentation/dst/dst.txt
@@ -0,0 +1,69 @@
+Distributed storage. Design and implementation.
+http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst
+
+	     Evgeniy Polyakov
+
+This document is intended to briefly describe design and
+implementation details of the distributed storage project,
+aimed to create ability to group physically and/or logically
+distributed storages into single device.
+
+Main operational unit in the storage is node. Node can represent
+either remote storage, connected to local machine, or local
+device, or storage exported to the outside of the system.
+Here goes small explaination of basic therms.
+
+Local node.
+This node is just a logical link between block device (with given
+major and minor numbers) and structure in the DST hierarchy,
+which represents number of sectors on the area, corresponding to given
+block device. it can be a disk, a device mapper node or stacked
+block device on top of another underlying DST nodes.
+
+Local export node.
+Essentially the same as local node, but it allows to access
+to its data via network. Remote clients can connect to given local 
+export node and read or write blocks according to its size.
+Blocks are then forwarded to underlying local node and processed
+there accordingly to the nature of the local node.
+
+Remote node.
+This type of nodes contain remotely accessible devices. One can think
+about remote nodes as remote disks, which can be connected to
+local system and combined into single storage. Remote nodes
+are presented as number of sectors accessed over the network
+by the local machine, where distributed storage is being formed.
+Remote node allows autoconfiguration - size of the storage and
+checksumming will be requested during node initialization (if remote
+node supports checksumming it will be turned on).
+
+
+Each node or set of them can be formed into single array, which
+in turn becomes a local node, which can be exported further by stacking
+a local export node on top of it.
+
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+One can find more details in Documentation/dst/algorithms.txt file.
+
+Main goal of the distributed storage is to combine remote nodes into
+single device, so each block IO request is being sent over the network
+(contrary requests for local nodes are handled by the gneric block
+layer features). Each network connection has number of variables which
+describe it (socket, list of requests, error handling and so on),
+which form kst_state structure. This network state is added into per-socket
+polling state machine, and can be processed by dedicated thread when
+becomes ready. This system forms asynchronous IO for given block
+requests. If block request can be processed without blocking, then
+no new structures are allocated and async part of the state is not used.
+
+When connection to the remote peer breaks, DST core tries to reconnect
+to failed node and no requests are marked as errorneous, instead
+they live in the queue until reconnectin is established.
+
+Userspace code, setup documentation and examples can be found on project's
+homepage above.
diff --git a/Documentation/dst/sysfs.txt b/Documentation/dst/sysfs.txt
new file mode 100644
index 0000000..79d79dc
--- /dev/null
+++ b/Documentation/dst/sysfs.txt
@@ -0,0 +1,30 @@
+This file describes sysfs files created for each storage.
+
+1. Per-storage files.
+Each storage has its own dir /sysfs/devices/$storage_name,
+which contains following files:
+
+alg - contains name of the algorithm used to created given storage
+name - name of the storage
+nodes - map of the storage (list of nodes and their sizes and starts)
+remove_all_nodes - writable file which allows to remove all nodes from given
+	storage
+n-$start-$cookie - per node directory, where
+	$start - start of the given node in sectors,
+	$cookie - unique node's id used by DST
+
+2. Per-node files.
+Node's files are located in /sysfs/devices/$storage_name/n-$start-$cookie
+directory, described above.
+
+chunks - private file for mirroring algorithm, contains map of update/dirty
+	sectors of the node, '-' means update, '+' is dirty and has to be
+	resynced sector
+clean - writable file, writing leads to marking node as clean (in sync)
+dirty - writable file, writing leads to marking node as dirty (not in sync)
+size - size of the given node in sectors
+start - start of the given node in the storage in sectors
+type - contains type of the node in the following format: $type: $dev
+	where $type is either 'L' or 'R' - local or remote acordingly,
+	and $dev is device name for local node (/dev/sda1 for example)
+	or address of the remote node (192.168.4.81:1025 for example)

Re: [1/4] DST: Distributed storage documentation.

[Kay Sievers]

On Dec 10, 2007 12:47 PM, Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote:
> diff --git a/Documentation/dst/sysfs.txt b/Documentation/dst/sysfs.txt
> new file mode 100644
> index 0000000..79d79dc
> --- /dev/null
> +++ b/Documentation/dst/sysfs.txt
> @@ -0,0 +1,30 @@
> +This file describes sysfs files created for each storage.
> +
> +1. Per-storage files.
> +Each storage has its own dir /sysfs/devices/$storage_name,

It's always /sys/devices/.

> +which contains following files:
> +
> +alg - contains name of the algorithm used to created given storage
> +name - name of the storage
> +nodes - map of the storage (list of nodes and their sizes and starts)
> +remove_all_nodes - writable file which allows to remove all nodes from given
> +       storage
> +n-$start-$cookie - per node directory, where
> +       $start - start of the given node in sectors,
> +       $cookie - unique node's id used by DST
> +
> +2. Per-node files.
> +Node's files are located in /sysfs/devices/$storage_name/n-$start-$cookie
> +directory, described above.

To which class or bus do the devices you create belong? Care to show a
"tree" or "ls -la" of the device?

Kay

Re: [1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

On Mon, Dec 10, 2007 at 01:51:43PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> On Dec 10, 2007 12:47 PM, Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote:
> > diff --git a/Documentation/dst/sysfs.txt b/Documentation/dst/sysfs.txt
> > new file mode 100644
> > index 0000000..79d79dc
> > --- /dev/null
> > +++ b/Documentation/dst/sysfs.txt
> > @@ -0,0 +1,30 @@
> > +This file describes sysfs files created for each storage.
> > +
> > +1. Per-storage files.
> > +Each storage has its own dir /sysfs/devices/$storage_name,
> 
> It's always /sys/devices/.

I meant that for each new device, it will be placed into
/sys/devices/its_name, but it can also be accessed via
/sys/bus/dst/devices/

> > +which contains following files:
> > +
> > +alg - contains name of the algorithm used to created given storage
> > +name - name of the storage
> > +nodes - map of the storage (list of nodes and their sizes and starts)
> > +remove_all_nodes - writable file which allows to remove all nodes from given
> > +       storage
> > +n-$start-$cookie - per node directory, where
> > +       $start - start of the given node in sectors,
> > +       $cookie - unique node's id used by DST
> > +
> > +2. Per-node files.
> > +Node's files are located in /sysfs/devices/$storage_name/n-$start-$cookie
> > +directory, described above.
> 
> To which class or bus do the devices you create belong? Care to show a
> "tree" or "ls -la" of the device?

It is 'dst' bus.

uganda:~/codes# ls -la /sys/devices/staorge/
total 0
drwxr-xr-x 4 root root    0 2007-12-10 11:46 .
drwxr-xr-x 9 root root    0 2007-12-10 11:46 ..
-r--r--r-- 1 root root 4096 2007-12-10 11:46 alg
lrwxrwxrwx 1 root root    0 2007-12-10 11:46 bus -> ../../bus/dst
drwxr-xr-x 3 root root    0 2007-12-10 11:46 n-0-ffff81003e24117
-r--r--r-- 1 root root 4096 2007-12-10 11:46 name
-r--r--r-- 1 root root 4096 2007-12-10 11:46 nodes
drwxr-xr-x 2 root root    0 2007-12-10 11:46 power
-rw-r--r-- 1 root root 4096 2007-12-10 11:46 remove_all_nodes
lrwxrwxrwx 1 root root    0 2007-12-10 11:46 subsystem -> ../../bus/dst
-rw-r--r-- 1 root root 4096 2007-12-10 11:46 uevent
uganda:~/codes# ls -l /sys/bus/dst/
total 0
drwxr-xr-x 2 root root    0 2007-12-10 09:52 devices
drwxr-xr-x 2 root root    0 2007-12-10 09:52 drivers
-rw-r--r-- 1 root root 4096 2007-12-10 11:46 drivers_autoprobe
--w------- 1 root root 4096 2007-12-10 11:46 drivers_probe


> Kay

-- 
	Evgeniy Polyakov

Re: [1/4] DST: Distributed storage documentation.

[Kay Sievers]

On Mon, 2007-12-10 at 15:58 +0300, Evgeniy Polyakov wrote:
> On Mon, Dec 10, 2007 at 01:51:43PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> > On Dec 10, 2007 12:47 PM, Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote:
> > > diff --git a/Documentation/dst/sysfs.txt b/Documentation/dst/sysfs.txt
> > > new file mode 100644
> > > index 0000000..79d79dc
> > > --- /dev/null
> > > +++ b/Documentation/dst/sysfs.txt
> > > @@ -0,0 +1,30 @@
> > > +This file describes sysfs files created for each storage.
> > > +
> > > +1. Per-storage files.
> > > +Each storage has its own dir /sysfs/devices/$storage_name,
> > 
> > It's always /sys/devices/.
> 
> I meant that for each new device, it will be placed into
> /sys/devices/its_name, but it can also be accessed via
> /sys/bus/dst/devices/

Still, it looks like a path. :)

Please don't reference any device directly with a /sys/devices/ path.
You have to use the subsystem links to the devices
in /sys/bus/dst/devices/. Devices are free to move around
in /sys/devices, even during runtime. Yours don't do, but anyway, please
remove all mentioning of direct access to /sys/devices/.

Btw, where is the top-level /sys/devices/storage/ coming from? I don't
see that in the code. We don't accept any new "virtual parents" here.
Your devices will automatically appear in /sys/devices/virtual/dst/, and
not below your own parent. But that path does not matter anyway, because
you should only access them from the /sys/bus/dst/devices/ directory.

And in general please don't claim generic names like "storage" in any
namespace for a very specific subsystem like this.

> > > +which contains following files:
> > > +
> > > +alg - contains name of the algorithm used to created given storage
> > > +name - name of the storage
> > > +nodes - map of the storage (list of nodes and their sizes and starts)
> > > +remove_all_nodes - writable file which allows to remove all nodes from given
> > > +       storage
> > > +n-$start-$cookie - per node directory, where
> > > +       $start - start of the given node in sectors,
> > > +       $cookie - unique node's id used by DST
> > > +
> > > +2. Per-node files.
> > > +Node's files are located in /sysfs/devices/$storage_name/n-$start-$cookie
> > > +directory, described above.
> > 
> > To which class or bus do the devices you create belong? Care to show a
> > "tree" or "ls -la" of the device?
> 
> It is 'dst' bus.
> 
> uganda:~/codes# ls -la /sys/devices/staorge/
> total 0
> drwxr-xr-x 4 root root    0 2007-12-10 11:46 .
> drwxr-xr-x 9 root root    0 2007-12-10 11:46 ..
> -r--r--r-- 1 root root 4096 2007-12-10 11:46 alg
> lrwxrwxrwx 1 root root    0 2007-12-10 11:46 bus -> ../../bus/dst
> drwxr-xr-x 3 root root    0 2007-12-10 11:46 n-0-ffff81003e24117
> -r--r--r-- 1 root root 4096 2007-12-10 11:46 name
> -r--r--r-- 1 root root 4096 2007-12-10 11:46 nodes
> drwxr-xr-x 2 root root    0 2007-12-10 11:46 power
> -rw-r--r-- 1 root root 4096 2007-12-10 11:46 remove_all_nodes
> lrwxrwxrwx 1 root root    0 2007-12-10 11:46 subsystem -> ../../bus/dst
> -rw-r--r-- 1 root root 4096 2007-12-10 11:46 uevent

Ok, how does:
  ls -l /sys/devices/storage/n-0-ffff81003e24117
look?

> uganda:~/codes# ls -l /sys/bus/dst/
> total 0
> drwxr-xr-x 2 root root    0 2007-12-10 09:52 devices
> drwxr-xr-x 2 root root    0 2007-12-10 09:52 drivers
> -rw-r--r-- 1 root root 4096 2007-12-10 11:46 drivers_autoprobe
> --w------- 1 root root 4096 2007-12-10 11:46 drivers_probe

How does:
  ls -l /sys/bus/dst/devices
look?


Further questions:
Why do you do your own refcounting instead of using kref?
Why don't you use groups for the attributes?
Why don't you use default attributes for the device, where you get all
error handling done by the core.

Kay

Re: [1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

On Mon, Dec 10, 2007 at 03:31:48PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> > I meant that for each new device, it will be placed into
> > /sys/devices/its_name, but it can also be accessed via
> > /sys/bus/dst/devices/
> 
> Still, it looks like a path. :)
> 
> Please don't reference any device directly with a /sys/devices/ path.
> You have to use the subsystem links to the devices
> in /sys/bus/dst/devices/. Devices are free to move around
> in /sys/devices, even during runtime. Yours don't do, but anyway, please
> remove all mentioning of direct access to /sys/devices/.

Ok, I will update documentation to reference /sys/bus/dst/devices
instead of /sys/devices

> Btw, where is the top-level /sys/devices/storage/ coming from? I don't
> see that in the code. We don't accept any new "virtual parents" here.
>
> Your devices will automatically appear in /sys/devices/virtual/dst/, and
> not below your own parent. But that path does not matter anyway, because
> you should only access them from the /sys/bus/dst/devices/ directory.
> 
> And in general please don't claim generic names like "storage" in any
> namespace for a very specific subsystem like this.

It is not a parent - it is an example for device called 'storage', if it
will be called 'testing', then path will be /sys/devices/testing or more
correct /sys/bus/dst/devices/testing :)

> > It is 'dst' bus.
> > 
> > uganda:~/codes# ls -la /sys/devices/staorge/
> > total 0
> > drwxr-xr-x 4 root root    0 2007-12-10 11:46 .
> > drwxr-xr-x 9 root root    0 2007-12-10 11:46 ..
> > -r--r--r-- 1 root root 4096 2007-12-10 11:46 alg
> > lrwxrwxrwx 1 root root    0 2007-12-10 11:46 bus -> ../../bus/dst
> > drwxr-xr-x 3 root root    0 2007-12-10 11:46 n-0-ffff81003e24117
> > -r--r--r-- 1 root root 4096 2007-12-10 11:46 name
> > -r--r--r-- 1 root root 4096 2007-12-10 11:46 nodes
> > drwxr-xr-x 2 root root    0 2007-12-10 11:46 power
> > -rw-r--r-- 1 root root 4096 2007-12-10 11:46 remove_all_nodes
> > lrwxrwxrwx 1 root root    0 2007-12-10 11:46 subsystem -> ../../bus/dst
> > -rw-r--r-- 1 root root 4096 2007-12-10 11:46 uevent
> 
> Ok, how does:
>   ls -l /sys/devices/storage/n-0-ffff81003e24117
> look?

uganda:~/codes# ls -l /sys/devices/storage/n-0-ffff81003ebc220/
total 0
drwxr-xr-x 2 root root    0 2007-12-10 13:23 power
-r--r--r-- 1 root root 4096 2007-12-10 13:30 size
-r--r--r-- 1 root root 4096 2007-12-10 13:30 start
-r--r--r-- 1 root root 4096 2007-12-10 13:30 type
-rw-r--r-- 1 root root 4096 2007-12-10 13:30 uevent


> > uganda:~/codes# ls -l /sys/bus/dst/
> > total 0
> > drwxr-xr-x 2 root root    0 2007-12-10 09:52 devices
> > drwxr-xr-x 2 root root    0 2007-12-10 09:52 drivers
> > -rw-r--r-- 1 root root 4096 2007-12-10 11:46 drivers_autoprobe
> > --w------- 1 root root 4096 2007-12-10 11:46 drivers_probe
> 
> How does:
>   ls -l /sys/bus/dst/devices
> look?

uganda:~/codes# ls -la /sys/bus/dst/devices/
total 0
drwxr-xr-x 2 root root 0 2007-12-10 13:30 .
drwxr-xr-x 4 root root 0 2007-12-10 13:22 ..
lrwxrwxrwx 1 root root 0 2007-12-10 13:30 storage -> ../../../devices/storage


Here 'storage' is just a name for device called 'storage', it can be
anything else.
 
> Further questions:
> Why do you do your own refcounting instead of using kref?

That's because I always used atomic operations as a reference counters
and did not tried krefs :)
They are the same actually (module tricky arches where smp_mb_* are
required), so I can replace them in the next release.

> Why don't you use groups for the attributes?

For 3-4 attributes it is faster to register them in a loop than typing
another structure :)

> Why don't you use default attributes for the device, where you get all
> error handling done by the core.

What is 'default attributes' and for what devices?
All my sysfs files are so much trivial, so they do not need anything
special and I do not see what is error handling you mentioned.

-- 
	Evgeniy Polyakov

Re: [1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

On Mon, Dec 10, 2007 at 05:50:55PM +0300, Evgeniy Polyakov (johnpol@2ka.mipt.ru) wrote:
> > Further questions:
> > Why do you do your own refcounting instead of using kref?
> 
> That's because I always used atomic operations as a reference counters
> and did not tried krefs :)
> They are the same actually (module tricky arches where smp_mb_* are
> required), so I can replace them in the next release.

Actually not - I have to set reference counter to something other than 1
or +/- 1, and thus will have to call kref_get() in a loop, which is a
very ugly step. Is there kref_set() or somethinglike that? At least not
in 2.6.22 what I'm using for now.

Sigh, I've converted most of the DST already...

-- 
	Evgeniy Polyakov

Re: [1/4] DST: Distributed storage documentation.

[Kay Sievers]

On Mon, 2007-12-10 at 17:50 +0300, Evgeniy Polyakov wrote:
> On Mon, Dec 10, 2007 at 03:31:48PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> > > I meant that for each new device, it will be placed into
> > > /sys/devices/its_name, but it can also be accessed via
> > > /sys/bus/dst/devices/
> > 
> > Still, it looks like a path. :)
> > 
> > Please don't reference any device directly with a /sys/devices/ path.
> > You have to use the subsystem links to the devices
> > in /sys/bus/dst/devices/. Devices are free to move around
> > in /sys/devices, even during runtime. Yours don't do, but anyway, please
> > remove all mentioning of direct access to /sys/devices/.
> 
> Ok, I will update documentation to reference /sys/bus/dst/devices
> instead of /sys/devices

Great, thanks!

> > Btw, where is the top-level /sys/devices/storage/ coming from? I don't
> > see that in the code. We don't accept any new "virtual parents" here.
> >
> > Your devices will automatically appear in /sys/devices/virtual/dst/, and
> > not below your own parent. But that path does not matter anyway, because
> > you should only access them from the /sys/bus/dst/devices/ directory.
> > 
> > And in general please don't claim generic names like "storage" in any
> > namespace for a very specific subsystem like this.
> 
> It is not a parent - it is an example for device called 'storage', if it
> will be called 'testing', then path will be /sys/devices/testing or more
> correct /sys/bus/dst/devices/testing :)

Ah, I see.

> > > It is 'dst' bus.
> > > 
> > > uganda:~/codes# ls -la /sys/devices/staorge/
> > > total 0
> > > drwxr-xr-x 4 root root    0 2007-12-10 11:46 .
> > > drwxr-xr-x 9 root root    0 2007-12-10 11:46 ..
> > > -r--r--r-- 1 root root 4096 2007-12-10 11:46 alg
> > > lrwxrwxrwx 1 root root    0 2007-12-10 11:46 bus -> ../../bus/dst
> > > drwxr-xr-x 3 root root    0 2007-12-10 11:46 n-0-ffff81003e24117
> > > -r--r--r-- 1 root root 4096 2007-12-10 11:46 name
> > > -r--r--r-- 1 root root 4096 2007-12-10 11:46 nodes
> > > drwxr-xr-x 2 root root    0 2007-12-10 11:46 power
> > > -rw-r--r-- 1 root root 4096 2007-12-10 11:46 remove_all_nodes
> > > lrwxrwxrwx 1 root root    0 2007-12-10 11:46 subsystem -> ../../bus/dst
> > > -rw-r--r-- 1 root root 4096 2007-12-10 11:46 uevent
> > 
> > Ok, how does:
> >   ls -l /sys/devices/storage/n-0-ffff81003e24117
> > look?
> 
> uganda:~/codes# ls -l /sys/devices/storage/n-0-ffff81003ebc220/
> total 0
> drwxr-xr-x 2 root root    0 2007-12-10 13:23 power
> -r--r--r-- 1 root root 4096 2007-12-10 13:30 size
> -r--r--r-- 1 root root 4096 2007-12-10 13:30 start
> -r--r--r-- 1 root root 4096 2007-12-10 13:30 type
> -rw-r--r-- 1 root root 4096 2007-12-10 13:30 uevent

This is a "struct device" instance without a subsystem (bus/class),
right? It will not send an uevent to userspace. Is that intended? Why
don't you add them all to the dst bus? 

> > > uganda:~/codes# ls -l /sys/bus/dst/
> > > total 0
> > > drwxr-xr-x 2 root root    0 2007-12-10 09:52 devices
> > > drwxr-xr-x 2 root root    0 2007-12-10 09:52 drivers
> > > -rw-r--r-- 1 root root 4096 2007-12-10 11:46 drivers_autoprobe
> > > --w------- 1 root root 4096 2007-12-10 11:46 drivers_probe
> > 
> > How does:
> >   ls -l /sys/bus/dst/devices
> > look?
> 
> uganda:~/codes# ls -la /sys/bus/dst/devices/
> total 0
> drwxr-xr-x 2 root root 0 2007-12-10 13:30 .
> drwxr-xr-x 4 root root 0 2007-12-10 13:22 ..
> lrwxrwxrwx 1 root root 0 2007-12-10 13:30 storage -> ../../../devices/storage
> 
> Here 'storage' is just a name for device called 'storage', it can be
> anything else.

Fine.

> > Further questions:
> > Why do you do your own refcounting instead of using kref?
> 
> That's because I always used atomic operations as a reference counters
> and did not tried krefs :)
> They are the same actually (module tricky arches where smp_mb_* are
> required), so I can replace them in the next release.

On Mon, 2007-12-10 at 18:12 +0300, Evgeniy Polyakov wrote:
> Actually not - I have to set reference counter to something other than 1
> or +/- 1, and thus will have to call kref_get() in a loop, which is a
> very ugly step. Is there kref_set() or somethinglike that? At least not
> in 2.6.22 what I'm using for now.

Yeah, a loop would look pretty ugly. How about just adding kref_set(),
if you need it.

> > Why don't you use groups for the attributes?
> 
> For 3-4 attributes it is faster to register them in a loop than typing
> another structure :)

Yeah, but if you would need to recover from an error when the creation
of a file fails, a group would do the proper "rollback".

> > Why don't you use default attributes for the device, where you get all
> > error handling done by the core.
> 
> What is 'default attributes' and for what devices?
> All my sysfs files are so much trivial, so they do not need anything
> special and I do not see what is error handling you mentioned.

If all devices of a subsystem (bus/class) are of the same type, you can
set a default array of attributes in the "struct bus/class" to be
created at every device. If you have multiple types of devices in the
same subsytem (bus/class) you can to assign a the "device_type", which
has the default attribute group.
That way the core will create the files before the event is sent out to
userspace, and the files can be access from the event itself. Not sure
if that is needed for dst.

Thanks,
Kay

Re: [1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

On Mon, Dec 10, 2007 at 08:02:28PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> > uganda:~/codes# ls -l /sys/devices/storage/n-0-ffff81003ebc220/
> > total 0
> > drwxr-xr-x 2 root root    0 2007-12-10 13:23 power
> > -r--r--r-- 1 root root 4096 2007-12-10 13:30 size
> > -r--r--r-- 1 root root 4096 2007-12-10 13:30 start
> > -r--r--r-- 1 root root 4096 2007-12-10 13:30 type
> > -rw-r--r-- 1 root root 4096 2007-12-10 13:30 uevent
> 
> This is a "struct device" instance without a subsystem (bus/class),
> right? It will not send an uevent to userspace. Is that intended? Why
> don't you add them all to the dst bus? 

I created dst bus for storage devices only, nodes are very different
objects, and actually they do not need any events from above, but I need
to put some attributes somewhere, so it is 'empty' device.

> > Actually not - I have to set reference counter to something other than 1
> > or +/- 1, and thus will have to call kref_get() in a loop, which is a
> > very ugly step. Is there kref_set() or somethinglike that? At least not
> > in 2.6.22 what I'm using for now.
> 
> Yeah, a loop would look pretty ugly. How about just adding kref_set(),
> if you need it.

Well, then it distributed storage will not be able to build as
standalone module, and kref_set() itself will not be accepted as a single 
patch, since there are no in-kernel users :)
It is easily doable though.

> > > Why don't you use groups for the attributes?
> > 
> > For 3-4 attributes it is faster to register them in a loop than typing
> > another structure :)
> 
> Yeah, but if you would need to recover from an error when the creation
> of a file fails, a group would do the proper "rollback".

I do not care about such errors - if there is such an error for a file,
which exports information about type of the node (i.e. string "L" or "R")
or some other very meaningful info, then system has enough to care about
instead of this, so dst does not do anything special - it ignores such
errors :)

On exit path it will be checked and removed correctly.
If there will be additional sysfs files, I think group is a good way to
implement them.

> > > Why don't you use default attributes for the device, where you get all
> > > error handling done by the core.
> > 
> > What is 'default attributes' and for what devices?
> > All my sysfs files are so much trivial, so they do not need anything
> > special and I do not see what is error handling you mentioned.
> 
> If all devices of a subsystem (bus/class) are of the same type, you can
> set a default array of attributes in the "struct bus/class" to be
> created at every device. If you have multiple types of devices in the
> same subsytem (bus/class) you can to assign a the "device_type", which
> has the default attribute group.
> That way the core will create the files before the event is sent out to
> userspace, and the files can be access from the event itself. Not sure
> if that is needed for dst.

Ok, I see.

DST right now has 3 types of files - storage files, it is common for
every storage device; node files, which are the same for every node; and
per-algorithm private devices - they can be different (actually only
mirroring algorithm exports something to userspace).

I think it is possible to use default attributes for storage devices,
but node device does not have a bus/class, so they will be untouched.

> Thanks,
> Kay

-- 
	Evgeniy Polyakov

Re: [1/4] DST: Distributed storage documentation.

[Kay Sievers]

On Mon, 2007-12-10 at 22:33 +0300, Evgeniy Polyakov wrote:
> On Mon, Dec 10, 2007 at 08:02:28PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> > > uganda:~/codes# ls -l /sys/devices/storage/n-0-ffff81003ebc220/
> > > total 0
> > > drwxr-xr-x 2 root root    0 2007-12-10 13:23 power
> > > -r--r--r-- 1 root root 4096 2007-12-10 13:30 size
> > > -r--r--r-- 1 root root 4096 2007-12-10 13:30 start
> > > -r--r--r-- 1 root root 4096 2007-12-10 13:30 type
> > > -rw-r--r-- 1 root root 4096 2007-12-10 13:30 uevent
> > 
> > This is a "struct device" instance without a subsystem (bus/class),
> > right? It will not send an uevent to userspace. Is that intended? Why
> > don't you add them all to the dst bus? 
> 
> I created dst bus for storage devices only, nodes are very different
> objects, and actually they do not need any events from above, but I need
> to put some attributes somewhere, so it is 'empty' device.

Ok.

> > > Actually not - I have to set reference counter to something other than 1
> > > or +/- 1, and thus will have to call kref_get() in a loop, which is a
> > > very ugly step. Is there kref_set() or somethinglike that? At least not
> > > in 2.6.22 what I'm using for now.
> > 
> > Yeah, a loop would look pretty ugly. How about just adding kref_set(),
> > if you need it.
> 
> Well, then it distributed storage will not be able to build as
> standalone module, and kref_set() itself will not be accepted as a single 
> patch, since there are no in-kernel users :)
> It is easily doable though.

Most rules have exceptions. :) Send a patch, so we can see how it looks
like.

> > > > Why don't you use groups for the attributes?
> > > 
> > > For 3-4 attributes it is faster to register them in a loop than typing
> > > another structure :)
> > 
> > Yeah, but if you would need to recover from an error when the creation
> > of a file fails, a group would do the proper "rollback".
> 
> I do not care about such errors - if there is such an error for a file,
> which exports information about type of the node (i.e. string "L" or "R")
> or some other very meaningful info, then system has enough to care about
> instead of this, so dst does not do anything special - it ignores such
> errors :)
> 
> On exit path it will be checked and removed correctly.
> If there will be additional sysfs files, I think group is a good way to
> implement them.
> 
> > > > Why don't you use default attributes for the device, where you get all
> > > > error handling done by the core.
> > > 
> > > What is 'default attributes' and for what devices?
> > > All my sysfs files are so much trivial, so they do not need anything
> > > special and I do not see what is error handling you mentioned.
> > 
> > If all devices of a subsystem (bus/class) are of the same type, you can
> > set a default array of attributes in the "struct bus/class" to be
> > created at every device. If you have multiple types of devices in the
> > same subsytem (bus/class) you can to assign a the "device_type", which
> > has the default attribute group.
> > That way the core will create the files before the event is sent out to
> > userspace, and the files can be access from the event itself. Not sure
> > if that is needed for dst.
> 
> Ok, I see.
> 
> DST right now has 3 types of files - storage files, it is common for
> every storage device; node files, which are the same for every node; and
> per-algorithm private devices - they can be different (actually only
> mirroring algorithm exports something to userspace).
> 
> I think it is possible to use default attributes for storage devices,
> but node device does not have a bus/class, so they will be untouched.

Sounds fine.

Thanks,
Kay

Re: [1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

On Mon, Dec 10, 2007 at 08:44:55PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> > > > Actually not - I have to set reference counter to something other than 1
> > > > or +/- 1, and thus will have to call kref_get() in a loop, which is a
> > > > very ugly step. Is there kref_set() or somethinglike that? At least not
> > > > in 2.6.22 what I'm using for now.
> > > 
> > > Yeah, a loop would look pretty ugly. How about just adding kref_set(),
> > > if you need it.
> > 
> > Well, then it distributed storage will not be able to build as
> > standalone module, and kref_set() itself will not be accepted as a single 
> > patch, since there are no in-kernel users :)
> > It is easily doable though.
> 
> Most rules have exceptions. :) Send a patch, so we can see how it looks
> like.

It looks really non-trivial :)

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>

diff --git a/include/linux/kref.h b/include/linux/kref.h
index 6fee353..5d18563 100644
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -24,6 +24,7 @@ struct kref {
 	atomic_t refcount;
 };
 
+void kref_set(struct kref *kref, int num);
 void kref_init(struct kref *kref);
 void kref_get(struct kref *kref);
 int kref_put(struct kref *kref, void (*release) (struct kref *kref));
diff --git a/lib/kref.c b/lib/kref.c
index a6dc3ec..40aa9f9 100644
--- a/lib/kref.c
+++ b/lib/kref.c
@@ -15,13 +15,23 @@
 #include <linux/module.h>
 
 /**
+ * kref_set - initialize object and set refcount to requested number.
+ * @kref: object in question.
+ * @num: initial reference counter
+ */
+void kref_set(struct kref *kref, int num)
+{
+	atomic_set(&kref->refcount, num);
+	smp_mb();
+}
+
+/**
  * kref_init - initialize object.
  * @kref: object in question.
  */
 void kref_init(struct kref *kref)
 {
-	atomic_set(&kref->refcount,1);
-	smp_mb();
+	kref_set(kref, 1);
 }
 
 /**

-- 
	Evgeniy Polyakov

Re: [1/4] DST: Distributed storage documentation.

[Kay Sievers]

On Mon, 2007-12-10 at 22:51 +0300, Evgeniy Polyakov wrote:
> On Mon, Dec 10, 2007 at 08:44:55PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> > > > > Actually not - I have to set reference counter to something other than 1
> > > > > or +/- 1, and thus will have to call kref_get() in a loop, which is a
> > > > > very ugly step. Is there kref_set() or somethinglike that? At least not
> > > > > in 2.6.22 what I'm using for now.
> > > > 
> > > > Yeah, a loop would look pretty ugly. How about just adding kref_set(),
> > > > if you need it.
> > > 
> > > Well, then it distributed storage will not be able to build as
> > > standalone module, and kref_set() itself will not be accepted as a single 
> > > patch, since there are no in-kernel users :)
> > > It is easily doable though.
> > 
> > Most rules have exceptions. :) Send a patch, so we can see how it looks
> > like.
> 
> It looks really non-trivial :)

Yeah, it does. :)
We miss an EXPORT_SYMBOL(), right?

Kay

Re: [1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

On Mon, Dec 10, 2007 at 08:56:49PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> On Mon, 2007-12-10 at 22:51 +0300, Evgeniy Polyakov wrote:
> > On Mon, Dec 10, 2007 at 08:44:55PM +0100, Kay Sievers (kay.sievers@vrfy.org) wrote:
> > > > > > Actually not - I have to set reference counter to something other than 1
> > > > > > or +/- 1, and thus will have to call kref_get() in a loop, which is a
> > > > > > very ugly step. Is there kref_set() or somethinglike that? At least not
> > > > > > in 2.6.22 what I'm using for now.
> > > > > 
> > > > > Yeah, a loop would look pretty ugly. How about just adding kref_set(),
> > > > > if you need it.
> > > > 
> > > > Well, then it distributed storage will not be able to build as
> > > > standalone module, and kref_set() itself will not be accepted as a single 
> > > > patch, since there are no in-kernel users :)
> > > > It is easily doable though.
> > > 
> > > Most rules have exceptions. :) Send a patch, so we can see how it looks
> > > like.
> > 
> > It looks really non-trivial :)
> 
> Yeah, it does. :)
> We miss an EXPORT_SYMBOL(), right?

Yep :)

diff --git a/include/linux/kref.h b/include/linux/kref.h
index 6fee353..5d18563 100644
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -24,6 +24,7 @@ struct kref {
 	atomic_t refcount;
 };
 
+void kref_set(struct kref *kref, int num);
 void kref_init(struct kref *kref);
 void kref_get(struct kref *kref);
 int kref_put(struct kref *kref, void (*release) (struct kref *kref));
diff --git a/lib/kref.c b/lib/kref.c
index a6dc3ec..9ecd6e8 100644
--- a/lib/kref.c
+++ b/lib/kref.c
@@ -15,13 +15,23 @@
 #include <linux/module.h>
 
 /**
+ * kref_set - initialize object and set refcount to requested number.
+ * @kref: object in question.
+ * @num: initial reference counter
+ */
+void kref_set(struct kref *kref, int num)
+{
+	atomic_set(&kref->refcount, num);
+	smp_mb();
+}
+
+/**
  * kref_init - initialize object.
  * @kref: object in question.
  */
 void kref_init(struct kref *kref)
 {
-	atomic_set(&kref->refcount,1);
-	smp_mb();
+	kref_set(kref, 1);
 }
 
 /**
@@ -61,6 +71,7 @@ int kref_put(struct kref *kref, void (*release)(struct kref *kref))
 	return 0;
 }
 
+EXPORT_SYMBOL(kref_set);
 EXPORT_SYMBOL(kref_init);
 EXPORT_SYMBOL(kref_get);
 EXPORT_SYMBOL(kref_put);

-- 
	Evgeniy Polyakov

[0/4] DST: Distributed storage.

[Evgeniy Polyakov]

Distributed storage.

I'm pleased to announce the 10'th release of the distributed
storage subsystem (DST). This is a maintenance release and includes
bug fixes and simple feature extensions only.

DST allows to form a storage on top of local and remote nodes
and combine them into linear or mirroring setup, which in
turn can be exported to remote nodes.

Short changelog:
 * fixed bug with XFS metadata update (it can provide slab pages to the
	DST, so it is not allowed to transfer them using ->sendpage())
 * fixed async error completion path
 * extended netlink communication channel to report errors back to userspace
 * DST name is now "The 10'th dynasty of smuggled slothes"
 * number of fixes for userspace DST target

Great thanks to Matthew Hodgson <matthew@mxtelecom.com> for debugging and
fixes for userspace DST target and preliminary netlink extension patches.

Overall list of features of the DST can be found on project's homepage:

http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst

Thank you.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>

[1/4] DST: Distributed storage documentation.

[Evgeniy Polyakov]

Distributed storage documentation.

Algorithms used in the system, userspace interfaces
(sysfs dirs and files), design and implementation details
are described here.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


diff --git a/Documentation/dst/algorithms.txt b/Documentation/dst/algorithms.txt
new file mode 100644
index 0000000..1437a6a
--- /dev/null
+++ b/Documentation/dst/algorithms.txt
@@ -0,0 +1,115 @@
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+
+Let's briefly describe how they work.
+
+Linear algorithm.
+Simple approach of concatenating storages into single device with
+increased size is used in this algorithm. Essentially new device
+has size equal to sum of sizes of underlying nodes and nodes are
+placed one after another.
+
+  /----- Node 1 ---\                         /------ Node 3 ----\
+start              end                     start               end
+ |==================|========================|==================|
+ |                start                     end                 |
+ |                  \------- Node 2 ---------/                  |
+ |                                                              |
+start                                                          end
+ \-------------------------- DST storage ----------------------/
+
+			        /\
+			        ||
+			        ||
+
+			   IO operations
+
+			    Figure 1. 
+     3 nodes combined into single storage using linear algorithm.
+
+Mirror algorithm.
+In this algorithms nodes are placed under each other, so when
+operation comes to the first one, it can be mirrored to all
+underlying nodes. In case of reading, actual data is obtained from
+the nearest node - algoritm keeps track of previous operation
+and knows where it was stopped, so that subsequent seek to the 
+start of the new request will take the shortest time.
+Writing is always mirrored to all underlying nodes.
+
+                  IO operations
+                       ||
+                       ||
+                       \/
+
+|---------------- DST storage -------------------|
+|      prev position                             |
+|-------|------------ Node 1 --------------------|
+|                              prev pos          |
+|-------------------- Node 2 -----|--------------|
+|prev pos                                        |
+|---|---------------- Node 3 --------------------|
+
+		Figure 2.
+   3 nodes combined into single storage using mirror algorithm.
+
+Each algorithm must implement number of callbacks,
+which must be registered during initialization time.
+
+struct dst_alg_ops
+{
+	int			(*add_node)(struct dst_node *n);
+	void			(*del_node)(struct dst_node *n);
+	int 			(*remap)(struct dst_request *req);
+	int			(*error)(struct kst_state *state, int err);
+	struct module 		*owner;
+};
+
+@add_node.
+This callback is invoked when new node is being added into the storage,
+but before node is actually added into the storage, so that it could
+be accessed from it. When it is called, all appropriate initialization
+of the underlying device is already completed (system has been connected
+to remote node or got a reference to the local block device). At this
+stage algorithm can add node into private map. 
+It must return zero on success or negative value otherwise.
+
+@del_node.
+This callback is invoked when node is being deleted from the storage,
+i.e. when its reference counter hits zero. It is called before
+any cleaning is performed.
+It must return zero on success or negative value otherwise.
+
+@remap.
+This callback is invoked each time new bio hits the storage.
+Request structure contains BIO itself, pointer to the node, which originally
+stores the whole region under given IO request, and various parameters
+used by storage core to process this block request.
+It must return zero on success or negative value otherwise. It is upto
+this method to call all cleaning if remapping failed, for example it must
+call kst_bio_endio() for given callback in case of error, which in turn
+will call bio_endio(). Note, that dst_request structure provided in this
+callback is allocated on stack, so if there is a need to use it outside
+of the given function, it must be cloned (it will happen automatically
+in state's push callback, but that copy will not be shared by any other
+user).
+
+@error.
+This callback is invoked for each error, which happend when processed
+requests for remote nodes or when talking to remote size
+of the local export node (state contains data related to data
+transfers over the network).
+If this function has fixed given error, it must return 0 or negative
+error value otherwise.
+
+@owner.
+This is module reference counter updated automatically by DST core.
+
+Algorithm must provide its name and above structure to the 
+dst_alloc_alg() function, which will return a reference to the newly
+created algorithm.
+To remove it, one needs to call dst_remove_alg() with given algorithm
+pointer.
diff --git a/Documentation/dst/dst.txt b/Documentation/dst/dst.txt
new file mode 100644
index 0000000..a6ea126
--- /dev/null
+++ b/Documentation/dst/dst.txt
@@ -0,0 +1,69 @@
+Distributed storage. Design and implementation.
+http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst
+
+	     Evgeniy Polyakov
+
+This document is intended to briefly describe design and
+implementation details of the distributed storage project,
+aimed to create ability to group physically and/or logically
+distributed storages into single device.
+
+Main operational unit in the storage is node. Node can represent
+either remote storage, connected to local machine, or local
+device, or storage exported to the outside of the system.
+Here goes small explaination of basic therms.
+
+Local node.
+This node is just a logical link between block device (with given
+major and minor numbers) and structure in the DST hierarchy,
+which represents number of sectors on the area, corresponding to given
+block device. it can be a disk, a device mapper node or stacked
+block device on top of another underlying DST nodes.
+
+Local export node.
+Essentially the same as local node, but it allows to access
+to its data via network. Remote clients can connect to given local 
+export node and read or write blocks according to its size.
+Blocks are then forwarded to underlying local node and processed
+there accordingly to the nature of the local node.
+
+Remote node.
+This type of nodes contain remotely accessible devices. One can think
+about remote nodes as remote disks, which can be connected to
+local system and combined into single storage. Remote nodes
+are presented as number of sectors accessed over the network
+by the local machine, where distributed storage is being formed.
+Remote node allows autoconfiguration - size of the storage and
+checksumming will be requested during node initialization (if remote
+node supports checksumming it will be turned on).
+
+
+Each node or set of them can be formed into single array, which
+in turn becomes a local node, which can be exported further by stacking
+a local export node on top of it.
+
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+One can find more details in Documentation/dst/algorithms.txt file.
+
+Main goal of the distributed storage is to combine remote nodes into
+single device, so each block IO request is being sent over the network
+(contrary requests for local nodes are handled by the gneric block
+layer features). Each network connection has number of variables which
+describe it (socket, list of requests, error handling and so on),
+which form kst_state structure. This network state is added into per-socket
+polling state machine, and can be processed by dedicated thread when
+becomes ready. This system forms asynchronous IO for given block
+requests. If block request can be processed without blocking, then
+no new structures are allocated and async part of the state is not used.
+
+When connection to the remote peer breaks, DST core tries to reconnect
+to failed node and no requests are marked as errorneous, instead
+they live in the queue until reconnectin is established.
+
+Userspace code, setup documentation and examples can be found on project's
+homepage above.
diff --git a/Documentation/dst/sysfs.txt b/Documentation/dst/sysfs.txt
new file mode 100644
index 0000000..79d79dc
--- /dev/null
+++ b/Documentation/dst/sysfs.txt
@@ -0,0 +1,30 @@
+This file describes sysfs files created for each storage.
+
+1. Per-storage files.
+Each storage has its own dir /sysfs/devices/$storage_name,
+which contains following files:
+
+alg - contains name of the algorithm used to created given storage
+name - name of the storage
+nodes - map of the storage (list of nodes and their sizes and starts)
+remove_all_nodes - writable file which allows to remove all nodes from given
+	storage
+n-$start-$cookie - per node directory, where
+	$start - start of the given node in sectors,
+	$cookie - unique node's id used by DST
+
+2. Per-node files.
+Node's files are located in /sysfs/devices/$storage_name/n-$start-$cookie
+directory, described above.
+
+chunks - private file for mirroring algorithm, contains map of update/dirty
+	sectors of the node, '-' means update, '+' is dirty and has to be
+	resynced sector
+clean - writable file, writing leads to marking node as clean (in sync)
+dirty - writable file, writing leads to marking node as dirty (not in sync)
+size - size of the given node in sectors
+start - start of the given node in the storage in sectors
+type - contains type of the node in the following format: $type: $dev
+	where $type is either 'L' or 'R' - local or remote acordingly,
+	and $dev is device name for local node (/dev/sda1 for example)
+	or address of the remote node (192.168.4.81:1025 for example)

[0/4] dst: Distributed storage.

[Evgeniy Polyakov]

Distributed storage.

I'm pleased to announce the 9'th release of the distributed
storage subsystem (DST). This is maintenance release and include
bug fixing only.

DST allows to form a storage on top of local and remote nodes
and combine them into linear or mirroring setup, which in
turn can be exported to remote nodes.

Short changelog:
 * use node's size in sectors instead of bytes
 * fixed old/new ages for the first node. 
	Error spotted by Matthew Hodgson <matthew@mxtelecom.com>
 * fixed debug printk declaration
 * it is now called 'astonishingly screwed tapeworm'

Overall list of features of the DST can be found on project's homepage:

http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst

Thank you.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>

[1/4] dst: Distributed storage documentation.

[Evgeniy Polyakov]

Distributed storage documentation.

Algorithms used in the system, userspace interfaces
(sysfs dirs and files), design and implementation details
are described here.

Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


diff --git a/Documentation/dst/algorithms.txt b/Documentation/dst/algorithms.txt
new file mode 100644
index 0000000..1437a6a
--- /dev/null
+++ b/Documentation/dst/algorithms.txt
@@ -0,0 +1,115 @@
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+
+Let's briefly describe how they work.
+
+Linear algorithm.
+Simple approach of concatenating storages into single device with
+increased size is used in this algorithm. Essentially new device
+has size equal to sum of sizes of underlying nodes and nodes are
+placed one after another.
+
+  /----- Node 1 ---\                         /------ Node 3 ----\
+start              end                     start               end
+ |==================|========================|==================|
+ |                start                     end                 |
+ |                  \------- Node 2 ---------/                  |
+ |                                                              |
+start                                                          end
+ \-------------------------- DST storage ----------------------/
+
+			        /\
+			        ||
+			        ||
+
+			   IO operations
+
+			    Figure 1. 
+     3 nodes combined into single storage using linear algorithm.
+
+Mirror algorithm.
+In this algorithms nodes are placed under each other, so when
+operation comes to the first one, it can be mirrored to all
+underlying nodes. In case of reading, actual data is obtained from
+the nearest node - algoritm keeps track of previous operation
+and knows where it was stopped, so that subsequent seek to the 
+start of the new request will take the shortest time.
+Writing is always mirrored to all underlying nodes.
+
+                  IO operations
+                       ||
+                       ||
+                       \/
+
+|---------------- DST storage -------------------|
+|      prev position                             |
+|-------|------------ Node 1 --------------------|
+|                              prev pos          |
+|-------------------- Node 2 -----|--------------|
+|prev pos                                        |
+|---|---------------- Node 3 --------------------|
+
+		Figure 2.
+   3 nodes combined into single storage using mirror algorithm.
+
+Each algorithm must implement number of callbacks,
+which must be registered during initialization time.
+
+struct dst_alg_ops
+{
+	int			(*add_node)(struct dst_node *n);
+	void			(*del_node)(struct dst_node *n);
+	int 			(*remap)(struct dst_request *req);
+	int			(*error)(struct kst_state *state, int err);
+	struct module 		*owner;
+};
+
+@add_node.
+This callback is invoked when new node is being added into the storage,
+but before node is actually added into the storage, so that it could
+be accessed from it. When it is called, all appropriate initialization
+of the underlying device is already completed (system has been connected
+to remote node or got a reference to the local block device). At this
+stage algorithm can add node into private map. 
+It must return zero on success or negative value otherwise.
+
+@del_node.
+This callback is invoked when node is being deleted from the storage,
+i.e. when its reference counter hits zero. It is called before
+any cleaning is performed.
+It must return zero on success or negative value otherwise.
+
+@remap.
+This callback is invoked each time new bio hits the storage.
+Request structure contains BIO itself, pointer to the node, which originally
+stores the whole region under given IO request, and various parameters
+used by storage core to process this block request.
+It must return zero on success or negative value otherwise. It is upto
+this method to call all cleaning if remapping failed, for example it must
+call kst_bio_endio() for given callback in case of error, which in turn
+will call bio_endio(). Note, that dst_request structure provided in this
+callback is allocated on stack, so if there is a need to use it outside
+of the given function, it must be cloned (it will happen automatically
+in state's push callback, but that copy will not be shared by any other
+user).
+
+@error.
+This callback is invoked for each error, which happend when processed
+requests for remote nodes or when talking to remote size
+of the local export node (state contains data related to data
+transfers over the network).
+If this function has fixed given error, it must return 0 or negative
+error value otherwise.
+
+@owner.
+This is module reference counter updated automatically by DST core.
+
+Algorithm must provide its name and above structure to the 
+dst_alloc_alg() function, which will return a reference to the newly
+created algorithm.
+To remove it, one needs to call dst_remove_alg() with given algorithm
+pointer.
diff --git a/Documentation/dst/dst.txt b/Documentation/dst/dst.txt
new file mode 100644
index 0000000..a6ea126
--- /dev/null
+++ b/Documentation/dst/dst.txt
@@ -0,0 +1,69 @@
+Distributed storage. Design and implementation.
+http://tservice.net.ru/~s0mbre/old/?section=projects&item=dst
+
+	     Evgeniy Polyakov
+
+This document is intended to briefly describe design and
+implementation details of the distributed storage project,
+aimed to create ability to group physically and/or logically
+distributed storages into single device.
+
+Main operational unit in the storage is node. Node can represent
+either remote storage, connected to local machine, or local
+device, or storage exported to the outside of the system.
+Here goes small explaination of basic therms.
+
+Local node.
+This node is just a logical link between block device (with given
+major and minor numbers) and structure in the DST hierarchy,
+which represents number of sectors on the area, corresponding to given
+block device. it can be a disk, a device mapper node or stacked
+block device on top of another underlying DST nodes.
+
+Local export node.
+Essentially the same as local node, but it allows to access
+to its data via network. Remote clients can connect to given local 
+export node and read or write blocks according to its size.
+Blocks are then forwarded to underlying local node and processed
+there accordingly to the nature of the local node.
+
+Remote node.
+This type of nodes contain remotely accessible devices. One can think
+about remote nodes as remote disks, which can be connected to
+local system and combined into single storage. Remote nodes
+are presented as number of sectors accessed over the network
+by the local machine, where distributed storage is being formed.
+Remote node allows autoconfiguration - size of the storage and
+checksumming will be requested during node initialization (if remote
+node supports checksumming it will be turned on).
+
+
+Each node or set of them can be formed into single array, which
+in turn becomes a local node, which can be exported further by stacking
+a local export node on top of it.
+
+Each storage by itself is just a set of contiguous logical blocks, with
+allowed number of operations. Nodes, each of which has own start and size,
+are placed into storage by appropriate algorithm, which remaps
+logical sector number into real node's sector. One can create
+own algorithms, since DST has pluggable interface for that.
+Currently mirrored and linear algorithms are supported.
+One can find more details in Documentation/dst/algorithms.txt file.
+
+Main goal of the distributed storage is to combine remote nodes into
+single device, so each block IO request is being sent over the network
+(contrary requests for local nodes are handled by the gneric block
+layer features). Each network connection has number of variables which
+describe it (socket, list of requests, error handling and so on),
+which form kst_state structure. This network state is added into per-socket
+polling state machine, and can be processed by dedicated thread when
+becomes ready. This system forms asynchronous IO for given block
+requests. If block request can be processed without blocking, then
+no new structures are allocated and async part of the state is not used.
+
+When connection to the remote peer breaks, DST core tries to reconnect
+to failed node and no requests are marked as errorneous, instead
+they live in the queue until reconnectin is established.
+
+Userspace code, setup documentation and examples can be found on project's
+homepage above.
diff --git a/Documentation/dst/sysfs.txt b/Documentation/dst/sysfs.txt
new file mode 100644
index 0000000..79d79dc
--- /dev/null
+++ b/Documentation/dst/sysfs.txt
@@ -0,0 +1,30 @@
+This file describes sysfs files created for each storage.
+
+1. Per-storage files.
+Each storage has its own dir /sysfs/devices/$storage_name,
+which contains following files:
+
+alg - contains name of the algorithm used to created given storage
+name - name of the storage
+nodes - map of the storage (list of nodes and their sizes and starts)
+remove_all_nodes - writable file which allows to remove all nodes from given
+	storage
+n-$start-$cookie - per node directory, where
+	$start - start of the given node in sectors,
+	$cookie - unique node's id used by DST
+
+2. Per-node files.
+Node's files are located in /sysfs/devices/$storage_name/n-$start-$cookie
+directory, described above.
+
+chunks - private file for mirroring algorithm, contains map of update/dirty
+	sectors of the node, '-' means update, '+' is dirty and has to be
+	resynced sector
+clean - writable file, writing leads to marking node as clean (in sync)
+dirty - writable file, writing leads to marking node as dirty (not in sync)
+size - size of the given node in sectors
+start - start of the given node in the storage in sectors
+type - contains type of the node in the following format: $type: $dev
+	where $type is either 'L' or 'R' - local or remote acordingly,
+	and $dev is device name for local node (/dev/sda1 for example)
+	or address of the remote node (192.168.4.81:1025 for example)

Re: [1/4] dst: Distributed storage documentation.

[Matt Mackall]

On Thu, Nov 29, 2007 at 03:53:23PM +0300, Evgeniy Polyakov wrote:
> 
> Distributed storage documentation.
> 
> Algorithms used in the system, userspace interfaces
> (sysfs dirs and files), design and implementation details
> are described here.

Can you give us a summary of how this differs from using device mapper
with NBD?

-- 
Mathematics is the supreme nostalgia of our time.

Re: [1/4] dst: Distributed storage documentation.

[Evgeniy Polyakov]

Hi Matt.

On Sun, Dec 02, 2007 at 10:50:59PM -0600, Matt Mackall (mpm@selenic.com) wrote:
> > Distributed storage documentation.
> > 
> > Algorithms used in the system, userspace interfaces
> > (sysfs dirs and files), design and implementation details
> > are described here.
> 
> Can you give us a summary of how this differs from using device mapper
> with NBD?

>From the higher point ov view it does not, but it operates quite differently:
it has async processing of the requests, thus not blocking, it has
different protocol with smaller overhead, supports strong checksums, has
in-kernel export server, which supports simple security attributes (i.e.
allow to connect, to read or write). It uses smaller amount of memory
(zero additional allocations in the common path for linear mapping,
not including network allocations, it uses smaller amount of additional
allocations for mirroring case).
DST supports failure recovery in case of dropped connection (core will
reconnect to the remote node when it is ready), thus it is possible to
turn off and on remote nodes without special administration steps. DST
has simple autoconfiguration at the startup time (support checksums and
storage size autonegotiation). It is possible to turn one of the mirror
nodes off and use it as a offline backup, since dst mirror node stores
data at the end of the storage, so it can be mounted locally.

-- 
	Evgeniy Polyakov