[PATCH v7 0/3] ubi: Add block interface

[PATCH v7 0/3] ubi: Add block interface

[Ezequiel Garcia]

This patch adds read-only block device access on top of UBI volumes, allowing
for a ligthweigth solution to mount block-oriented filesystems on top of
flash devices.

The main target of this patch is supporting lighter, read-only filesystem,
by putting a squashfs on top of ubiblock.

You can read this discussion if you are want more historical details:

  http://lkml.indiana.edu/hypermail/linux/kernel/1211.2/02556.html

In particular, it's important to note this already has users:

  1. http://permalink.gmane.org/gmane.linux.drivers.mtd/46221

  2. http://permalink.gmane.org/gmane.linux.drivers.mtd/49385

  3. Myself

(Artem: I hope I've addressed all your feedback on v5.)

More feedback, comments and testing welcome/needed.

* Changes from v6

  * Changed the user-space tool name: ubiblock.

  * Amended the website documentation and all the comments in code to
    remove any reference to write support or the lack of a cache.

  * Changed the type of the requested byte address to 'loff_t', removing
    the limitation on the UBI volume size. Accordingly, use do_div()
    to get the leb:offset address.

  * Changed thea ubiblock structure mutex name: s/vol_mutex/dev_mutex.

  * Changed the ubiblock_init() error handling so it returns an error
    if it fails to attach any user-requested block. Accordingly, ubi_init()
    has been changed to error (thus UBI fails to load, if compiled as module)
    if ubiblock_init() fails.

* Changes from v5

  * Remove stupid comment about code aesthetic.

  * Rework comments inside the driver and added user documentation to the
    mtd website.

  * Included the mtd-utils patch, adding the ubiblkvol user-space tool.

* Changes from v4

  * Dropped write-support

  * Dropped cached access

* Changes from v3

  * Replaced the 2-LEB (read and write) for a 1-LEB cache. This was done
    to prevent any cache-coherency issues and to avoid over-design.
    It's not clear having a separate read and write cache has a dramatical
    impact on wear leveling or performance.

  * Made the 1-LEB cache optional. Based on a suggestion by Piergiorgio
    Beruto, caching at the block level would be redundant and ineffective.
    The filesystem has a better chance of caching.

    Some very simple tests on squashfs (ubiblock's primary target) showed
    that squashfs does a great job on caching its file accesses.

    Given a LEB can be quite big on some devices O(~100KiB), it can be
    interesting to remove the cache altogether on memory-constrained platforms.

  * Make UBI_IOCVOLDETBLK return an error if the detaching wasn't successful,
    as suggested by Mike Frysinger.

  * Fixed a bunch of typos and suggestions made by Mike Frysinger.

* Changes from v2

  * On this 3rd version of the patch I've re-worked the patch considerably,
    mostly integrating it with UBI, instead of making it a separate module.

    Despite this integration, the ubiblock code is still completely independent
    of the UBI core and it can be completely compiled-out through configuration.

  * Making ubiblock part of UBI allows to add ioctl access to attach/detach
    block devices to/from UBI volumes in a very simple way.

  * A new tool 'ubiblkvol' is added to ubi-utils to access these two new ioctls.

  * To address the 'write or not to write' discussion, the write support is
    enabled with a kernel option and there's a big fat 'DANGEROUS' label on it
    to prevent misusage.

Ezequiel Garcia (1):
  ubi: Introduce block devices for UBI volumes

 drivers/mtd/ubi/Kconfig     |  19 ++
 drivers/mtd/ubi/Makefile    |   1 +
 drivers/mtd/ubi/block.c     | 660 ++++++++++++++++++++++++++++++++++++++++++++
 drivers/mtd/ubi/build.c     |   5 +
 drivers/mtd/ubi/cdev.c      |  20 ++
 drivers/mtd/ubi/ubi.h       |  14 +
 include/uapi/mtd/ubi-user.h |  11 +
 7 files changed, 730 insertions(+)
 create mode 100644 drivers/mtd/ubi/block.c

--
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Brian Norris <computersforpeace@gmail.com>
Cc: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Piergiorgio Beruto <piergiorgio.beruto@gmail.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Richard Weinberger <richard.weinberger@gmail.com>

-- 
1.8.1.5

[PATCH v7 1/3] ubi: Introduce read-only block devices on top of UBI volumes

[Ezequiel Garcia]

This commit introduces read-only block device emulation on top of UBI volumes.

Given UBI takes care of wear leveling and bad block management it's possible
to add a thin layer to enable block device access to UBI volumes.
This allows to use a block-oriented filesystem on a flash device.

The UBI block devices are meant to be used in conjunction with any
regular, block-oriented file system (e.g. ext4), although it's primarily
targeted at read-only file systems, such as squashfs.

Block devices are created upon user request through new ioctls:
UBI_IOCVOLATTBLK to attach and UBI_IOCVOLDETBLK to detach.
Also, a new UBI module parameter is added 'ubi.block'. This parameter is
needed in order to attach a block device on boot-up time, allowing to
mount the rootfs on a ubiblock device.
For instance, you could have these kernel parameters:

  ubi.mtd=5 ubi.block=0,0 root=/dev/ubiblock0_0

Or, if you compile ubi as a module:

  $ modprobe ubi mtd=/dev/mtd5 block=/dev/ubi0_0

Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Brian Norris <computersforpeace@gmail.com>
Cc: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Piergiorgio Beruto <piergiorgio.beruto@gmail.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Richard Weinberger <richard.weinberger@gmail.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
---
 drivers/mtd/ubi/Kconfig     |  15 +
 drivers/mtd/ubi/Makefile    |   1 +
 drivers/mtd/ubi/block.c     | 668 ++++++++++++++++++++++++++++++++++++++++++++
 drivers/mtd/ubi/build.c     |  11 +
 drivers/mtd/ubi/cdev.c      |  20 ++
 drivers/mtd/ubi/ubi.h       |  14 +
 include/uapi/mtd/ubi-user.h |  11 +
 7 files changed, 740 insertions(+)
 create mode 100644 drivers/mtd/ubi/block.c

diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index 36663af..783fb18 100644
--- a/drivers/mtd/ubi/Kconfig
+++ b/drivers/mtd/ubi/Kconfig
@@ -87,4 +87,19 @@ config MTD_UBI_GLUEBI
 	   work on top of UBI. Do not enable this unless you use legacy
 	   software.
 
+config MTD_UBI_BLOCK
+	bool "Read-only block devices on top of UBI volumes"
+	default n
+	help
+	   This option enables read-only UBI block devices support. UBI block
+	   devices will be layered on top of UBI volumes, which means that the
+	   UBI driver will transparently handle things like bad eraseblocks and
+	   bit-flips. You can put any block-oriented file system on top of UBI
+	   volumes in read-only mode (e.g., ext4), but it is probably most
+	   practical for read-only file systems, like squashfs.
+
+	   When selected, this feature will be built in the UBI driver.
+
+	   If in doubt, say "N".
+
 endif # MTD_UBI
diff --git a/drivers/mtd/ubi/Makefile b/drivers/mtd/ubi/Makefile
index b46b0c97..4e3c3d7 100644
--- a/drivers/mtd/ubi/Makefile
+++ b/drivers/mtd/ubi/Makefile
@@ -3,5 +3,6 @@ obj-$(CONFIG_MTD_UBI) += ubi.o
 ubi-y += vtbl.o vmt.o upd.o build.o cdev.o kapi.o eba.o io.o wl.o attach.o
 ubi-y += misc.o debug.o
 ubi-$(CONFIG_MTD_UBI_FASTMAP) += fastmap.o
+ubi-$(CONFIG_MTD_UBI_BLOCK) += block.o
 
 obj-$(CONFIG_MTD_UBI_GLUEBI) += gluebi.o
diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
new file mode 100644
index 0000000..06dccce
--- /dev/null
+++ b/drivers/mtd/ubi/block.c
@@ -0,0 +1,668 @@
+/*
+ * Copyright (c) 2014 Ezequiel Garcia
+ * Copyright (c) 2011 Free Electrons
+ *
+ * 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, version 2.
+ *
+ * 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.
+ */
+
+/*
+ * Read-only block devices on top of UBI volumes
+ *
+ * A simple implementation to allow a block device to be layered on top of a
+ * UBI volume. The implementation is provided by creating a static 1-to-1
+ * mapping between the block device and the UBI volume.
+ *
+ * The addressed byte is obtained from the addressed block sector, which is
+ * mapped linearly into the corresponding LEB:
+ *
+ *   leb number = addressed byte / leb size
+ *
+ * This feature is compiled in the UBI core, and adds a new 'block' parameter
+ * to allow early block device attaching. Runtime  block attach/detach for UBI
+ * volumes is provided through two new UBI ioctls: UBI_IOCVOLATTBLK and
+ * UBI_IOCVOLDETBLK.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/mtd/ubi.h>
+#include <linux/workqueue.h>
+#include <linux/blkdev.h>
+#include <linux/hdreg.h>
+#include <asm/div64.h>
+
+#include "ubi-media.h"
+#include "ubi.h"
+
+/* Maximum number of supported devices */
+#define UBIBLOCK_MAX_DEVICES 32
+
+/* Maximum length of the 'block=' parameter */
+#define UBIBLOCK_PARAM_LEN 63
+
+/* Maximum number of comma-separated items in the 'block=' parameter */
+#define UBIBLOCK_PARAM_COUNT 2
+
+struct ubiblock_param {
+	int ubi_num;
+	int vol_id;
+	char name[UBIBLOCK_PARAM_LEN+1];
+};
+
+/* Numbers of elements set in the @ubiblock_param array */
+static int ubiblock_devs __initdata;
+
+/* MTD devices specification parameters */
+static struct ubiblock_param ubiblock_param[UBIBLOCK_MAX_DEVICES] __initdata;
+
+struct ubiblock {
+	struct ubi_volume_desc *desc;
+	struct ubi_volume_info *vi;
+	int ubi_num;
+	int vol_id;
+	int refcnt;
+	int leb_size;
+
+	struct gendisk *gd;
+	struct request_queue *rq;
+
+	struct workqueue_struct *wq;
+	struct work_struct work;
+
+	struct mutex dev_mutex;
+	spinlock_t queue_lock;
+	struct list_head list;
+};
+
+/* Linked list of all ubiblock instances */
+static LIST_HEAD(ubiblock_devices);
+static DEFINE_MUTEX(devices_mutex);
+static int ubiblock_major;
+
+static int __init ubiblock_set_param(const char *val,
+				     const struct kernel_param *kp)
+{
+	int i, ret;
+	size_t len;
+	struct ubiblock_param *param;
+	char buf[UBIBLOCK_PARAM_LEN];
+	char *pbuf = &buf[0];
+	char *tokens[UBIBLOCK_PARAM_COUNT];
+
+	if (!val)
+		return -EINVAL;
+
+	len = strnlen(val, UBIBLOCK_PARAM_LEN);
+	if (len == 0) {
+		ubi_warn("block: empty 'block=' parameter - ignored\n");
+		return 0;
+	}
+
+	if (len == UBIBLOCK_PARAM_LEN) {
+		ubi_err("block: parameter \"%s\" is too long, max. is %d\n",
+			val, UBIBLOCK_PARAM_LEN);
+		return -EINVAL;
+	}
+
+	strcpy(buf, val);
+
+	/* Get rid of the final newline */
+	if (buf[len - 1] == '\n')
+		buf[len - 1] = '\0';
+
+	for (i = 0; i < UBIBLOCK_PARAM_COUNT; i++)
+		tokens[i] = strsep(&pbuf, ",");
+
+	param = &ubiblock_param[ubiblock_devs];
+	if (tokens[1]) {
+		/* Two parameters: can be 'ubi, vol_id' or 'ubi, vol_name' */
+		ret = kstrtoint(tokens[0], 10, &param->ubi_num);
+		if (ret < 0)
+			return -EINVAL;
+
+		/* Second param can be a number or a name */
+		ret = kstrtoint(tokens[1], 10, &param->vol_id);
+		if (ret < 0) {
+			param->vol_id = -1;
+			strcpy(param->name, tokens[1]);
+		}
+
+	} else {
+		/* One parameter: must be device path */
+		strcpy(param->name, tokens[0]);
+		param->ubi_num = -1;
+		param->vol_id = -1;
+	}
+
+	ubiblock_devs++;
+
+	return 0;
+}
+
+static const struct kernel_param_ops ubiblock_param_ops = {
+	.set    = ubiblock_set_param,
+};
+module_param_cb(block, &ubiblock_param_ops, NULL, 0);
+MODULE_PARM_DESC(block, "Attach block devices to UBI volumes. Parameter format: block=<path|dev,num|dev,name>.\n"
+			"Multiple \"block\" parameters may be specified.\n"
+			"UBI volumes may be specified by their number, name, or path to the device node.\n"
+			"Examples\n"
+			"Using the UBI volume path:\n"
+			"ubi.block=/dev/ubi0_0\n"
+			"Using the UBI device, and the volume name:\n"
+			"ubi.block=0,rootfs\n"
+			"Using both UBI device number and UBI volume number:\n"
+			"ubi.block=0,0\n");
+
+static struct ubiblock *find_dev_nolock(int ubi_num, int vol_id)
+{
+	struct ubiblock *dev;
+
+	list_for_each_entry(dev, &ubiblock_devices, list)
+		if (dev->ubi_num == ubi_num && dev->vol_id == vol_id)
+			return dev;
+	return NULL;
+}
+
+static int ubiblock_read_to_buf(struct ubiblock *dev, char *buffer,
+				int leb, int offset, int len)
+{
+	int ret;
+
+	ret = ubi_read(dev->desc, leb, buffer, offset, len);
+	if (ret) {
+		ubi_err("%s ubi_read error %d",
+			dev->gd->disk_name, ret);
+		return ret;
+	}
+	return 0;
+}
+
+static int ubiblock_read(struct ubiblock *dev, char *buffer,
+			 sector_t sec, int len)
+{
+	int ret, leb, offset;
+	int bytes_left = len;
+	int to_read = len;
+	loff_t pos = sec << 9;
+
+	/* Get leb:offset address to read from */
+	offset = do_div(pos, dev->leb_size);
+	leb = pos;
+
+	while (bytes_left) {
+
+		/*
+		 * We can only read one leb at a time.
+		 * Therefore if the read length is larger than
+		 * one leb size, we split the operation.
+		 */
+		if (offset + to_read > dev->leb_size)
+			to_read = dev->leb_size - offset;
+
+		ret = ubiblock_read_to_buf(dev, buffer, leb, offset, to_read);
+		if (ret)
+			return ret;
+
+		buffer += to_read;
+		bytes_left -= to_read;
+		to_read = bytes_left;
+		leb++;
+		offset = 0;
+	}
+	return 0;
+}
+
+static int do_ubiblock_request(struct ubiblock *dev, struct request *req)
+{
+	int len, ret;
+	sector_t sec;
+
+	if (req->cmd_type != REQ_TYPE_FS)
+		return -EIO;
+
+	if (blk_rq_pos(req) + blk_rq_cur_sectors(req) >
+	    get_capacity(req->rq_disk))
+		return -EIO;
+
+	if (rq_data_dir(req) != READ)
+		return -ENOSYS; /* Write not implemented */
+
+	sec = blk_rq_pos(req);
+	len = blk_rq_cur_bytes(req);
+
+	/*
+	 * Let's prevent the device from being removed while we're doing I/O
+	 * work. Notice that this means we serialize all the I/O operations,
+	 * but it's probably of no impact given the NAND core serializes
+	 * flash acceses anywafy.
+	 */
+	mutex_lock(&dev->dev_mutex);
+	ret = ubiblock_read(dev, req->buffer, sec, len);
+	mutex_unlock(&dev->dev_mutex);
+
+	return ret;
+}
+
+static void ubiblock_do_work(struct work_struct *work)
+{
+	struct ubiblock *dev =
+		container_of(work, struct ubiblock, work);
+	struct request_queue *rq = dev->rq;
+	struct request *req;
+	int res;
+
+	spin_lock_irq(rq->queue_lock);
+
+	req = blk_fetch_request(rq);
+	while (req) {
+
+		spin_unlock_irq(rq->queue_lock);
+		res = do_ubiblock_request(dev, req);
+		spin_lock_irq(rq->queue_lock);
+
+		/*
+		 * If we're done with this request,
+		 * we need to fetch a new one
+		 */
+		if (!__blk_end_request_cur(req, res))
+			req = blk_fetch_request(rq);
+	}
+
+	spin_unlock_irq(rq->queue_lock);
+}
+
+static void ubiblock_request(struct request_queue *rq)
+{
+	struct ubiblock *dev;
+	struct request *req;
+
+	dev = rq->queuedata;
+
+	if (!dev)
+		while ((req = blk_fetch_request(rq)) != NULL)
+			__blk_end_request_all(req, -ENODEV);
+	else
+		queue_work(dev->wq, &dev->work);
+}
+
+static int ubiblock_open(struct block_device *bdev, fmode_t mode)
+{
+	struct ubiblock *dev = bdev->bd_disk->private_data;
+	int ret;
+
+	mutex_lock(&dev->dev_mutex);
+	if (dev->refcnt > 0) {
+		/*
+		 * The volume is already open, just increase the reference
+		 * counter.
+		 */
+		goto out_done;
+	}
+
+	/*
+	 * We want users to be aware they should only mount us as read-only.
+	 * It's just a paranoid check, as write requests will get rejected
+	 * in any case.
+	 */
+	if (mode & FMODE_WRITE) {
+		ret = -EPERM;
+		goto out_unlock;
+	}
+
+	dev->desc = ubi_open_volume(dev->ubi_num, dev->vol_id, UBI_READONLY);
+	if (IS_ERR(dev->desc)) {
+		ubi_err("%s failed to open ubi volume %d_%d",
+			dev->gd->disk_name, dev->ubi_num, dev->vol_id);
+		ret = PTR_ERR(dev->desc);
+		dev->desc = NULL;
+		goto out_unlock;
+	}
+
+	dev->vi = kzalloc(sizeof(struct ubi_volume_info), GFP_KERNEL);
+	if (!dev->vi) {
+		ret = -ENOMEM;
+		goto out_close;
+	}
+
+out_done:
+	dev->refcnt++;
+	mutex_unlock(&dev->dev_mutex);
+	return 0;
+
+out_close:
+	ubi_close_volume(dev->desc);
+	dev->desc = NULL;
+out_unlock:
+	mutex_unlock(&dev->dev_mutex);
+	return ret;
+}
+
+static void ubiblock_release(struct gendisk *gd, fmode_t mode)
+{
+	struct ubiblock *dev = gd->private_data;
+
+	mutex_lock(&dev->dev_mutex);
+
+	dev->refcnt--;
+	if (dev->refcnt == 0) {
+		kfree(dev->vi);
+		ubi_close_volume(dev->desc);
+
+		dev->vi = NULL;
+		dev->desc = NULL;
+	}
+
+	mutex_unlock(&dev->dev_mutex);
+}
+
+static int ubiblock_getgeo(struct block_device *bdev, struct hd_geometry *geo)
+{
+	/* Some tools might require this information */
+	geo->heads = 1;
+	geo->cylinders = 1;
+	geo->sectors = get_capacity(bdev->bd_disk);
+	geo->start = 0;
+	return 0;
+}
+
+static const struct block_device_operations ubiblock_ops = {
+	.owner = THIS_MODULE,
+	.open = ubiblock_open,
+	.release = ubiblock_release,
+	.getgeo	= ubiblock_getgeo,
+};
+
+int ubiblock_add(struct ubi_volume_info *vi)
+{
+	struct ubiblock *dev;
+	struct gendisk *gd;
+	int disk_capacity;
+	int ret;
+
+	/* Check that the volume isn't already handled */
+	mutex_lock(&devices_mutex);
+	if (find_dev_nolock(vi->ubi_num, vi->vol_id)) {
+		mutex_unlock(&devices_mutex);
+		return -EEXIST;
+	}
+	mutex_unlock(&devices_mutex);
+
+	dev = kzalloc(sizeof(struct ubiblock), GFP_KERNEL);
+	if (!dev)
+		return -ENOMEM;
+
+	mutex_init(&dev->dev_mutex);
+
+	dev->ubi_num = vi->ubi_num;
+	dev->vol_id = vi->vol_id;
+	dev->leb_size = vi->usable_leb_size;
+
+	/* Initialize the gendisk of this ubiblock device */
+	gd = alloc_disk(1);
+	if (!gd) {
+		ubi_err("block: alloc_disk failed");
+		ret = -ENODEV;
+		goto out_free_dev;
+	}
+
+	gd->fops = &ubiblock_ops;
+	gd->major = ubiblock_major;
+	gd->first_minor = dev->ubi_num * UBI_MAX_VOLUMES + dev->vol_id;
+	gd->private_data = dev;
+	sprintf(gd->disk_name, "ubiblock%d_%d", dev->ubi_num, dev->vol_id);
+	disk_capacity = (vi->size * vi->usable_leb_size) >> 9;
+	set_capacity(gd, disk_capacity);
+	dev->gd = gd;
+
+	spin_lock_init(&dev->queue_lock);
+	dev->rq = blk_init_queue(ubiblock_request, &dev->queue_lock);
+	if (!dev->rq) {
+		ubi_err("block: blk_init_queue failed");
+		ret = -ENODEV;
+		goto out_put_disk;
+	}
+
+	dev->rq->queuedata = dev;
+	dev->gd->queue = dev->rq;
+
+	/*
+	 * Create one workqueue per volume (per registered block device).
+	 * Rembember workqueues are cheap, they're not threads.
+	 */
+	dev->wq = alloc_workqueue(gd->disk_name, 0, 0);
+	if (!dev->wq)
+		goto out_free_queue;
+	INIT_WORK(&dev->work, ubiblock_do_work);
+
+	mutex_lock(&devices_mutex);
+	list_add_tail(&dev->list, &ubiblock_devices);
+	mutex_unlock(&devices_mutex);
+
+	/* Must be the last step: anyone can call file ops from now on */
+	add_disk(dev->gd);
+
+	ubi_msg("%s created from ubi%d:%d(%s)",
+		dev->gd->disk_name, dev->ubi_num, dev->vol_id, vi->name);
+
+	return 0;
+
+out_free_queue:
+	blk_cleanup_queue(dev->rq);
+out_put_disk:
+	put_disk(dev->gd);
+out_free_dev:
+	kfree(dev);
+
+	return ret;
+}
+
+static void ubiblock_cleanup(struct ubiblock *dev)
+{
+	del_gendisk(dev->gd);
+	blk_cleanup_queue(dev->rq);
+	ubi_msg("%s released", dev->gd->disk_name);
+	put_disk(dev->gd);
+}
+
+int ubiblock_del(struct ubi_volume_info *vi)
+{
+	struct ubiblock *dev;
+
+	mutex_lock(&devices_mutex);
+	dev = find_dev_nolock(vi->ubi_num, vi->vol_id);
+	if (!dev) {
+		mutex_unlock(&devices_mutex);
+		return -ENODEV;
+	}
+
+	/* Found a device, let's lock it so we can check if it's busy */
+	mutex_lock(&dev->dev_mutex);
+
+	if (dev->refcnt > 0) {
+		mutex_unlock(&dev->dev_mutex);
+		mutex_unlock(&devices_mutex);
+		return -EBUSY;
+	}
+
+	/* Remove from device list */
+	list_del(&dev->list);
+	mutex_unlock(&devices_mutex);
+
+	/* Flush pending work and stop this workqueue */
+	destroy_workqueue(dev->wq);
+
+	ubiblock_cleanup(dev);
+	mutex_unlock(&dev->dev_mutex);
+	kfree(dev);
+	return 0;
+}
+
+static void ubiblock_resize(struct ubi_volume_info *vi)
+{
+	struct ubiblock *dev;
+	int disk_capacity;
+
+	/*
+	 * Need to lock the device list until we stop using the device,
+	 * otherwise the device struct might get released in ubiblock_del().
+	 */
+	mutex_lock(&devices_mutex);
+	dev = find_dev_nolock(vi->ubi_num, vi->vol_id);
+	if (!dev) {
+		mutex_unlock(&devices_mutex);
+		return;
+	}
+
+	mutex_lock(&dev->dev_mutex);
+	disk_capacity = (vi->size * vi->usable_leb_size) >> 9;
+	set_capacity(dev->gd, disk_capacity);
+	ubi_msg("%s resized to %d LEBs", dev->gd->disk_name, vi->size);
+	mutex_unlock(&dev->dev_mutex);
+	mutex_unlock(&devices_mutex);
+}
+
+static int ubiblock_notify(struct notifier_block *nb,
+			 unsigned long notification_type, void *ns_ptr)
+{
+	struct ubi_notification *nt = ns_ptr;
+
+	switch (notification_type) {
+	case UBI_VOLUME_ADDED:
+		/*
+		 * We want to enforce explicit block device attaching for
+		 * volumes; so when a volume is added we do nothing.
+		 */
+		break;
+	case UBI_VOLUME_REMOVED:
+		ubiblock_del(&nt->vi);
+		break;
+	case UBI_VOLUME_RESIZED:
+		ubiblock_resize(&nt->vi);
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block ubiblock_notifier = {
+	.notifier_call = ubiblock_notify,
+};
+
+static struct ubi_volume_desc * __init
+open_volume_desc(const char *name, int ubi_num, int vol_id)
+{
+	if (ubi_num == -1)
+		/* No ubi num, name must be a vol device path */
+		return ubi_open_volume_path(name, UBI_READONLY);
+	else if (vol_id == -1)
+		/* No vol_id, must be vol_name */
+		return ubi_open_volume_nm(ubi_num, name, UBI_READONLY);
+	else
+		return ubi_open_volume(ubi_num, vol_id, UBI_READONLY);
+}
+
+static int __init ubiblock_attach_from_param(void)
+{
+	int i, ret;
+	struct ubiblock_param *p;
+	struct ubi_volume_desc *desc;
+	struct ubi_volume_info vi;
+
+	for (i = 0; i < ubiblock_devs; i++) {
+		p = &ubiblock_param[i];
+
+		desc = open_volume_desc(p->name, p->ubi_num, p->vol_id);
+		if (IS_ERR(desc)) {
+			ubi_err("block: can't open volume, err=%ld\n",
+				PTR_ERR(desc));
+			ret = PTR_ERR(desc);
+			break;
+		}
+
+		ubi_get_volume_info(desc, &vi);
+		ubi_close_volume(desc);
+
+		ret = ubiblock_add(&vi);
+		if (ret) {
+			ubi_err("block: can't add '%s' volume, err=%d\n",
+				vi.name, ret);
+			break;
+		}
+	}
+	return ret;
+}
+
+static void ubiblock_detach_all(void)
+{
+	struct ubiblock *next;
+	struct ubiblock *dev;
+
+	list_for_each_entry_safe(dev, next, &ubiblock_devices, list) {
+
+		/* Flush pending work and stop workqueue */
+		destroy_workqueue(dev->wq);
+
+		/* The module is being forcefully removed */
+		WARN_ON(dev->desc);
+
+		/* Remove from device list */
+		list_del(&dev->list);
+
+		ubiblock_cleanup(dev);
+
+		kfree(dev);
+	}
+}
+
+int __init ubiblock_init(void)
+{
+	int ret;
+
+	ubiblock_major = register_blkdev(0, "ubiblock");
+	if (ubiblock_major < 0)
+		return ubiblock_major;
+
+	/* Attach block devices from 'block=' module param */
+	ret = ubiblock_attach_from_param();
+	if (ret)
+		goto err_detach;
+
+	/*
+	 * Block devices needs to be attached to volumes explicitly
+	 * upon user request. So we ignore existing volumes.
+	 */
+	ret = ubi_register_volume_notifier(&ubiblock_notifier, 1);
+	if (ret)
+		goto err_unreg;
+	return 0;
+
+err_unreg:
+	unregister_blkdev(ubiblock_major, "ubiblock");
+err_detach:
+	ubiblock_detach_all();
+	return ret;
+}
+
+void __exit ubiblock_exit(void)
+{
+	ubi_unregister_volume_notifier(&ubiblock_notifier);
+
+	ubiblock_detach_all();
+
+	unregister_blkdev(ubiblock_major, "ubiblock");
+}
diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 57deae9..6e30a3c 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -1298,6 +1298,15 @@ static int __init ubi_init(void)
 		}
 	}
 
+	err = ubiblock_init();
+	if (err) {
+		ubi_err("block: cannot initialize, error %d", err);
+
+		/* See comment above re-ubi_is_module(). */
+		if (ubi_is_module())
+			goto out_detach;
+	}
+
 	return 0;
 
 out_detach:
@@ -1326,6 +1335,8 @@ static void __exit ubi_exit(void)
 {
 	int i;
 
+	ubiblock_exit();
+
 	for (i = 0; i < UBI_MAX_DEVICES; i++)
 		if (ubi_devices[i]) {
 			mutex_lock(&ubi_devices_mutex);
diff --git a/drivers/mtd/ubi/cdev.c b/drivers/mtd/ubi/cdev.c
index 8ca49f2..39d3774 100644
--- a/drivers/mtd/ubi/cdev.c
+++ b/drivers/mtd/ubi/cdev.c
@@ -561,6 +561,26 @@ static long vol_cdev_ioctl(struct file *file, unsigned int cmd,
 		break;
 	}
 
+	/* Attach a block device to an UBI volume */
+	case UBI_IOCVOLATTBLK:
+	{
+		struct ubi_volume_info vi;
+
+		ubi_get_volume_info(desc, &vi);
+		err = ubiblock_add(&vi);
+		break;
+	}
+
+	/* Dettach a block device from an UBI volume */
+	case UBI_IOCVOLDETBLK:
+	{
+		struct ubi_volume_info vi;
+
+		ubi_get_volume_info(desc, &vi);
+		err = ubiblock_del(&vi);
+		break;
+	}
+
 	default:
 		err = -ENOTTY;
 		break;
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index 8ea6297..e76ff98 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -864,6 +864,20 @@ int ubi_update_fastmap(struct ubi_device *ubi);
 int ubi_scan_fastmap(struct ubi_device *ubi, struct ubi_attach_info *ai,
 		     int fm_anchor);
 
+/* block.c */
+#ifdef CONFIG_MTD_UBI_BLOCK
+int ubiblock_init(void);
+void ubiblock_exit(void);
+int ubiblock_add(struct ubi_volume_info *vi);
+int ubiblock_del(struct ubi_volume_info *vi);
+#else
+static inline int ubiblock_init(void) { return 0; }
+static inline void ubiblock_exit(void) {}
+static inline int ubiblock_add(struct ubi_volume_info *vi) { return -ENOTTY; }
+static inline int ubiblock_del(struct ubi_volume_info *vi) { return -ENOTTY; }
+#endif
+
+
 /*
  * ubi_rb_for_each_entry - walk an RB-tree.
  * @rb: a pointer to type 'struct rb_node' to use as a loop counter
diff --git a/include/uapi/mtd/ubi-user.h b/include/uapi/mtd/ubi-user.h
index 723c324..b98585a 100644
--- a/include/uapi/mtd/ubi-user.h
+++ b/include/uapi/mtd/ubi-user.h
@@ -134,6 +134,13 @@
  * used. A pointer to a &struct ubi_set_vol_prop_req object is expected to be
  * passed. The object describes which property should be set, and to which value
  * it should be set.
+ *
+ * Block devices on UBI volumes
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * To attach or detach a block device from an UBI volume the %UBI_IOCVOLATTBLK
+ * and %UBI_IOCVOLDETBLK ioctl commands should be used, respectively.
+ * These commands take no arguments.
  */
 
 /*
@@ -191,6 +198,10 @@
 /* Set an UBI volume property */
 #define UBI_IOCSETVOLPROP _IOW(UBI_VOL_IOC_MAGIC, 6, \
 			       struct ubi_set_vol_prop_req)
+/* Attach a block device to an UBI volume */
+#define UBI_IOCVOLATTBLK _IO(UBI_VOL_IOC_MAGIC, 7)
+/* Detach a block device from an UBI volume */
+#define UBI_IOCVOLDETBLK _IO(UBI_VOL_IOC_MAGIC, 8)
 
 /* Maximum MTD device name length supported by UBI */
 #define MAX_UBI_MTD_NAME_LEN 127
-- 
1.8.1.5

[PATCH v7 2/3] ubi-utils: Add ubiblock tool

[Ezequiel Garcia]

With the addition of block device access to UBI volumes, we now
add a simple userspace tool to access the new ioctls.

Since the ioctls have no arguments, usage of this tool is as simple
as it gets:

  $ ubiblock --attach /dev/ubi0_0

will make a new device /dev/ubiblock0_0 available, and

  $ ubiblock --detach /dev/ubi0_0

will remove the device.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
---
 Makefile                   |   2 +-
 include/mtd/ubi-user.h     |   4 ++
 ubi-utils/.gitignore       |   1 +
 ubi-utils/include/libubi.h |  16 +++++
 ubi-utils/libubi.c         |  10 +++
 ubi-utils/ubiblock.c       | 176 +++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 208 insertions(+), 1 deletion(-)
 create mode 100644 ubi-utils/ubiblock.c

diff --git a/Makefile b/Makefile
index 4ff8a49..d316a3d 100644
--- a/Makefile
+++ b/Makefile
@@ -28,7 +28,7 @@ MTD_BINS = \
 	sumtool jffs2reader
 UBI_BINS = \
 	ubiupdatevol ubimkvol ubirmvol ubicrc32 ubinfo ubiattach \
-	ubidetach ubinize ubiformat ubirename mtdinfo ubirsvol
+	ubidetach ubinize ubiformat ubirename mtdinfo ubirsvol ubiblock
 
 BINS = $(MTD_BINS)
 BINS += mkfs.ubifs/mkfs.ubifs
diff --git a/include/mtd/ubi-user.h b/include/mtd/ubi-user.h
index 1c06d88..1889249 100644
--- a/include/mtd/ubi-user.h
+++ b/include/mtd/ubi-user.h
@@ -186,6 +186,10 @@
 /* Set an UBI volume property */
 #define UBI_IOCSETVOLPROP _IOW(UBI_VOL_IOC_MAGIC, 6, \
 			       struct ubi_set_vol_prop_req)
+/* Attach a block device to an UBI volume */
+#define UBI_IOCVOLATTBLK _IO(UBI_VOL_IOC_MAGIC, 7)
+/* Detach a block device from an UBI volume */
+#define UBI_IOCVOLDETBLK _IO(UBI_VOL_IOC_MAGIC, 8)
 
 /* Maximum MTD device name length supported by UBI */
 #define MAX_UBI_MTD_NAME_LEN 127
diff --git a/ubi-utils/.gitignore b/ubi-utils/.gitignore
index c035c97..19653a8 100644
--- a/ubi-utils/.gitignore
+++ b/ubi-utils/.gitignore
@@ -9,4 +9,5 @@
 /ubirmvol
 /ubiupdatevol
 /ubirsvol
+/ubiblock
 /mtdinfo
diff --git a/ubi-utils/include/libubi.h b/ubi-utils/include/libubi.h
index 47f40e2..3759aa8 100644
--- a/ubi-utils/include/libubi.h
+++ b/ubi-utils/include/libubi.h
@@ -400,6 +400,22 @@ int ubi_get_vol_info1_nm(libubi_t desc, int dev_num, const char *name,
 			 struct ubi_vol_info *info);
 
 /**
+ * ubi_vol_block_add - attach a block device to an UBI volume.
+ * @fd: volume character device file descriptor
+ *
+ * Returns %0 in case of success and %-1 in case of failure.
+ */
+int ubi_vol_block_add(int fd);
+
+/**
+ * ubi_vol_block_del - detach a block device from an UBI volume.
+ * @fd: volume character device file descriptor
+ *
+ * Returns %0 in case of success and %-1 in case of failure.
+ */
+int ubi_vol_block_del(int fd);
+
+/**
  * ubi_update_start - start UBI volume update.
  * @desc: UBI library descriptor
  * @fd: volume character device file descriptor
diff --git a/ubi-utils/libubi.c b/ubi-utils/libubi.c
index a7463e8..cb631f9 100644
--- a/ubi-utils/libubi.c
+++ b/ubi-utils/libubi.c
@@ -1109,6 +1109,16 @@ int ubi_rsvol(libubi_t desc, const char *node, int vol_id, long long bytes)
 	return ret;
 }
 
+int ubi_vol_block_add(int fd)
+{
+	return ioctl(fd, UBI_IOCVOLATTBLK);
+}
+
+int ubi_vol_block_del(int fd)
+{
+	return ioctl(fd, UBI_IOCVOLDETBLK);
+}
+
 int ubi_update_start(libubi_t desc, int fd, long long bytes)
 {
 	desc = desc;
diff --git a/ubi-utils/ubiblock.c b/ubi-utils/ubiblock.c
new file mode 100644
index 0000000..b57e509
--- /dev/null
+++ b/ubi-utils/ubiblock.c
@@ -0,0 +1,176 @@
+/*
+ * ubiblock:
+ *   An utility to attach block devices to UBI volumes.
+ *
+ * Copyright (c) Ezequiel Garcia, 2014
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * Usage
+ * -----
+ * Since the ioctls have no arguments, usage of this tool is as simple
+ * as it gets:
+ *
+ *   $ ubiblock --attach /dev/ubi0_0
+ *
+ * will make a new device /dev/ubiblock0_0 available, and
+ *
+ *   $ ubiblock --detach /dev/ubi0_0
+ *
+ * will remove the device.
+ */
+
+#define PROGRAM_NAME    "ubiblock"
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <getopt.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+#include <libubi.h>
+#include "common.h"
+
+struct args {
+	const char *node;
+	int attach;
+};
+
+static struct args args;
+
+static const char doc[] = PROGRAM_NAME " version " VERSION
+			 " - a tool to add/remove block device interface from UBI volumes.";
+
+static const char optionsstr[] =
+"-a, --attach               attach block to volume\n"
+"-d, --detach               detach block from volume\n"
+"-h, --help                 print help message\n"
+"-V, --version              print program version";
+
+static const char usage[] =
+"Usage: " PROGRAM_NAME " [-a,-d] <UBI volume node file name>\n"
+"Example: " PROGRAM_NAME " --attach /dev/ubi0_0";
+
+static const struct option long_options[] = {
+	{ .name = "attach",   .has_arg = 1, .flag = NULL, .val = 'a' },
+	{ .name = "detach",   .has_arg = 1, .flag = NULL, .val = 'd' },
+	{ .name = "help",     .has_arg = 0, .flag = NULL, .val = 'h' },
+	{ .name = "version",  .has_arg = 0, .flag = NULL, .val = 'V' },
+	{ NULL, 0, NULL, 0}
+};
+
+static int parse_opt(int argc, char * const argv[])
+{
+	while (1) {
+		int key;
+
+		key = getopt_long(argc, argv, "a:d:h?V", long_options, NULL);
+		if (key == -1)
+			break;
+
+		switch (key) {
+		case 'a':
+			args.attach = 1;
+		case 'd':
+			args.node = optarg;
+			break;
+		case 'h':
+		case '?':
+			printf("%s\n\n", doc);
+			printf("%s\n\n", usage);
+			printf("%s\n", optionsstr);
+			exit(EXIT_SUCCESS);
+
+		case 'V':
+			common_print_version();
+			exit(EXIT_SUCCESS);
+
+		default:
+			fprintf(stderr, "Use -h for help\n");
+			return -1;
+		}
+	}
+
+	if (!args.node)
+		return errmsg("invalid arguments (use -h for help)");
+
+	return 0;
+}
+
+int main(int argc, char * const argv[])
+{
+	int err, fd;
+	libubi_t libubi;
+
+	err = parse_opt(argc, argv);
+	if (err)
+		return -1;
+
+	libubi = libubi_open();
+	if (!libubi) {
+		if (errno == 0)
+			errmsg("UBI is not present in the system");
+		else
+			sys_errmsg("cannot open libubi");
+		goto out_libubi;
+	}
+
+	err = ubi_probe_node(libubi, args.node);
+	if (err == 1) {
+		errmsg("\"%s\" is an UBI device node, not an UBI volume node",
+		       args.node);
+		goto out_libubi;
+	} else if (err < 0) {
+		if (errno == ENODEV)
+			errmsg("\"%s\" is not an UBI volume node", args.node);
+		else
+			sys_errmsg("error while probing \"%s\"", args.node);
+		goto out_libubi;
+	}
+
+	fd = open(args.node, O_RDWR);
+	if (fd == -1) {
+		sys_errmsg("cannot open UBI volume \"%s\"", args.node);
+		goto out_libubi;
+	}
+
+	if (args.attach) {
+		err = ubi_vol_block_add(fd);
+		if (err) {
+			sys_errmsg("cannot attach block device");
+			goto out_close;
+		}
+	} else {
+		err = ubi_vol_block_del(fd);
+		if (err) {
+			sys_errmsg("cannot detach block device");
+			goto out_close;
+		}
+	}
+
+	close(fd);
+	libubi_close(libubi);
+	return 0;
+
+out_close:
+	close(fd);
+out_libubi:
+	libubi_close(libubi);
+	return -1;
+}
-- 
1.8.1.5

[PATCH v7 3/3] Add UBI block interface documentation

[Ezequiel Garcia]

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
---
 doc/general.xml |  4 ++++
 doc/ubi.xml     | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 faq/ubi.xml     | 16 +++++++--------
 3 files changed, 73 insertions(+), 8 deletions(-)

diff --git a/doc/general.xml b/doc/general.xml
index 31ea243..06cb887 100644
--- a/doc/general.xml
+++ b/doc/general.xml
@@ -182,6 +182,10 @@ use block-based file systems on top of bare flashes using
 In other words, please, <b>do not use</b> <code>mtdblock</code> unless you
 know exactly what you are doing.</p>
 
+<p>Instead, you may find the block device emulation provided by <code>UBI</code>
+useful. Please refer to the <a href="ubi.html#L_block">UBI section</a> for more
+details.</p>
+
 <p>There is also a read-only version of this driver which doesn't have the
 capacity to do the caching and erase/writeback, mainly for use with uCLinux
 where the extra RAM requirement was considered too large.</p>
diff --git a/doc/ubi.xml b/doc/ubi.xml
index f55c04a..a65f18e 100644
--- a/doc/ubi.xml
+++ b/doc/ubi.xml
@@ -47,6 +47,7 @@
 		</ol>
 	</li>
 	<li><a href="ubi.html#L_fastmap">Fastmap</a></li>
+	<li><a href="ubi.html#L_block">Block device</a></li>
 	<li><a href="ubi.html#L_ubidoc">More documentation</a></li>
 </ol>
 
@@ -173,6 +174,10 @@ because:</p>
 	mechanisms).</li>
 </ul>
 
+<p>UBI also provides a block device that allows regular, block-oriented
+file systems to be mounted on top of an UBI volume. This is possible because UBI
+handles bad-blocks transparently.</p>
+
 <p>There is an additional driver called <code>gluebi</code> which emulates MTD
 devices on top of UBI volumes. This looks a little strange, because UBI works
 on top of an MTD device, then <code>gluebi</code> emulates other MTD devices
@@ -236,6 +241,8 @@ sub-directory.</p>
 	devices (the opposite to what <code>ubiattach</code> does);</li>
 	<li><code>ubimkvol</code> - creates UBI volumes on UBI devices;</li>
 	<li><code>ubirmvol</code> - removes UBI volumes from UBI devices;</li>
+	<li><code>ubiblock</code> - manages block interfaces for UBI volumes.
+	See <a href="ubi.html#L_block">here</a> for more information;</li>
 	<li><code>ubiupdatevol</code> - updates UBI volumes; this tool uses the
 	<a href="ubi.html#L_volupdate">UBI volume update feature</a> which
 	leaves the volume in "corrupted" state if the update was interrupted;
@@ -1261,6 +1268,60 @@ second. Therefore, fastmap makes only sense on fast and large flash devices
 where a full scan takes too long. E.g. On 4GiB NAND chips a full scan takes
 several seconds whereas a fast attach needs less than one second.</p>
 
+<h2><a name="L_block">Read-only block device access</a></h2>
+
+<p>UBI allows to create a block device on top of each UBI volume. The block
+device implementation currently has the following limitations:
+
+<ul>
+	<li>Read-only operation.</li>
+	<li>Serialized operation.</li>
+	<li>1-to-1 mapping between block sectors and logical eraseblocks.
+	In other words, no wear-leveling is provided.</li>
+</ul></p>
+
+<p>Keep in mind the NAND driver core already serializes all I/O anyway,
+so it's not expected this limitation will affect performance.</p>
+
+<p>Despite these limitations, a block device is still very useful to mount
+read-only, regular file systems on top of UBI volumes. This is the case
+of squashfs, which can be used as a lightweigth read-only rootfs on a NAND
+device.</p>
+
+<h4><a name="L_block_usage">Usage</a></h4>
+<p>Attaching and detaching a block device on a UBI volume is fairly easy.
+You can do this either by using the <code>block</code> UBI module parameter
+or with the <code>ubiblock</code> user-space tool.</p>
+
+<p>In order to attach a block device on bootup time (e.g. to mount the rootfs
+on such a block device) you can specify the <code>block</code> parameter as
+a kernel boot arguments:</p>
+
+<p><code>ubi.mtd=5 ubi.block=0,0 root=/dev/ubiblock0_0</code></p>
+
+<p>There are several ways if specifying a volume:</p>
+<ul>
+	<li><p>Using the UBI volume path:</p>
+	<code>ubi.block=/dev/ubi0_0</code></li>
+
+	<li><p>Using the UBI device, and the volume name:</p>
+	<code>ubi.block=0,rootfs</code></li>
+
+	<li><p>Using both UBI device number and UBI volume number:</p>
+	<code>ubi.block=0,0</code></li>
+</ul>
+
+<p>If you've built UBI as a module you can use this parameter at module insertion
+time:</p>
+
+<code>$ modprobe ubi mtd=/dev/mtd5 block=/dev/ubi0_0</code>
+
+<p>A block device can also be attached/detached dynamically at runtime, using
+the <code>ubiblock</code> user-space tool:</p>
+
+<p><code>$ ubiblock --attach /dev/ubi0_0</code></p>
+<p><code>$ ubiblock --detach /dev/ubi0_0</code></p>
+
 <h2><a name="L_ubidoc">More documentation</a></h2>
 
 <p>Unfortunately, there are no thorough and strict UBI documents. But there is
diff --git a/faq/ubi.xml b/faq/ubi.xml
index 2832928..e207862 100644
--- a/faq/ubi.xml
+++ b/faq/ubi.xml
@@ -18,6 +18,7 @@
 	<li><a href="ubi.html#L_mkvol">How do I create/delete UBI volumes?</a></li>
 	<li><a href="ubi.html#L_run_jffs2">How do I run JFFS2 on top of an UBI volume?</a></li>
 	<li><a href="ubi.html#L_ext2_over_ubi">Can I run ext2 on top of UBI?</a></li>
+	<li><a href="ubi.html#L_squashfs_over_ubi">Can I run squashfs on top of UBI?</a></li>
 	<li><a href="ubi.html#L_format_mtd">Do I have to format my empty flash before running UBI on top of it?</a></li>
 	<li><a href="ubi.html#L_ubierase">How do I erase flash and preserve erase counters?</a></li>
 	<li><a href="ubi.html#L_ubi_mkimg">How do I create UBI images?</a></li>
@@ -159,16 +160,15 @@ Please, read the <a href="../doc/ubi.html#L_rednote">big red note</a>
 and <a href="../doc/ubi.html#L_overview">overview</a> documentation sections to
 realize why.</p>
 
-<p>But it is much easier to implement FTL on top of UBI than on top of MTD,
-because UBI takes care about many flash complexities and makes it
-possible to concentrate on on upper-level issues rather then solving flash
-media problems like wear-leveling, bit-flips, bad eraseblocks, etc.</p>
-
-<p><a
-href="http://lists.infradead.org/pipermail/linux-mtd/2008-January/020381.html">
-This</a> e-mail describes an idea of a simple FTL layer on top of UBI.</p>
+<p>However, given UBI takes care of many flash complexities, it provides a
+bad-block-free block device access on top of UBI volumes. This feature is useful to
+mount read-only file systems.</p>
 
+<h2><a name="L_squashfs_over_ubi">Can I run squashfs on top of UBI?</a></h2>
 
+<p>Yes. UBI allows to create a read-only block device on top of a UBI volume
+which is suitable for read-only, block-oriented file systems, such as squashfs.
+See the <a href="..doc/ubi.html#L_block">UBI block device</a> section for more details.</p>
 
 <h2><a name="L_format_mtd">
 	Do I have to format my empty flash before running UBI on top of it?
-- 
1.8.1.5

[PATCH v8] ubi: Introduce read-only block devices on top of UBI volumes

[Ezequiel Garcia]

This commit introduces read-only block device emulation on top of UBI volumes.

Given UBI takes care of wear leveling and bad block management it's possible
to add a thin layer to enable block device access to UBI volumes.
This allows to use a block-oriented filesystem on a flash device.

The UBI block devices are meant to be used in conjunction with any
regular, block-oriented file system (e.g. ext4), although it's primarily
targeted at read-only file systems, such as squashfs.

Block devices are created upon user request through new ioctls:
UBI_IOCVOLATTBLK to attach and UBI_IOCVOLDETBLK to detach.
Also, a new UBI module parameter is added 'ubi.block'. This parameter is
needed in order to attach a block device on boot-up time, allowing to
mount the rootfs on a ubiblock device.
For instance, you could have these kernel parameters:

  ubi.mtd=5 ubi.block=0,0 root=/dev/ubiblock0_0

Or, if you compile ubi as a module:

  $ modprobe ubi mtd=/dev/mtd5 block=/dev/ubi0_0

Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Brian Norris <computersforpeace@gmail.com>
Cc: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Piergiorgio Beruto <piergiorgio.beruto@gmail.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Richard Weinberger <richard.weinberger@gmail.com>
Cc: Boris BREZILLON <b.brezillon.dev@gmail.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
---
Changes from v7:

  * Added copyright notice for the parameter handling code.

  * Removed unused ubi_volume_info pointer. Thanks to Boris Brezillon
    for noticing this!

 drivers/mtd/ubi/Kconfig     |  15 +
 drivers/mtd/ubi/Makefile    |   1 +
 drivers/mtd/ubi/block.c     | 663 ++++++++++++++++++++++++++++++++++++++++++++
 drivers/mtd/ubi/build.c     |  11 +
 drivers/mtd/ubi/cdev.c      |  20 ++
 drivers/mtd/ubi/ubi.h       |  14 +
 include/uapi/mtd/ubi-user.h |  11 +
 7 files changed, 735 insertions(+)
 create mode 100644 drivers/mtd/ubi/block.c

diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index 36663af..783fb18 100644
--- a/drivers/mtd/ubi/Kconfig
+++ b/drivers/mtd/ubi/Kconfig
@@ -87,4 +87,19 @@ config MTD_UBI_GLUEBI
 	   work on top of UBI. Do not enable this unless you use legacy
 	   software.
 
+config MTD_UBI_BLOCK
+	bool "Read-only block devices on top of UBI volumes"
+	default n
+	help
+	   This option enables read-only UBI block devices support. UBI block
+	   devices will be layered on top of UBI volumes, which means that the
+	   UBI driver will transparently handle things like bad eraseblocks and
+	   bit-flips. You can put any block-oriented file system on top of UBI
+	   volumes in read-only mode (e.g., ext4), but it is probably most
+	   practical for read-only file systems, like squashfs.
+
+	   When selected, this feature will be built in the UBI driver.
+
+	   If in doubt, say "N".
+
 endif # MTD_UBI
diff --git a/drivers/mtd/ubi/Makefile b/drivers/mtd/ubi/Makefile
index b46b0c97..4e3c3d7 100644
--- a/drivers/mtd/ubi/Makefile
+++ b/drivers/mtd/ubi/Makefile
@@ -3,5 +3,6 @@ obj-$(CONFIG_MTD_UBI) += ubi.o
 ubi-y += vtbl.o vmt.o upd.o build.o cdev.o kapi.o eba.o io.o wl.o attach.o
 ubi-y += misc.o debug.o
 ubi-$(CONFIG_MTD_UBI_FASTMAP) += fastmap.o
+ubi-$(CONFIG_MTD_UBI_BLOCK) += block.o
 
 obj-$(CONFIG_MTD_UBI_GLUEBI) += gluebi.o
diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
new file mode 100644
index 0000000..16cbf49
--- /dev/null
+++ b/drivers/mtd/ubi/block.c
@@ -0,0 +1,663 @@
+/*
+ * Copyright (c) 2014 Ezequiel Garcia
+ * Copyright (c) 2011 Free Electrons
+ *
+ * Driver parameter handling strongly based on drivers/mtd/ubi/build.c
+ *   Copyright (c) International Business Machines Corp., 2006
+ *   Copyright (c) Nokia Corporation, 2007
+ *   Authors: Artem Bityutskiy (Битюцкий Артём), Frank Haverkamp
+ *
+ * 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, version 2.
+ *
+ * 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.
+ */
+
+/*
+ * Read-only block devices on top of UBI volumes
+ *
+ * A simple implementation to allow a block device to be layered on top of a
+ * UBI volume. The implementation is provided by creating a static 1-to-1
+ * mapping between the block device and the UBI volume.
+ *
+ * The addressed byte is obtained from the addressed block sector, which is
+ * mapped linearly into the corresponding LEB:
+ *
+ *   leb number = addressed byte / leb size
+ *
+ * This feature is compiled in the UBI core, and adds a new 'block' parameter
+ * to allow early block device attaching. Runtime  block attach/detach for UBI
+ * volumes is provided through two new UBI ioctls: UBI_IOCVOLATTBLK and
+ * UBI_IOCVOLDETBLK.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/mtd/ubi.h>
+#include <linux/workqueue.h>
+#include <linux/blkdev.h>
+#include <linux/hdreg.h>
+#include <asm/div64.h>
+
+#include "ubi-media.h"
+#include "ubi.h"
+
+/* Maximum number of supported devices */
+#define UBIBLOCK_MAX_DEVICES 32
+
+/* Maximum length of the 'block=' parameter */
+#define UBIBLOCK_PARAM_LEN 63
+
+/* Maximum number of comma-separated items in the 'block=' parameter */
+#define UBIBLOCK_PARAM_COUNT 2
+
+struct ubiblock_param {
+	int ubi_num;
+	int vol_id;
+	char name[UBIBLOCK_PARAM_LEN+1];
+};
+
+/* Numbers of elements set in the @ubiblock_param array */
+static int ubiblock_devs __initdata;
+
+/* MTD devices specification parameters */
+static struct ubiblock_param ubiblock_param[UBIBLOCK_MAX_DEVICES] __initdata;
+
+struct ubiblock {
+	struct ubi_volume_desc *desc;
+	int ubi_num;
+	int vol_id;
+	int refcnt;
+	int leb_size;
+
+	struct gendisk *gd;
+	struct request_queue *rq;
+
+	struct workqueue_struct *wq;
+	struct work_struct work;
+
+	struct mutex dev_mutex;
+	spinlock_t queue_lock;
+	struct list_head list;
+};
+
+/* Linked list of all ubiblock instances */
+static LIST_HEAD(ubiblock_devices);
+static DEFINE_MUTEX(devices_mutex);
+static int ubiblock_major;
+
+static int __init ubiblock_set_param(const char *val,
+				     const struct kernel_param *kp)
+{
+	int i, ret;
+	size_t len;
+	struct ubiblock_param *param;
+	char buf[UBIBLOCK_PARAM_LEN];
+	char *pbuf = &buf[0];
+	char *tokens[UBIBLOCK_PARAM_COUNT];
+
+	if (!val)
+		return -EINVAL;
+
+	len = strnlen(val, UBIBLOCK_PARAM_LEN);
+	if (len == 0) {
+		ubi_warn("block: empty 'block=' parameter - ignored\n");
+		return 0;
+	}
+
+	if (len == UBIBLOCK_PARAM_LEN) {
+		ubi_err("block: parameter \"%s\" is too long, max. is %d\n",
+			val, UBIBLOCK_PARAM_LEN);
+		return -EINVAL;
+	}
+
+	strcpy(buf, val);
+
+	/* Get rid of the final newline */
+	if (buf[len - 1] == '\n')
+		buf[len - 1] = '\0';
+
+	for (i = 0; i < UBIBLOCK_PARAM_COUNT; i++)
+		tokens[i] = strsep(&pbuf, ",");
+
+	param = &ubiblock_param[ubiblock_devs];
+	if (tokens[1]) {
+		/* Two parameters: can be 'ubi, vol_id' or 'ubi, vol_name' */
+		ret = kstrtoint(tokens[0], 10, &param->ubi_num);
+		if (ret < 0)
+			return -EINVAL;
+
+		/* Second param can be a number or a name */
+		ret = kstrtoint(tokens[1], 10, &param->vol_id);
+		if (ret < 0) {
+			param->vol_id = -1;
+			strcpy(param->name, tokens[1]);
+		}
+
+	} else {
+		/* One parameter: must be device path */
+		strcpy(param->name, tokens[0]);
+		param->ubi_num = -1;
+		param->vol_id = -1;
+	}
+
+	ubiblock_devs++;
+
+	return 0;
+}
+
+static const struct kernel_param_ops ubiblock_param_ops = {
+	.set    = ubiblock_set_param,
+};
+module_param_cb(block, &ubiblock_param_ops, NULL, 0);
+MODULE_PARM_DESC(block, "Attach block devices to UBI volumes. Parameter format: block=<path|dev,num|dev,name>.\n"
+			"Multiple \"block\" parameters may be specified.\n"
+			"UBI volumes may be specified by their number, name, or path to the device node.\n"
+			"Examples\n"
+			"Using the UBI volume path:\n"
+			"ubi.block=/dev/ubi0_0\n"
+			"Using the UBI device, and the volume name:\n"
+			"ubi.block=0,rootfs\n"
+			"Using both UBI device number and UBI volume number:\n"
+			"ubi.block=0,0\n");
+
+static struct ubiblock *find_dev_nolock(int ubi_num, int vol_id)
+{
+	struct ubiblock *dev;
+
+	list_for_each_entry(dev, &ubiblock_devices, list)
+		if (dev->ubi_num == ubi_num && dev->vol_id == vol_id)
+			return dev;
+	return NULL;
+}
+
+static int ubiblock_read_to_buf(struct ubiblock *dev, char *buffer,
+				int leb, int offset, int len)
+{
+	int ret;
+
+	ret = ubi_read(dev->desc, leb, buffer, offset, len);
+	if (ret) {
+		ubi_err("%s ubi_read error %d",
+			dev->gd->disk_name, ret);
+		return ret;
+	}
+	return 0;
+}
+
+static int ubiblock_read(struct ubiblock *dev, char *buffer,
+			 sector_t sec, int len)
+{
+	int ret, leb, offset;
+	int bytes_left = len;
+	int to_read = len;
+	loff_t pos = sec << 9;
+
+	/* Get leb:offset address to read from */
+	offset = do_div(pos, dev->leb_size);
+	leb = pos;
+
+	while (bytes_left) {
+
+		/*
+		 * We can only read one leb at a time.
+		 * Therefore if the read length is larger than
+		 * one leb size, we split the operation.
+		 */
+		if (offset + to_read > dev->leb_size)
+			to_read = dev->leb_size - offset;
+
+		ret = ubiblock_read_to_buf(dev, buffer, leb, offset, to_read);
+		if (ret)
+			return ret;
+
+		buffer += to_read;
+		bytes_left -= to_read;
+		to_read = bytes_left;
+		leb++;
+		offset = 0;
+	}
+	return 0;
+}
+
+static int do_ubiblock_request(struct ubiblock *dev, struct request *req)
+{
+	int len, ret;
+	sector_t sec;
+
+	if (req->cmd_type != REQ_TYPE_FS)
+		return -EIO;
+
+	if (blk_rq_pos(req) + blk_rq_cur_sectors(req) >
+	    get_capacity(req->rq_disk))
+		return -EIO;
+
+	if (rq_data_dir(req) != READ)
+		return -ENOSYS; /* Write not implemented */
+
+	sec = blk_rq_pos(req);
+	len = blk_rq_cur_bytes(req);
+
+	/*
+	 * Let's prevent the device from being removed while we're doing I/O
+	 * work. Notice that this means we serialize all the I/O operations,
+	 * but it's probably of no impact given the NAND core serializes
+	 * flash acceses anywafy.
+	 */
+	mutex_lock(&dev->dev_mutex);
+	ret = ubiblock_read(dev, req->buffer, sec, len);
+	mutex_unlock(&dev->dev_mutex);
+
+	return ret;
+}
+
+static void ubiblock_do_work(struct work_struct *work)
+{
+	struct ubiblock *dev =
+		container_of(work, struct ubiblock, work);
+	struct request_queue *rq = dev->rq;
+	struct request *req;
+	int res;
+
+	spin_lock_irq(rq->queue_lock);
+
+	req = blk_fetch_request(rq);
+	while (req) {
+
+		spin_unlock_irq(rq->queue_lock);
+		res = do_ubiblock_request(dev, req);
+		spin_lock_irq(rq->queue_lock);
+
+		/*
+		 * If we're done with this request,
+		 * we need to fetch a new one
+		 */
+		if (!__blk_end_request_cur(req, res))
+			req = blk_fetch_request(rq);
+	}
+
+	spin_unlock_irq(rq->queue_lock);
+}
+
+static void ubiblock_request(struct request_queue *rq)
+{
+	struct ubiblock *dev;
+	struct request *req;
+
+	dev = rq->queuedata;
+
+	if (!dev)
+		while ((req = blk_fetch_request(rq)) != NULL)
+			__blk_end_request_all(req, -ENODEV);
+	else
+		queue_work(dev->wq, &dev->work);
+}
+
+static int ubiblock_open(struct block_device *bdev, fmode_t mode)
+{
+	struct ubiblock *dev = bdev->bd_disk->private_data;
+	int ret;
+
+	mutex_lock(&dev->dev_mutex);
+	if (dev->refcnt > 0) {
+		/*
+		 * The volume is already open, just increase the reference
+		 * counter.
+		 */
+		goto out_done;
+	}
+
+	/*
+	 * We want users to be aware they should only mount us as read-only.
+	 * It's just a paranoid check, as write requests will get rejected
+	 * in any case.
+	 */
+	if (mode & FMODE_WRITE) {
+		ret = -EPERM;
+		goto out_unlock;
+	}
+
+	dev->desc = ubi_open_volume(dev->ubi_num, dev->vol_id, UBI_READONLY);
+	if (IS_ERR(dev->desc)) {
+		ubi_err("%s failed to open ubi volume %d_%d",
+			dev->gd->disk_name, dev->ubi_num, dev->vol_id);
+		ret = PTR_ERR(dev->desc);
+		dev->desc = NULL;
+		goto out_unlock;
+	}
+
+out_done:
+	dev->refcnt++;
+	mutex_unlock(&dev->dev_mutex);
+	return 0;
+
+out_close:
+	ubi_close_volume(dev->desc);
+	dev->desc = NULL;
+out_unlock:
+	mutex_unlock(&dev->dev_mutex);
+	return ret;
+}
+
+static void ubiblock_release(struct gendisk *gd, fmode_t mode)
+{
+	struct ubiblock *dev = gd->private_data;
+
+	mutex_lock(&dev->dev_mutex);
+
+	dev->refcnt--;
+	if (dev->refcnt == 0) {
+		ubi_close_volume(dev->desc);
+		dev->desc = NULL;
+	}
+
+	mutex_unlock(&dev->dev_mutex);
+}
+
+static int ubiblock_getgeo(struct block_device *bdev, struct hd_geometry *geo)
+{
+	/* Some tools might require this information */
+	geo->heads = 1;
+	geo->cylinders = 1;
+	geo->sectors = get_capacity(bdev->bd_disk);
+	geo->start = 0;
+	return 0;
+}
+
+static const struct block_device_operations ubiblock_ops = {
+	.owner = THIS_MODULE,
+	.open = ubiblock_open,
+	.release = ubiblock_release,
+	.getgeo	= ubiblock_getgeo,
+};
+
+int ubiblock_add(struct ubi_volume_info *vi)
+{
+	struct ubiblock *dev;
+	struct gendisk *gd;
+	int disk_capacity;
+	int ret;
+
+	/* Check that the volume isn't already handled */
+	mutex_lock(&devices_mutex);
+	if (find_dev_nolock(vi->ubi_num, vi->vol_id)) {
+		mutex_unlock(&devices_mutex);
+		return -EEXIST;
+	}
+	mutex_unlock(&devices_mutex);
+
+	dev = kzalloc(sizeof(struct ubiblock), GFP_KERNEL);
+	if (!dev)
+		return -ENOMEM;
+
+	mutex_init(&dev->dev_mutex);
+
+	dev->ubi_num = vi->ubi_num;
+	dev->vol_id = vi->vol_id;
+	dev->leb_size = vi->usable_leb_size;
+
+	/* Initialize the gendisk of this ubiblock device */
+	gd = alloc_disk(1);
+	if (!gd) {
+		ubi_err("block: alloc_disk failed");
+		ret = -ENODEV;
+		goto out_free_dev;
+	}
+
+	gd->fops = &ubiblock_ops;
+	gd->major = ubiblock_major;
+	gd->first_minor = dev->ubi_num * UBI_MAX_VOLUMES + dev->vol_id;
+	gd->private_data = dev;
+	sprintf(gd->disk_name, "ubiblock%d_%d", dev->ubi_num, dev->vol_id);
+	disk_capacity = (vi->size * vi->usable_leb_size) >> 9;
+	set_capacity(gd, disk_capacity);
+	dev->gd = gd;
+
+	spin_lock_init(&dev->queue_lock);
+	dev->rq = blk_init_queue(ubiblock_request, &dev->queue_lock);
+	if (!dev->rq) {
+		ubi_err("block: blk_init_queue failed");
+		ret = -ENODEV;
+		goto out_put_disk;
+	}
+
+	dev->rq->queuedata = dev;
+	dev->gd->queue = dev->rq;
+
+	/*
+	 * Create one workqueue per volume (per registered block device).
+	 * Rembember workqueues are cheap, they're not threads.
+	 */
+	dev->wq = alloc_workqueue(gd->disk_name, 0, 0);
+	if (!dev->wq)
+		goto out_free_queue;
+	INIT_WORK(&dev->work, ubiblock_do_work);
+
+	mutex_lock(&devices_mutex);
+	list_add_tail(&dev->list, &ubiblock_devices);
+	mutex_unlock(&devices_mutex);
+
+	/* Must be the last step: anyone can call file ops from now on */
+	add_disk(dev->gd);
+
+	ubi_msg("%s created from ubi%d:%d(%s)",
+		dev->gd->disk_name, dev->ubi_num, dev->vol_id, vi->name);
+
+	return 0;
+
+out_free_queue:
+	blk_cleanup_queue(dev->rq);
+out_put_disk:
+	put_disk(dev->gd);
+out_free_dev:
+	kfree(dev);
+
+	return ret;
+}
+
+static void ubiblock_cleanup(struct ubiblock *dev)
+{
+	del_gendisk(dev->gd);
+	blk_cleanup_queue(dev->rq);
+	ubi_msg("%s released", dev->gd->disk_name);
+	put_disk(dev->gd);
+}
+
+int ubiblock_del(struct ubi_volume_info *vi)
+{
+	struct ubiblock *dev;
+
+	mutex_lock(&devices_mutex);
+	dev = find_dev_nolock(vi->ubi_num, vi->vol_id);
+	if (!dev) {
+		mutex_unlock(&devices_mutex);
+		return -ENODEV;
+	}
+
+	/* Found a device, let's lock it so we can check if it's busy */
+	mutex_lock(&dev->dev_mutex);
+
+	if (dev->refcnt > 0) {
+		mutex_unlock(&dev->dev_mutex);
+		mutex_unlock(&devices_mutex);
+		return -EBUSY;
+	}
+
+	/* Remove from device list */
+	list_del(&dev->list);
+	mutex_unlock(&devices_mutex);
+
+	/* Flush pending work and stop this workqueue */
+	destroy_workqueue(dev->wq);
+
+	ubiblock_cleanup(dev);
+	mutex_unlock(&dev->dev_mutex);
+	kfree(dev);
+	return 0;
+}
+
+static void ubiblock_resize(struct ubi_volume_info *vi)
+{
+	struct ubiblock *dev;
+	int disk_capacity;
+
+	/*
+	 * Need to lock the device list until we stop using the device,
+	 * otherwise the device struct might get released in ubiblock_del().
+	 */
+	mutex_lock(&devices_mutex);
+	dev = find_dev_nolock(vi->ubi_num, vi->vol_id);
+	if (!dev) {
+		mutex_unlock(&devices_mutex);
+		return;
+	}
+
+	mutex_lock(&dev->dev_mutex);
+	disk_capacity = (vi->size * vi->usable_leb_size) >> 9;
+	set_capacity(dev->gd, disk_capacity);
+	ubi_msg("%s resized to %d LEBs", dev->gd->disk_name, vi->size);
+	mutex_unlock(&dev->dev_mutex);
+	mutex_unlock(&devices_mutex);
+}
+
+static int ubiblock_notify(struct notifier_block *nb,
+			 unsigned long notification_type, void *ns_ptr)
+{
+	struct ubi_notification *nt = ns_ptr;
+
+	switch (notification_type) {
+	case UBI_VOLUME_ADDED:
+		/*
+		 * We want to enforce explicit block device attaching for
+		 * volumes; so when a volume is added we do nothing.
+		 */
+		break;
+	case UBI_VOLUME_REMOVED:
+		ubiblock_del(&nt->vi);
+		break;
+	case UBI_VOLUME_RESIZED:
+		ubiblock_resize(&nt->vi);
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block ubiblock_notifier = {
+	.notifier_call = ubiblock_notify,
+};
+
+static struct ubi_volume_desc * __init
+open_volume_desc(const char *name, int ubi_num, int vol_id)
+{
+	if (ubi_num == -1)
+		/* No ubi num, name must be a vol device path */
+		return ubi_open_volume_path(name, UBI_READONLY);
+	else if (vol_id == -1)
+		/* No vol_id, must be vol_name */
+		return ubi_open_volume_nm(ubi_num, name, UBI_READONLY);
+	else
+		return ubi_open_volume(ubi_num, vol_id, UBI_READONLY);
+}
+
+static int __init ubiblock_attach_from_param(void)
+{
+	int i, ret;
+	struct ubiblock_param *p;
+	struct ubi_volume_desc *desc;
+	struct ubi_volume_info vi;
+
+	for (i = 0; i < ubiblock_devs; i++) {
+		p = &ubiblock_param[i];
+
+		desc = open_volume_desc(p->name, p->ubi_num, p->vol_id);
+		if (IS_ERR(desc)) {
+			ubi_err("block: can't open volume, err=%ld\n",
+				PTR_ERR(desc));
+			ret = PTR_ERR(desc);
+			break;
+		}
+
+		ubi_get_volume_info(desc, &vi);
+		ubi_close_volume(desc);
+
+		ret = ubiblock_add(&vi);
+		if (ret) {
+			ubi_err("block: can't add '%s' volume, err=%d\n",
+				vi.name, ret);
+			break;
+		}
+	}
+	return ret;
+}
+
+static void ubiblock_detach_all(void)
+{
+	struct ubiblock *next;
+	struct ubiblock *dev;
+
+	list_for_each_entry_safe(dev, next, &ubiblock_devices, list) {
+
+		/* Flush pending work and stop workqueue */
+		destroy_workqueue(dev->wq);
+
+		/* The module is being forcefully removed */
+		WARN_ON(dev->desc);
+
+		/* Remove from device list */
+		list_del(&dev->list);
+
+		ubiblock_cleanup(dev);
+
+		kfree(dev);
+	}
+}
+
+int __init ubiblock_init(void)
+{
+	int ret;
+
+	ubiblock_major = register_blkdev(0, "ubiblock");
+	if (ubiblock_major < 0)
+		return ubiblock_major;
+
+	/* Attach block devices from 'block=' module param */
+	ret = ubiblock_attach_from_param();
+	if (ret)
+		goto err_detach;
+
+	/*
+	 * Block devices needs to be attached to volumes explicitly
+	 * upon user request. So we ignore existing volumes.
+	 */
+	ret = ubi_register_volume_notifier(&ubiblock_notifier, 1);
+	if (ret)
+		goto err_unreg;
+	return 0;
+
+err_unreg:
+	unregister_blkdev(ubiblock_major, "ubiblock");
+err_detach:
+	ubiblock_detach_all();
+	return ret;
+}
+
+void __exit ubiblock_exit(void)
+{
+	ubi_unregister_volume_notifier(&ubiblock_notifier);
+
+	ubiblock_detach_all();
+
+	unregister_blkdev(ubiblock_major, "ubiblock");
+}
diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 57deae9..6e30a3c 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -1298,6 +1298,15 @@ static int __init ubi_init(void)
 		}
 	}
 
+	err = ubiblock_init();
+	if (err) {
+		ubi_err("block: cannot initialize, error %d", err);
+
+		/* See comment above re-ubi_is_module(). */
+		if (ubi_is_module())
+			goto out_detach;
+	}
+
 	return 0;
 
 out_detach:
@@ -1326,6 +1335,8 @@ static void __exit ubi_exit(void)
 {
 	int i;
 
+	ubiblock_exit();
+
 	for (i = 0; i < UBI_MAX_DEVICES; i++)
 		if (ubi_devices[i]) {
 			mutex_lock(&ubi_devices_mutex);
diff --git a/drivers/mtd/ubi/cdev.c b/drivers/mtd/ubi/cdev.c
index 8ca49f2..39d3774 100644
--- a/drivers/mtd/ubi/cdev.c
+++ b/drivers/mtd/ubi/cdev.c
@@ -561,6 +561,26 @@ static long vol_cdev_ioctl(struct file *file, unsigned int cmd,
 		break;
 	}
 
+	/* Attach a block device to an UBI volume */
+	case UBI_IOCVOLATTBLK:
+	{
+		struct ubi_volume_info vi;
+
+		ubi_get_volume_info(desc, &vi);
+		err = ubiblock_add(&vi);
+		break;
+	}
+
+	/* Dettach a block device from an UBI volume */
+	case UBI_IOCVOLDETBLK:
+	{
+		struct ubi_volume_info vi;
+
+		ubi_get_volume_info(desc, &vi);
+		err = ubiblock_del(&vi);
+		break;
+	}
+
 	default:
 		err = -ENOTTY;
 		break;
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index 8ea6297..e76ff98 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -864,6 +864,20 @@ int ubi_update_fastmap(struct ubi_device *ubi);
 int ubi_scan_fastmap(struct ubi_device *ubi, struct ubi_attach_info *ai,
 		     int fm_anchor);
 
+/* block.c */
+#ifdef CONFIG_MTD_UBI_BLOCK
+int ubiblock_init(void);
+void ubiblock_exit(void);
+int ubiblock_add(struct ubi_volume_info *vi);
+int ubiblock_del(struct ubi_volume_info *vi);
+#else
+static inline int ubiblock_init(void) { return 0; }
+static inline void ubiblock_exit(void) {}
+static inline int ubiblock_add(struct ubi_volume_info *vi) { return -ENOTTY; }
+static inline int ubiblock_del(struct ubi_volume_info *vi) { return -ENOTTY; }
+#endif
+
+
 /*
  * ubi_rb_for_each_entry - walk an RB-tree.
  * @rb: a pointer to type 'struct rb_node' to use as a loop counter
diff --git a/include/uapi/mtd/ubi-user.h b/include/uapi/mtd/ubi-user.h
index 723c324..b98585a 100644
--- a/include/uapi/mtd/ubi-user.h
+++ b/include/uapi/mtd/ubi-user.h
@@ -134,6 +134,13 @@
  * used. A pointer to a &struct ubi_set_vol_prop_req object is expected to be
  * passed. The object describes which property should be set, and to which value
  * it should be set.
+ *
+ * Block devices on UBI volumes
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * To attach or detach a block device from an UBI volume the %UBI_IOCVOLATTBLK
+ * and %UBI_IOCVOLDETBLK ioctl commands should be used, respectively.
+ * These commands take no arguments.
  */
 
 /*
@@ -191,6 +198,10 @@
 /* Set an UBI volume property */
 #define UBI_IOCSETVOLPROP _IOW(UBI_VOL_IOC_MAGIC, 6, \
 			       struct ubi_set_vol_prop_req)
+/* Attach a block device to an UBI volume */
+#define UBI_IOCVOLATTBLK _IO(UBI_VOL_IOC_MAGIC, 7)
+/* Detach a block device from an UBI volume */
+#define UBI_IOCVOLDETBLK _IO(UBI_VOL_IOC_MAGIC, 8)
 
 /* Maximum MTD device name length supported by UBI */
 #define MAX_UBI_MTD_NAME_LEN 127
-- 
1.8.1.5

Re: [PATCH v7 1/3] ubi: Introduce read-only block devices on top of UBI volumes

[Artem Bityutskiy]

On Mon, 2014-02-24 at 09:39 -0300, Ezequiel Garcia wrote:
> This commit introduces read-only block device emulation on top of UBI volumes.
> 
> Given UBI takes care of wear leveling and bad block management it's possible
> to add a thin layer to enable block device access to UBI volumes.
> This allows to use a block-oriented filesystem on a flash device.
> 
> The UBI block devices are meant to be used in conjunction with any
> regular, block-oriented file system (e.g. ext4), although it's primarily
> targeted at read-only file systems, such as squashfs.

Massaged a tiny bit and pushed to linux-ubifs.git, thanks!


-- 
Best Regards,
Artem Bityutskiy

Re: [PATCH v7 1/3] ubi: Introduce read-only block devices on top of UBI volumes

[Ezequiel Garcia]

On Fri, Feb 28, 2014 at 04:29:07PM +0200, Artem Bityutskiy wrote:
> On Mon, 2014-02-24 at 09:39 -0300, Ezequiel Garcia wrote:
> > This commit introduces read-only block device emulation on top of UBI volumes.
> > 
> > Given UBI takes care of wear leveling and bad block management it's possible
> > to add a thin layer to enable block device access to UBI volumes.
> > This allows to use a block-oriented filesystem on a flash device.
> > 
> > The UBI block devices are meant to be used in conjunction with any
> > regular, block-oriented file system (e.g. ext4), although it's primarily
> > targeted at read-only file systems, such as squashfs.
> 
> Massaged a tiny bit and pushed to linux-ubifs.git, thanks!
> 

Thanks for the massage!
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com

Re: [PATCH v7 3/3] Add UBI block interface documentation

[Artem Bityutskiy]

On Mon, 2014-02-24 at 09:39 -0300, Ezequiel Garcia wrote:
> Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
> ---
>  doc/general.xml |  4 ++++
>  doc/ubi.xml     | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  faq/ubi.xml     | 16 +++++++--------
>  3 files changed, 73 insertions(+), 8 deletions(-)

Pushed to mtd-www and then massaged a bit. I changed it so that it stops
using "attach" and "detach", but instead, uses "create" and "remove".

Thanks!

-- 
Best Regards,
Artem Bityutskiy

Re: [PATCH v7 2/3] ubi-utils: Add ubiblock tool

[Artem Bityutskiy]

Would it please be possible to use 'create' and 'remove' instead of
'attach' and 'detach'. I believe the whole thing will be less confusing
then, because these terms are already used for UBI<->MTD relations.

Also, would you please contribute this tool under GPLv2 license, rather
than GPL 2 or any later version. Because all the other UBI tools are
like this, it will make things simpler.

-- 
Best Regards,
Artem Bityutskiy

Re: [PATCH v7 2/3] ubi-utils: Add ubiblock tool

[Ezequiel Garcia]

On Tue, Mar 04, 2014 at 12:09:15PM +0200, Artem Bityutskiy wrote:
> Would it please be possible to use 'create' and 'remove' instead of
> 'attach' and 'detach'. I believe the whole thing will be less confusing
> then, because these terms are already used for UBI<->MTD relations.
> 

Sure, if you feel it's less confusing this way I have no problem.

> Also, would you please contribute this tool under GPLv2 license, rather
> than GPL 2 or any later version. Because all the other UBI tools are
> like this, it will make things simpler.
> 

Sure, no problem.
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com

Re: [PATCH v7 1/3] ubi: Introduce read-only block devices on top of UBI volumes

[Artem Bityutskiy]

On Mon, 2014-02-24 at 09:39 -0300, Ezequiel Garcia wrote:
> +/* Attach a block device to an UBI volume */
> +#define UBI_IOCVOLATTBLK _IO(UBI_VOL_IOC_MAGIC, 7)

Ezequiel,

please, change this before it goes upstream and instead, make the ioctls
accept a 'struct ubi_blkcreate_req' object pointer.

/**
 * blah
 * @padding1:  reserved for future, not used, has to be zeroed
 */
struct ubi_blkcreate_req {
	__s8 padding1[128];
} __packed;

This will make sure we have a possibility to extend this ioctl in the
future with something like volume creation flags etc. Otherwise, if we
need to add a flag, we'll have to introduce a new ioctl.

Thanks!

-- 
Best Regards,
Artem Bityutskiy

Re: [PATCH v7 1/3] ubi: Introduce read-only block devices on top of UBI volumes

[Ezequiel Garcia]

On Mar 05, Artem Bityutskiy wrote:
> On Mon, 2014-02-24 at 09:39 -0300, Ezequiel Garcia wrote:
> > +/* Attach a block device to an UBI volume */
> > +#define UBI_IOCVOLATTBLK _IO(UBI_VOL_IOC_MAGIC, 7)
> 
> Ezequiel,
> 
> please, change this before it goes upstream and instead, make the ioctls
> accept a 'struct ubi_blkcreate_req' object pointer.
> 
> /**
>  * blah
>  * @padding1:  reserved for future, not used, has to be zeroed
>  */
> struct ubi_blkcreate_req {
> 	__s8 padding1[128];
> } __packed;
> 
> This will make sure we have a possibility to extend this ioctl in the
> future with something like volume creation flags etc. Otherwise, if we
> need to add a flag, we'll have to introduce a new ioctl.
> 

Sure, that sounds great. And I'll change this ioctl names:

UBI_IOCBLKCR and UBI_IOCBLKRM ?

Unless you object.
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com

Re: [PATCH v7 1/3] ubi: Introduce read-only block devices on top of UBI volumes

[Artem Bityutskiy]

On Wed, 2014-03-05 at 09:52 -0300, Ezequiel Garcia wrote:
> Sure, that sounds great. And I'll change this ioctl names:
> 
> UBI_IOCBLKCR and UBI_IOCBLKRM ?

I actually did this, let me send the patch.

-- 
Best Regards,
Artem Bityutskiy