Embedded Linux development

* [PATCHv6] UBI: new module ubiblk: block layer on top of UBI
From: David Wagner @ 2011-09-22  7:58 UTC (permalink / raw)
  To: linux-mtd
  Cc: linux-embedded, lkml, Tim Bird, David Woodhouse, David Wagner,
	Artem Bityutskiy, Arnd Bergmann
In-Reply-To: <1308922482-14967-1-git-send-email-david.wagner@free-electrons.com>

ubiblk is a read-only block layer on top of UBI.  It presents UBI volumes as
read-only block devices (named ubiblkX_Y, where X is the UBI device number
and Y the Volume ID).

It is used by putting a block filesystem image on a UBI volume, creating the
corresponding ubiblk device and then mounting it.

It uses the UBI API to register to UBI notifications and to read from the
volumes.  It also creates a ubiblk_ctrl device node that simply receives ioctl
from a userspace tool for creating/removing ubiblk devices.

Some code is taken from mtd_blkdevs and gluebi.  Some code for the ioctl part is
also inspired from ubi's core.

Advantages of ubiblk over gluebi+mtdblock_ro:

 * Simpler architecture

 * The numbering of devices is much easier with ubiblk than with
   gluebi+mtdblock_ro. With gluebi+mtdblock_ro, you get one additional MTD
   device for each UBI volume, so the number of MTD devices grows quite a lot
   and is a bit difficult to understand. For example, mtdblock[0-4] might be
   your real MTD partitions, while mtdblock[5-9] might be your UBI volumes.
   It also means that if a new real MTD partition is added, the index of all the
   MTD devices exposing UBI volumes will be shifted by one, which is a bit
   confusing/annoying.
   As well, if you add an UBI volume, the mtdblock devices that are emulated on
   top of volumes that come after this new one will have their ID incremented.

 * ubiblk devices are created on a 'on-demand' basis, which avoids wasting
   resources.

 * It is also possible to specify a "volume" parameter in order to create a
   ubiblk device at init time.  This makes possible to put a rootfs on a ubiblk
   device.

 * The performance appears to be slightly better with ubiblk than
   gluebi+mtdblock_ro, according to our benchmarks (see
   http://elinux.org/Flash_Filesystem_Benchmarks_2.6.39)

Signed-off-by: David Wagner <david.wagner@free-electrons.com>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
---

	changelog since v5:
	~~~~~~~~~~~~~~~~~~~

 * Use list_for_each_entry instead of list_for_each

 * Add a "volume" parameter for creating a device at init time.  It allows to
   put a rootfs on the volume.  Format: volume=<ubi_num>:<vol_id>

 * Locking: remove useless locks and add necessary new locks

 * Remove the CONFIG_COMPAT code

 * Don't walk the error path if register_blkdev returns 0

 * WARN when a ubiblk device still has an open descriptor at exit time (happens
   with rmmod -f).

 * Use temporary variables for readability

 * Add dynamic debug regarding refcounting

 * Remove a useless check in ubiblk_create (the test consisted in opening the
   proxified volume)

 * In ubiblk_create(), directly use vi (passed as argument) instead of dev->vi

 * No need to remove the devices from the linked list at exit time: it doesn't
   free any memory

 * Add padding in the ioctl data structure

 * remove a useless kfree(dev->vi) in ubiblk_remove: the refcounting assures
   that it has been freed before (in ubiblk_release).  Same in exit.


	@Artem regarding ubiblk_release:
it is only called when the device is closed (eg, unmounted), not when it is
removed (eg the volume disappears or the user send an ioctl to remove it).  The
function responsible for removing a device (and thus removing it from the linked
list) is ubiblk_remove.

 Documentation/ioctl/ioctl-number.txt |    1 +
 drivers/mtd/ubi/Kconfig              |   16 +
 drivers/mtd/ubi/Makefile             |    1 +
 drivers/mtd/ubi/ubiblk.c             |  751 ++++++++++++++++++++++++++++++++++
 include/mtd/Kbuild                   |    1 +
 include/mtd/ubiblk-user.h            |   49 +++
 6 files changed, 819 insertions(+), 0 deletions(-)
 create mode 100644 drivers/mtd/ubi/ubiblk.c
 create mode 100644 include/mtd/ubiblk-user.h

diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index 845a191..b24df7f 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -150,6 +150,7 @@ Code  Seq#(hex)	Include File		Comments
 'M'	00-0F	drivers/video/fsl-diu-fb.h	conflict!
 'N'	00-1F	drivers/usb/scanner.h
 'O'     00-06   mtd/ubi-user.h		UBI
+'O'     10-11   mtd/ubiblk-user.h       ubiblk
 'P'	all	linux/soundcard.h	conflict!
 'P'	60-6F	sound/sscape_ioctl.h	conflict!
 'P'	00-0F	drivers/usb/class/usblp.c	conflict!
diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index 4dcc752..977934a 100644
--- a/drivers/mtd/ubi/Kconfig
+++ b/drivers/mtd/ubi/Kconfig
@@ -60,4 +60,20 @@ config MTD_UBI_DEBUG
 	help
 	  This option enables UBI debugging.
 
+config MTD_UBI_UBIBLK
+	tristate "Read-only block transition layer on top of UBI"
+	help
+	   Read-only block interface on top of UBI.
+
+	   This option adds ubiblk, which creates a read-ony block device from
+	   UBI volumes.  It makes it possible to use R/O block filesystems on
+	   top of UBI volumes (and hence, on top of MTDs while avoiding bad
+	   blocks).
+
+	   ubiblk devices are created by invoking appropriate ioctl to the
+	   ubiblk_ctrl device node.
+
+	   The devices are named ubiblkX_Y where X is the UBI number and Y is
+	   the Volume ID.
+
 endif # MTD_UBI
diff --git a/drivers/mtd/ubi/Makefile b/drivers/mtd/ubi/Makefile
index c9302a5..354b2df 100644
--- a/drivers/mtd/ubi/Makefile
+++ b/drivers/mtd/ubi/Makefile
@@ -5,3 +5,4 @@ ubi-y += misc.o
 
 ubi-$(CONFIG_MTD_UBI_DEBUG) += debug.o
 obj-$(CONFIG_MTD_UBI_GLUEBI) += gluebi.o
+obj-$(CONFIG_MTD_UBI_UBIBLK) += ubiblk.o
diff --git a/drivers/mtd/ubi/ubiblk.c b/drivers/mtd/ubi/ubiblk.c
new file mode 100644
index 0000000..d22ae4f
--- /dev/null
+++ b/drivers/mtd/ubi/ubiblk.c
@@ -0,0 +1,751 @@
+/*
+ * Copyright (c) Free Electrons, 2011
+ * Copyright (c) International Business Machines Corp., 2006
+ * Copyright © 2003-2010 David Woodhouse <dwmw2@infradead.org>
+ *
+ * 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+ * Author: David Wagner
+ * Some code taken from gluebi.c
+ *	(Artem Bityutskiy (Битюцкий Артём), Joern Engel)
+ * Some code taken from cdev.c (Artem Bityutskiy (Битюцкий Артём))
+ * Some code taken from mtd_blkdevs.c (David Woodhouse)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/vmalloc.h>
+#include <linux/mtd/ubi.h>
+#include <linux/blkdev.h>
+#include <linux/miscdevice.h>
+#include <linux/kthread.h>
+#include <linux/mutex.h>
+#include <linux/list.h>
+#include <mtd/ubiblk-user.h>
+#include "ubi.h"
+
+#define BLK_SIZE 512
+
+/**
+ * struct ubiblk_dev - represents a ubiblk device, proxying a UBI volume
+ * @desc: open UBI volume descriptor
+ * @vi: UBI volume information
+ * @ubi_num: UBI device number
+ * @vol_id: UBI volume identifier
+ * @refcnt: reference counter (increases with open(), decreases with release())
+ * @gd: the disk (block device) created by ubiblk
+ * @rq: the request queue to @gd
+ * @req_task: the thread processing @rq requests
+ * @vol_lock: protects write access to the elements of this structure
+ * @queue_lock: avoids concurrent accesses to the request queue
+ * @list: linked list structure
+ */
+struct ubiblk_dev {
+	struct ubi_volume_desc *desc;
+	struct ubi_volume_info *vi;
+	int ubi_num;
+	int vol_id;
+	int refcnt;
+
+	struct gendisk *gd;
+	struct request_queue *rq;
+	struct task_struct *req_task;
+
+	struct mutex vol_lock;
+
+	spinlock_t queue_lock;
+
+	struct list_head list;
+};
+
+/* Linked list of all ubiblk_dev instances */
+static LIST_HEAD(ubiblk_devs);
+
+/* Avoid concurrent access to the above list */
+static DEFINE_MUTEX(devlist_lock);
+
+static int ubiblk_major;
+static const struct block_device_operations ubiblk_ops;
+
+/* The device receiving the ioctls */
+static struct miscdevice ctrl_dev;
+
+#define VOL_PARAM_MAXLEN 8
+static char *volume;
+module_param(volume, charp, 0000);
+MODULE_PARM_DESC(volume,
+	"Format: volume=<ubi_num>:<vol_id>\n"
+	"Create a ubiblk device at init time.  Useful for mounting it as root "
+	"device.");
+
+static struct ubiblk_dev *ubiblk_find_dev(struct ubi_volume_info *vi)
+{
+	struct ubiblk_dev *dev;
+
+	list_for_each_entry(dev, &ubiblk_devs, list) {
+		if (dev && dev->ubi_num == vi->ubi_num &&
+		    dev->vol_id == vi->vol_id)
+			return dev;
+	}
+	return NULL;
+}
+
+/**
+ * do_ubiblk_request - Read a LEB and fill the request buffer with the
+ * requested sector
+ *
+ * @req: the request data structure
+ * @dev: the ubiblk device on which the request is issued
+ */
+static int do_ubiblk_request(struct request *req, struct ubiblk_dev *dev)
+{
+	unsigned long start, len, read_bytes;
+	int offset;
+	int leb;
+	int ret;
+
+	start = blk_rq_pos(req) << 9;
+	len = blk_rq_cur_bytes(req);
+	read_bytes = 0;
+
+	/* We are always reading. No need to handle writing for now */
+
+	leb = start / dev->vi->usable_leb_size;
+	offset = start % dev->vi->usable_leb_size;
+
+	do {
+		if (offset + len > dev->vi->usable_leb_size)
+			len = dev->vi->usable_leb_size - offset;
+
+		if (unlikely(blk_rq_pos(req) + blk_rq_cur_sectors(req) >
+		    get_capacity(req->rq_disk))) {
+			dev_err(disk_to_dev(dev->gd),
+				"attempting to read too far\n");
+			return -EIO;
+		}
+
+		/* Read (len) bytes of LEB (leb) from (offset) and put the
+		 * result in the buffer given by the request.
+		 * If the request is overlapping on several lebs, (read_bytes)
+		 * will be > 0 and the data will be put in the buffer at
+		 * offset (read_bytes)
+		 */
+		ret = ubi_read(dev->desc, leb, req->buffer + read_bytes,
+			       offset, len);
+
+		if (ret) {
+			dev_err(disk_to_dev(dev->gd), "ubi_read error\n");
+			return ret;
+		}
+
+		read_bytes += len;
+
+		len = blk_rq_cur_bytes(req) - read_bytes;
+		leb++;
+		offset = 0;
+	} while (read_bytes < blk_rq_cur_bytes(req));
+
+	return 0;
+}
+
+/**
+ * ubi_ubiblk_request - wakes the processing thread
+ *
+ * @rq: the request queue which device is to be awaken
+ */
+static void ubi_ubiblk_request(struct request_queue *rq)
+{
+	struct ubiblk_dev *dev;
+	struct request *req = NULL;
+
+	dev = rq->queuedata;
+
+	if (!dev)
+		while ((req = blk_fetch_request(rq)) != NULL)
+			__blk_end_request_all(req, -ENODEV);
+	else
+		wake_up_process(dev->req_task);
+}
+
+/**
+ * ubiblk_open - open a UBI volume (get the volume descriptor)
+ *
+ * @bdev: the corresponding block device
+ * @mode: opening mode (don't care as long as ubiblk is read-only)
+ */
+static int ubiblk_open(struct block_device *bdev, fmode_t mode)
+{
+	struct ubiblk_dev *dev = bdev->bd_disk->private_data;
+	int err = 0;
+
+	mutex_lock(&dev->vol_lock);
+	dev_dbg(disk_to_dev(dev->gd), "open(); refcnt = %d\n", dev->refcnt);
+	if (dev->refcnt > 0) {
+		/*
+		 * The volume is already opened ; just increase the reference
+		 * counter.
+		 */
+		dev->refcnt++;
+		mutex_unlock(&dev->vol_lock);
+		return 0;
+	}
+
+	dev->desc = ubi_open_volume(dev->ubi_num, dev->vol_id,
+					UBI_READONLY);
+	if (IS_ERR(dev->desc)) {
+		dev_err(disk_to_dev(dev->gd), "failed to open");
+
+		err = PTR_ERR(dev->desc);
+		dev->desc = NULL;
+		goto out_lock;
+	}
+
+	dev->vi = kzalloc(sizeof(struct ubi_volume_info), GFP_KERNEL);
+	if (!dev->vi) {
+		err = -ENOMEM;
+		goto out_close;
+	}
+	ubi_get_volume_info(dev->desc, dev->vi);
+
+	dev->refcnt++;
+	dev_dbg(disk_to_dev(dev->gd), "opened mode=%d\n", mode);
+	mutex_unlock(&dev->vol_lock);
+	return 0;
+
+out_close:
+	ubi_close_volume(dev->desc);
+	dev->desc = NULL;
+out_lock:
+	mutex_unlock(&dev->vol_lock);
+	return err;
+}
+
+/**
+ * ubiblk_release - close a UBI volume (close the volume descriptor)
+ *
+ * @gd: the disk that was previously opened
+ * @mode: don't care
+ */
+static int ubiblk_release(struct gendisk *gd, fmode_t mode)
+{
+	struct ubiblk_dev *dev = gd->private_data;
+
+	mutex_lock(&dev->vol_lock);
+	dev_dbg(disk_to_dev(dev->gd), "release(); refcnt = %d\n", dev->refcnt);
+
+	dev->refcnt--;
+	if (dev->refcnt == 0) {
+		kfree(dev->vi);
+		dev->vi = NULL;
+
+		ubi_close_volume(dev->desc);
+		dev->desc = NULL;
+
+		dev_dbg(disk_to_dev(dev->gd), "released, mode=%d\n", mode);
+	}
+
+	mutex_unlock(&dev->vol_lock);
+	return 0;
+}
+
+/**
+ * ubi_ubiblk_thread - loop on the block request queue and wait for new
+ * requests ; run them with do_ubiblk_request(). Mostly copied from
+ * mtd_blkdevs.c
+ *
+ * @arg: the ubiblk device which request queue to process
+ */
+static int ubi_ubiblk_thread(void *arg)
+{
+	struct ubiblk_dev *dev = arg;
+	struct request_queue *rq = dev->rq;
+	struct request *req = NULL;
+
+	spin_lock_irq(rq->queue_lock);
+
+	while (!kthread_should_stop()) {
+		int res;
+
+		if (!req)
+			req = blk_fetch_request(rq);
+		if (!req) {
+			set_current_state(TASK_INTERRUPTIBLE);
+
+			if (kthread_should_stop())
+				set_current_state(TASK_RUNNING);
+
+			spin_unlock_irq(rq->queue_lock);
+			schedule();
+			spin_lock_irq(rq->queue_lock);
+			continue;
+		}
+
+		spin_unlock_irq(rq->queue_lock);
+
+		mutex_lock(&dev->vol_lock);
+		res = do_ubiblk_request(req, dev);
+		mutex_unlock(&dev->vol_lock);
+
+		spin_lock_irq(rq->queue_lock);
+
+		if (!__blk_end_request_cur(req, res))
+			req = NULL;
+	}
+
+	if (req)
+		__blk_end_request_all(req, -EIO);
+
+	spin_unlock_irq(rq->queue_lock);
+
+	return 0;
+}
+
+/**
+ * ubiblk_create - create a ubiblk device proxying a UBI volume
+ *
+ * @vi: the UBI volume information data structure
+ *
+ * An UBI volume has been created ; create a corresponding ubiblk device:
+ * Initialize the locks, the structure, the block layer infos and start a
+ * req_task.
+ */
+static int ubiblk_create(struct ubi_volume_info *vi)
+{
+	struct ubiblk_dev *dev;
+	struct gendisk *gd;
+	int disk_capacity;
+	int ret = 0;
+
+	mutex_lock(&devlist_lock);
+	/* Check that the volume isn't already proxyfied */
+	if (ubiblk_find_dev(vi)) {
+		ret = -EEXIST;
+		goto out_lock;
+	}
+
+	dev = kzalloc(sizeof(struct ubiblk_dev), GFP_KERNEL);
+	if (!dev) {
+		ret = -ENOMEM;
+		goto out_lock;
+	}
+
+	mutex_init(&dev->vol_lock);
+
+	dev->ubi_num = vi->ubi_num;
+	dev->vol_id = vi->vol_id;
+
+	/* Initialize the gendisk of this ubiblk device */
+	gd = alloc_disk(1);
+	if (!gd) {
+		pr_err("alloc_disk failed\n");
+		ret = -ENODEV;
+		goto out_lock;
+	}
+
+	gd->fops = &ubiblk_ops;
+	gd->major = ubiblk_major;
+	gd->first_minor = dev->ubi_num * UBI_MAX_VOLUMES + dev->vol_id;
+	gd->private_data = dev;
+	sprintf(gd->disk_name, "ubiblk%d_%d", dev->ubi_num, dev->vol_id);
+	disk_capacity = (vi->size * vi->usable_leb_size) >> 9;
+	set_capacity(gd, disk_capacity);
+	set_disk_ro(gd, 1);
+	dev->gd = gd;
+
+	spin_lock_init(&dev->queue_lock);
+	dev->rq = blk_init_queue(ubi_ubiblk_request, &dev->queue_lock);
+	if (!dev->rq) {
+		pr_err("blk_init_queue failed\n");
+		ret = -ENODEV;
+		goto out_queue;
+	}
+	dev->rq->queuedata = dev;
+	blk_queue_logical_block_size(dev->rq, BLK_SIZE);
+	dev->gd->queue = dev->rq;
+
+	/* Borrowed from mtd_blkdevs.c */
+	/* Create processing req_task
+	 *
+	 * The processing of the request has to be done in process context (it
+	 * might sleep) but blk_run_queue can't block ; so we need to separate
+	 * the event of a request being added to the queue (which triggers the
+	 * callback ubi_ubiblk_request - that is set with blk_init_queue())
+	 * and the processing of that request.
+	 *
+	 * Thus, the sole purpose of ubi_ubiblk_reuqest is to wake the kthread
+	 * up so that it will process the request queue
+	 */
+	dev->req_task = kthread_run(ubi_ubiblk_thread, dev, "%s%d_%d",
+				  "kubiblk", dev->ubi_num, dev->vol_id);
+	if (IS_ERR(dev->req_task)) {
+		ret = PTR_ERR(dev->req_task);
+		goto out_thread;
+	}
+
+	list_add(&dev->list, &ubiblk_devs);
+	add_disk(dev->gd);
+
+	dev_info(disk_to_dev(dev->gd),
+		 "created from ubi%d:%d(%s)\n", dev->ubi_num, dev->vol_id,
+		 vi->name);
+
+	mutex_unlock(&devlist_lock);
+
+	return 0;
+
+out_thread:
+	blk_cleanup_queue(dev->rq);
+out_queue:
+	put_disk(dev->gd);
+out_lock:
+	mutex_unlock(&devlist_lock);
+
+	return ret;
+}
+
+/**
+ * ubiblk_remove - destroy a ubiblk device
+ *
+ * @vi: the UBI volume information data structure
+ *
+ * A UBI volume has been removed or we are requested to unproxify a volume ;
+ * destroy the corresponding ubiblk device
+ */
+static int ubiblk_remove(struct ubi_volume_info *vi)
+{
+	struct ubiblk_dev *dev = NULL;
+
+	mutex_lock(&devlist_lock);
+
+	dev = ubiblk_find_dev(vi);
+
+	if (!dev) {
+		mutex_unlock(&devlist_lock);
+		pr_warn("trying to remove %s, but it isn't handled\n",
+			vi->name);
+		return -ENODEV;
+	}
+
+	mutex_lock(&dev->vol_lock);
+	if (dev->desc) {
+		mutex_unlock(&dev->vol_lock);
+		mutex_unlock(&devlist_lock);
+		return -EBUSY;
+	}
+
+	del_gendisk(dev->gd);
+	blk_cleanup_queue(dev->rq);
+	kthread_stop(dev->req_task);
+	put_disk(dev->gd);
+
+	list_del(&dev->list);
+	mutex_unlock(&dev->vol_lock);
+	mutex_unlock(&devlist_lock);
+
+	kfree(dev);
+	pr_info("unproxyfied %s\n", vi->name);
+	return 0;
+}
+
+/**
+ * ubiblk_resize - resize a ubiblk device
+ *
+ * @vi: the UBI volume information data structure
+ *
+ * A UBI volume has been resized, change the ubiblk device geometry accordingly
+ */
+static int ubiblk_resize(struct ubi_volume_info *vi)
+{
+	struct ubiblk_dev *dev;
+	int disk_capacity;
+
+	/* We don't touch the list, but we better lock it: it could be that the
+	 * device gets removed between the time the device has been found and
+	 * the time we access dev->gd
+	 */
+	mutex_lock(&devlist_lock);
+	dev = ubiblk_find_dev(vi);
+	if (!dev) {
+		mutex_unlock(&devlist_lock);
+		pr_warn("trying to resize %s, which isn't handled\n",
+			vi->name);
+		return -ENODEV;
+	}
+
+	mutex_lock(&dev->vol_lock);
+	disk_capacity = (vi->size * vi->usable_leb_size) >> 9;
+	set_capacity(dev->gd, disk_capacity);
+	dev_dbg(disk_to_dev(dev->gd), "resized to %d LEBs\n", vi->size);
+	mutex_unlock(&dev->vol_lock);
+
+	mutex_unlock(&devlist_lock);
+	return 0;
+}
+
+/**
+ * ubiblk_notify - dispatches the UBI notifications
+ * copied from gluebi.c
+ *
+ * @nb: unused
+ * @notification_type: the notification type sent by UBI
+ * @ns_ptr: contains the notifications' additional informations
+ */
+static int ubiblk_notify(struct notifier_block *nb,
+			 unsigned long notification_type, void *ns_ptr)
+{
+	struct ubi_notification *nt = ns_ptr;
+
+	switch (notification_type) {
+	case UBI_VOLUME_REMOVED:
+		ubiblk_remove(&nt->vi);
+		break;
+	case UBI_VOLUME_RESIZED:
+		ubiblk_resize(&nt->vi);
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+static const struct block_device_operations ubiblk_ops = {
+	.owner = THIS_MODULE,
+	.open = ubiblk_open,
+	.release = ubiblk_release,
+};
+
+static struct notifier_block ubiblk_notifier = {
+	.notifier_call = ubiblk_notify,
+};
+
+
+/**
+ * ubiblk_ctrl_ioctl - ioctl handling for proxying/unproxying a UBI volume
+ *
+ * @file: the file on which the ioctl was invoked (usunsed)
+ * @cmd: the ioctl type
+ * @arg: additional command informations
+ */
+static long ubiblk_ctrl_ioctl(struct file *file, unsigned int cmd,
+			      unsigned long arg)
+{
+	int err = 0;
+	void __user *argp = (void __user *)arg;
+
+	struct ubi_volume_desc *desc;
+	struct ubi_volume_info vi;
+	struct ubiblk_ctrl_req req;
+
+	if (!capable(CAP_SYS_RESOURCE))
+		return -EPERM;
+
+	err = copy_from_user(&req, argp, sizeof(struct ubiblk_ctrl_req));
+	if (err)
+		return -EFAULT;
+
+	if (req.ubi_num < 0 || req.vol_id < 0)
+		return -EINVAL;
+
+	desc = ubi_open_volume(req.ubi_num, req.vol_id, UBI_READONLY);
+	if (IS_ERR(desc)) {
+		dev_err(ctrl_dev.this_device, "opening ubi%d:%d failed\n",
+			req.ubi_num, req.vol_id);
+		return PTR_ERR(desc);
+	}
+
+	ubi_get_volume_info(desc, &vi);
+
+	switch (cmd) {
+	case UBIBLK_IOCADD:
+		dev_info(ctrl_dev.this_device, "proxying ubi%d:%d\n",
+			 req.ubi_num, req.vol_id);
+		err = ubiblk_create(&vi);
+		break;
+	case UBIBLK_IOCDEL:
+		dev_info(ctrl_dev.this_device, "unproxying ubi%d:%d\n",
+			 req.ubi_num, req.vol_id);
+		err = ubiblk_remove(&vi);
+		break;
+
+	default:
+		err = -ENOTTY;
+		break;
+	}
+
+	ubi_close_volume(desc);
+
+	return err;
+}
+
+/* ubiblk control device (receives ioctls) */
+static const struct file_operations ubiblk_ctrl_ops = {
+	.owner = THIS_MODULE,
+	.unlocked_ioctl = ubiblk_ctrl_ioctl,
+	.llseek = no_llseek,
+};
+static struct miscdevice ctrl_dev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "ubiblk_ctrl",
+	.fops = &ubiblk_ctrl_ops,
+};
+
+/**
+ * ubiblk_parse_volume_param - parse the "volume" module parameter
+ *
+ * @ubi_num: where to store the UBI device number
+ * @vol_id: where to store the volume ID
+ */
+static int __init ubiblk_parse_volume_param(int *ubi_num, int *vol_id)
+{
+	char *tokens[2] = {NULL, NULL};
+	char buf[VOL_PARAM_MAXLEN];
+	char *pbuf = buf;
+	int len = strlen(buf);
+	int err;
+
+	if (len > VOL_PARAM_MAXLEN || len == 0)
+		return -1;
+
+	strcpy(buf, volume);
+	tokens[0] = strsep(&pbuf, ":");
+	tokens[1] = strsep(&pbuf, ":");
+
+	if (pbuf)
+		return -1; /* There are surnumerous parameters */
+
+	err = kstrtoint(tokens[0], 10, ubi_num);
+	if (err < 0 || *ubi_num < 0)
+		return -1;
+
+	err = kstrtoint(tokens[1], 10, vol_id);
+	if (err < 0 || *vol_id < 0)
+		return -1;
+
+	return 0;
+}
+
+/**
+ * ubiblk_inittime_volume - create a volume at init time
+ *
+ * If the user passed a "ubiblk.volume" argument, check it and create the said
+ * volume.
+ */
+static void __init ubiblk_inittime_volume(void)
+{
+	int ubi_num, vol_id;
+	int err;
+	struct ubi_volume_desc *desc;
+	struct ubi_volume_info vi;
+
+	if (ubiblk_parse_volume_param(&ubi_num, &vol_id) < 0) {
+		pr_err("cannot parse the volume parameter");
+		return;
+	}
+
+	desc = ubi_open_volume(ubi_num, vol_id, UBI_READONLY);
+	if (IS_ERR(desc)) {
+		pr_err("opening ubi%d:%d failed: %ld\n", ubi_num, vol_id,
+		       PTR_ERR(desc));
+		return;
+	}
+	ubi_get_volume_info(desc, &vi);
+
+	err = ubiblk_create(&vi);
+	if (err < 0) {
+		pr_err("can't create the initial device "
+		       "ubiblk%d_%d: %d\n", ubi_num, vol_id, err);
+	}
+	ubi_close_volume(desc);
+}
+
+/**
+ * ubi_ubiblk_init - initialize the module
+ *
+ * Get a major number and register to UBI notifications ; register the ioctl
+ * handler device
+ */
+static int __init ubi_ubiblk_init(void)
+{
+	int ret = 0;
+
+	ret = register_blkdev(0, "ubiblk");
+	if (ret < 0)
+		return ret;
+	ubiblk_major = ret;
+
+	/* Check if the user wants a volume to be proxified at init time */
+	if (volume)
+		ubiblk_inittime_volume();
+
+	ret = ubi_register_volume_notifier(&ubiblk_notifier, 1);
+	if (ret < 0)
+		goto out_unreg_blk;
+
+	ret = misc_register(&ctrl_dev);
+	if (ret) {
+		pr_err("can't register control device\n");
+		goto out_unreg_notifier;
+	}
+
+	pr_info("major device number is %d\n", ubiblk_major);
+
+	return ret;
+
+out_unreg_notifier:
+	ubi_unregister_volume_notifier(&ubiblk_notifier);
+out_unreg_blk:
+	unregister_blkdev(ubiblk_major, "ubiblk");
+
+	return ret;
+}
+
+/**
+ * ubi_ubiblk_exit - end of life
+ *
+ * unregister the block device major, unregister from UBI notifications,
+ * unregister the ioctl handler device stop the threads and free the memory.
+ */
+static void __exit ubi_ubiblk_exit(void)
+{
+	struct ubiblk_dev *next;
+	struct ubiblk_dev *dev;
+
+	ubi_unregister_volume_notifier(&ubiblk_notifier);
+	misc_deregister(&ctrl_dev);
+
+	list_for_each_entry_safe(dev, next, &ubiblk_devs, list) {
+		/* The module is being forcefully removed */
+		WARN_ON(dev->desc);
+
+		del_gendisk(dev->gd);
+		blk_cleanup_queue(dev->rq);
+		kthread_stop(dev->req_task);
+		put_disk(dev->gd);
+
+		kfree(dev);
+	}
+
+	unregister_blkdev(ubiblk_major, "ubiblk");
+}
+
+module_init(ubi_ubiblk_init);
+module_exit(ubi_ubiblk_exit);
+MODULE_DESCRIPTION("Read-only block transition layer on top of UBI");
+MODULE_AUTHOR("David Wagner");
+MODULE_LICENSE("GPL");
diff --git a/include/mtd/Kbuild b/include/mtd/Kbuild
index 192f8fb..d0d59d8 100644
--- a/include/mtd/Kbuild
+++ b/include/mtd/Kbuild
@@ -3,3 +3,4 @@ header-y += mtd-abi.h
 header-y += mtd-user.h
 header-y += nftl-user.h
 header-y += ubi-user.h
+header-y += ubiblk-user.h
diff --git a/include/mtd/ubiblk-user.h b/include/mtd/ubiblk-user.h
new file mode 100644
index 0000000..96858c7
--- /dev/null
+++ b/include/mtd/ubiblk-user.h
@@ -0,0 +1,49 @@
+/*
+ * Copyright © Free Electrons, 2011
+ * Copyright © International Business Machines Corp., 2006
+ *
+ * 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+ * Author: David Wagner
+ * Some code taken from ubi-user.h
+ */
+
+#ifndef __UBIBLK_USER_H__
+#define __UBIBLK_USER_H__
+
+#include <linux/types.h>
+
+/**
+ * ubiblk_ctrl_req - additional ioctl data structure
+ * @ubi_num: UBI device number
+ * @vol_id: UBI volume identifier
+ * @padding: reserved for future, must contain zeroes
+ */
+struct ubiblk_ctrl_req {
+	__s32 ubi_num;
+	__s32 vol_id;
+	__u8 padding[8];
+} __packed;
+
+/* ioctl commands of the UBI control character device */
+#define UBIBLK_CTRL_IOC_MAGIC 'O'
+
+/* Create a ubiblk device from a UBI volume */
+#define UBIBLK_IOCADD _IOW(UBIBLK_CTRL_IOC_MAGIC, 0x10, struct ubiblk_ctrl_req)
+/* Delete a ubiblk device */
+#define UBIBLK_IOCDEL _IOW(UBIBLK_CTRL_IOC_MAGIC, 0x11, struct ubiblk_ctrl_req)
+/* If you add ioctls here, please note that UBI uses 'O'/0x00-0x06 */
+
+#endif
-- 
1.7.0.4

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