Message-Id: <1315821061-14819-1-git-send-email-david.wagner@free-electrons.com>
Date:	Mon, 12 Sep 2011 11:51:01 +0200
From:	David Wagner <david.wagner@...e-electrons.com>
To:	linux-mtd <linux-mtd@...ts.infradead.org>
Cc:	Artem Bityutskiy <dedekind1@...il.com>,
	linux-embedded <linux-embedded@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Tim Bird <tim.bird@...sony.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	David Wagner <david.wagner@...e-electrons.com>
Subject: [PATCHv5] UBI: new module ubiblk: block layer on top of UBI

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.

 * 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@...e-electrons.com>
---

changes since v4:
~~~~~~~~~~~~~~~~~

 * Add missing headers (they are included by other headers but it seems to be
   good practice not to rely on that).

 * Remove an macro rendered useless with the linked lists

 * correct some formatting in kerneldoc comments

 * introduce refcounting to avoid multiple opens or closing a UBI volume while
   still in use

 * make checkpatch happy about assignation inside a condition

 * use DEFINE_MUTEX for devlist_lock

plan for v6:
~~~~~~~~~~~~

 * Use list_for_each_entry

 * Dig into Arnd's suggestions, understand it and see if/how it could be done

 * If it isn't rendered obsolete by the previous point, add a kernel parameter
   for creating ubiblk devices at boot time (in order to have a rootfs on a
   ubiblk device)

 Documentation/ioctl/ioctl-number.txt |    1 +
 drivers/mtd/ubi/Kconfig              |   16 +
 drivers/mtd/ubi/Makefile             |    1 +
 drivers/mtd/ubi/ubiblk.c             |  724 ++++++++++++++++++++++++++++++++++
 include/mtd/Kbuild                   |    1 +
 include/mtd/ubiblk-user.h            |   47 +++
 6 files changed, 790 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..6abf76b
--- /dev/null
+++ b/drivers/mtd/ubi/ubiblk.c
@@ -0,0 +1,724 @@
+/*
+ * Copyright (c) Free Electrons, 2011
+ * Copyright (c) International Business Machines Corp., 2006
+ * Copyright © 2003-2010 David Woodhouse <dwmw2@...radead.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;
+
+static struct ubiblk_dev *ubiblk_find_dev(struct ubi_volume_info *vi)
+{
+	struct ubiblk_dev *dev;
+	struct list_head *list_ptr;
+
+	/* TODO: use list_for_each_entry ? */
+	list_for_each(list_ptr, &ubiblk_devs) {
+		dev = list_entry(list_ptr, struct ubiblk_dev, list);
+		if (dev && dev->ubi_num == vi->ubi_num &&
+		    dev->vol_id == vi->vol_id)
+			break;
+		dev = NULL;
+	}
+	return dev;
+}
+
+/**
+ * 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);
+	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->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 ret = 0;
+
+	mutex_lock(&devlist_lock);
+	/* Check that the volume isn't already proxyfied */
+	if (ubiblk_find_dev(vi)) {
+		ret = -EEXIST;
+		goto out_devlist;
+	}
+
+	dev = kzalloc(sizeof(struct ubiblk_dev), GFP_KERNEL);
+	if (!dev) {
+		ret = -ENOMEM;
+		goto out_devlist;
+	}
+
+	list_add(&dev->list, &ubiblk_devs);
+
+	mutex_init(&dev->vol_lock);
+	mutex_lock(&dev->vol_lock);
+
+	dev->ubi_num = vi->ubi_num;
+	dev->vol_id = vi->vol_id;
+
+	dev->desc = ubi_open_volume(dev->ubi_num, dev->vol_id,
+					UBI_READONLY);
+	if (IS_ERR(dev->desc)) {
+		pr_err("ubi_open_volume failed\n");
+		ret = PTR_ERR(dev->desc);
+		goto out_vol;
+	}
+
+	dev->vi = kzalloc(sizeof(struct ubi_volume_info), GFP_KERNEL);
+	if (!dev->vi) {
+		ret = -ENOMEM;
+		goto out_info;
+	}
+	ubi_get_volume_info(dev->desc, dev->vi);
+
+	/* Initialize the gendisk of this ubiblk device */
+	gd = alloc_disk(1);
+	if (!gd) {
+		pr_err("alloc_disk failed\n");
+		ret = -ENODEV;
+		goto out_disk;
+	}
+
+	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);
+	set_capacity(gd,
+		     (dev->vi->size *
+		      dev->vi->usable_leb_size) >> 9);
+	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;
+
+	/* Stolen 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;
+	}
+
+	add_disk(dev->gd);
+
+	dev_info(disk_to_dev(dev->gd),
+		 "created from ubi%d:%d(%s)\n", dev->ubi_num, dev->vol_id,
+		 dev->vi->name);
+
+	kfree(dev->vi);
+	dev->vi = NULL;
+	ubi_close_volume(dev->desc);
+	dev->desc = NULL;
+	mutex_unlock(&dev->vol_lock);
+
+	mutex_unlock(&devlist_lock);
+
+	return 0;
+
+out_thread:
+	blk_cleanup_queue(dev->rq);
+out_queue:
+	put_disk(dev->gd);
+out_disk:
+	kfree(dev->vi);
+	dev->vi = NULL;
+out_info:
+	ubi_close_volume(dev->desc);
+	dev->desc = NULL;
+out_vol:
+	mutex_unlock(&dev->vol_lock);
+out_devlist:
+	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;
+	}
+
+	if (dev->desc) {
+		mutex_unlock(&devlist_lock);
+		return -EBUSY;
+	}
+
+	del_gendisk(dev->gd);
+	blk_cleanup_queue(dev->rq);
+	kthread_stop(dev->req_task);
+	put_disk(dev->gd);
+
+	kfree(dev->vi);
+
+	list_del(&dev->list);
+	kfree(dev);
+
+	mutex_unlock(&devlist_lock);
+	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;
+
+	/* 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);
+	set_capacity(dev->gd,
+		     (vi->size * vi->usable_leb_size) >> 9);
+	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;
+}
+
+#ifdef CONFIG_COMPAT
+static long ubiblk_ctrl_compat_ioctl(struct file *file, unsigned int cmd,
+				     unsigned long arg)
+{
+	unsigned long translated_arg = (unsigned long)compat_ptr(arg);
+
+	return ubiblk_ctrl_ioctl(file, cmd, translated_arg);
+}
+#endif
+
+/* ubiblk control device (receives ioctls) */
+static const struct file_operations ubiblk_ctrl_ops = {
+	.owner = THIS_MODULE,
+	.unlocked_ioctl = ubiblk_ctrl_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl = ubiblk_ctrl_compat_ioctl,
+#endif
+	.llseek = no_llseek,
+};
+static struct miscdevice ctrl_dev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "ubiblk_ctrl",
+	.fops = &ubiblk_ctrl_ops,
+};
+
+/**
+ * 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;
+
+	mutex_lock(&devlist_lock);
+
+	ret = misc_register(&ctrl_dev);
+	if (ret) {
+		pr_err("can't register control device\n");
+		goto out_unreg_blk;
+	}
+
+	ret = ubi_register_volume_notifier(&ubiblk_notifier, 1);
+	if (ret < 0)
+		goto out_unreg_ctrl;
+
+	mutex_unlock(&devlist_lock);
+	pr_info("major device number is %d\n", ubiblk_major);
+
+	return ret;
+
+out_unreg_ctrl:
+	misc_deregister(&ctrl_dev);
+out_unreg_blk:
+	unregister_blkdev(ubiblk_major, "ubiblk");
+
+	mutex_unlock(&devlist_lock);
+	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 list_head *list_ptr, *next;
+	struct ubiblk_dev *dev;
+
+	ubi_unregister_volume_notifier(&ubiblk_notifier);
+	misc_deregister(&ctrl_dev);
+
+	list_for_each_safe(list_ptr, next, &ubiblk_devs) {
+		dev = list_entry(list_ptr, struct ubiblk_dev, list);
+
+		/* TODO: it shouldn't happen, right ? */
+		if (dev->desc)
+			ubi_close_volume(dev->desc);
+
+		del_gendisk(dev->gd);
+		blk_cleanup_queue(dev->rq);
+		kthread_stop(dev->req_task);
+		put_disk(dev->gd);
+
+		kfree(dev->vi);
+		list_del(&dev->list); /* really needed ? */
+		kfree(dev);
+	}
+
+	unregister_blkdev(ubiblk_major, "ubiblk");
+	pr_info("end of life\n");
+}
+
+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..61df415
--- /dev/null
+++ b/include/mtd/ubiblk-user.h
@@ -0,0 +1,47 @@
+/*
+ * 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
+ */
+struct ubiblk_ctrl_req {
+	__s32 ubi_num;
+	__s32 vol_id;
+} __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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