UBI: R/O block driver on top of UBI volumes

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

Artem: amend commentaries and massage the patch a little bit.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

6 files changed, 707 insertions, 0 deletions

diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index 36663af56d89..783fb186d876 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 b46b0c978581..4e3c3d70d8c3 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 000000000000..cea7d1cf9d04
--- /dev/null
+++ b/drivers/mtd/ubi/block.c
@@ -0,0 +1,646 @@
+/*
+ * 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, 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 += 1;
+                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 access anyway.
+         */
+        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_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 57deae961429..6e30a3c280d0 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 8ca49f2043e4..39d377489c29 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 8ea6297a208f..e76ff98440a4 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