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

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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>
This commit is contained in:
Ezequiel Garcia
2014-02-25 13:25:22 -03:00
committed by Artem Bityutskiy
parent 5547fec74a
commit 9d54c8a33e
7 changed files with 718 additions and 0 deletions
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11
include/uapi/mtd/ubi-user.h
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@@ -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