[RFC] ubiblk: read-only block layer on top of UBI

[david.wagner at free-electrons.com]

From: David Wagner <david.wagner at free-electrons.com>

It creates one device for each UBI volume and dynamically add/remove one when a
UBI volume is created or deleted : it registers to UBI notifications.  The
devices are names "ubiblkX_Y" where X is the UBI device number and Y is the
volume ID.

I'm submitting it for review, comments (on the concept as well as on the
implementation) and advice.  It is my first kernel module - a lot of code was
taken from mtd_blkdevs and some from gluebi.

It is only known to work well with SquashFS.  Tests reported that with other
filesystems (ext2/3 and vfat), some bytes in some files (I couldn't find any
pattern), when read through ubiblk, don't match the original content (the
content of a file becomes random on several "lines" and goes back to normal).
The reason for that is still unknown.

Some other known issues are listed in the commit message.

 drivers/mtd/ubi/Kconfig  |    9 +
 drivers/mtd/ubi/Makefile |    1 +
 drivers/mtd/ubi/ubiblk.c |  462 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 472 insertions(+), 0 deletions(-)
 create mode 100644 drivers/mtd/ubi/ubiblk.c

--
David Wagner, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com