[RFC PATCH v2 0/4] mtd: ubi: Enable accessing RO filesystems in UBI vols

[Sam Edwards <cfsworks@gmail.com>]

Hi list,

This is the second version of my RFC patchset to treat static UBI volumes as DM
block devices, allowing users to access read-only filesystems (SquashFS, EROFS)
contained within such volumes.

This is a rebased and updated version, as requested by Heiko.

Previously, we have agreed on a syntax, which my downstream is now starting to
use:
=> ls ubi 0:rootfs /boot
=> ls ubi 0:2 /boot

This is still not yet ready for mainline inclusion, because the actual UBI DM
access is happening in disk/part.c, which is not "clean" with the way the
DM/legacy switching is currently plumbed. I'm still looking for guidance on how
to name/implement block functions for looking up a *subvolume* block device by
type+parentidx+{name,ID}.

Changes v1->v2:
- Rebased onto next post-2023.10's release.
- Fix NULL dereference caused by passing NULL to `blk_create_device`
- Parse UBI index/volume numbers with `dectoul` instead of `hextoul`, to match
  Linux's behavior of treating these numbers as decimal.
- Do not treat a valid decimal number as a volume name, even if the volume ID
  doesn't exist, to match Linux's behavior of always treating decimal numbers
  as volume IDs.

Cheers,
Sam

Sam Edwards (4):
  mtd: ubi: register UBI attachments as DM devices
  mtd: ubi: bind block device driver for static volumes
  disk: part: fall-through if "ubi" requested but ubifs not mounted
  HACK: enable access to `ubi 0:volname` block devices

 cmd/ubi.c                    |  11 +++
 disk/part.c                  |  69 +++++++++++--
 drivers/mtd/ubi/Makefile     |   1 +
 drivers/mtd/ubi/ubi-uclass.c | 185 +++++++++++++++++++++++++++++++++++
 include/dm/uclass-id.h       |   1 +
 include/ubi_uboot.h          |   5 +
 6 files changed, 264 insertions(+), 8 deletions(-)
 create mode 100644 drivers/mtd/ubi/ubi-uclass.c

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2.41.0