linux/fs/romfs
Coly Li f598f82e20 romfs: use different way to generate fsid for BLOCK or MTD
Commit 8a59f5d252 ("fs/romfs: return f_fsid for statfs(2)") generates
a 64bit id from sb->s_bdev->bd_dev.  This is only correct when romfs is
defined with CONFIG_ROMFS_ON_BLOCK.  If romfs is only defined with
CONFIG_ROMFS_ON_MTD, sb->s_bdev is NULL, referencing sb->s_bdev->bd_dev
will triger an oops.

Richard Weinberger points out that when CONFIG_ROMFS_BACKED_BY_BOTH=y,
both CONFIG_ROMFS_ON_BLOCK and CONFIG_ROMFS_ON_MTD are defined.
Therefore when calling huge_encode_dev() to generate a 64bit id, I use
the follow order to choose parameter,

- CONFIG_ROMFS_ON_BLOCK defined
  use sb->s_bdev->bd_dev
- CONFIG_ROMFS_ON_BLOCK undefined and CONFIG_ROMFS_ON_MTD defined
  use sb->s_dev when,
- both CONFIG_ROMFS_ON_BLOCK and CONFIG_ROMFS_ON_MTD undefined
  leave id as 0

When CONFIG_ROMFS_ON_MTD is defined and sb->s_mtd is not NULL, sb->s_dev
is set to a device ID generated by MTD_BLOCK_MAJOR and mtd index,
otherwise sb->s_dev is 0.

This is a try-best effort to generate a uniq file system ID, if all the
above conditions are not meet, f_fsid of this romfs instance will be 0.
Generally only one romfs can be built on single MTD block device, this
method is enough to identify multiple romfs instances in a computer.

Link: http://lkml.kernel.org/r/1482928596-115155-1-git-send-email-colyli@suse.de
Signed-off-by: Coly Li <colyli@suse.de>
Reported-by: Nong Li <nongli1031@gmail.com>
Tested-by: Nong Li <nongli1031@gmail.com>
Cc: Richard Weinberger <richard.weinberger@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-01-24 16:26:14 -08:00
..
Kconfig NOMMU: Fix the RomFS Kconfig to ensure at least one backing store is selected 2009-03-24 09:02:39 +00:00
Makefile NOMMU: Make it possible for RomFS to use MTD devices directly 2009-03-24 09:01:32 +00:00
internal.h ROMFS: romfs_lookup() shouldn't be doing a partial name comparison 2009-04-24 13:28:31 -07:00
mmap-nommu.c make new_sync_{read,write}() static 2015-04-11 22:29:40 -04:00
storage.c romfs: switch to new MTD API 2012-03-27 00:19:30 +01:00
super.c romfs: use different way to generate fsid for BLOCK or MTD 2017-01-24 16:26:14 -08:00