[BUG] 2.6.8-rc3 jffs2 unable to read filesystems

[Russell King]

The following two messages sum up the problem:

JFFS2 compression type 0x5a06 not avaiable.
Error: jffs2_decompress returned -5

It appears that a jffs2 change committed on July 15th has caused recent
2.6.8-rc kernels to be incompatible with jffs2 filesystems modified by
previous kernel versions.

The "new format" jffs2 filesystem uses both "compr" and "usercompr"
of the jffs2_raw_inode structure, whereas previous implementations
left "usercompr" uninitialised and thus contains random data.

This can be seen by tracing through the code from jffs2_alloc_raw_inode()
and noticing that previous implementations do not initialise this field -
AFAICS kmem_cache_alloc() does not guarantee that memory returned by
this function will be initialised.

Therefore, recent 2.6.8-rc kernels must _NOT_ use this field if they
wish to remain compatible with existing jffs2 filesystems.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core