Re: [PATCH v2 27/28] ext4: xattr inode deduplication

[Darrick J. Wong]

On Fri, Jun 02, 2017 at 05:46:22AM -0700, Tahsin Erdogan wrote:
> > Hmm... normally we'd supply sbi->s_csum_seed as the second argument so
> > that the metadata checksum value also has the fs uuid stamped into it.
> 
> I have thought about using sbi->s_csum_seed and was a little hesitant
> because it involves adding more complexity to e2fsprogs to handle
> cases like changing uuid or turning off metadata_csum. After thinking
> more about this, I think it is doable.

e2fsprogs already has code to walk the fs to rewrite/remove checksums,
so it shouldn't be too much effort to tap into that to rewrite the
ea_info hash.

> > Even if you dismiss that, we usually follow the convention of
> > initializing the crc32c calculation with (~0U), not (0U), to strengthen
> > crc32c's ability to detect zeroes being injected at the start of the
> > stream.
> 
> Agreed, using ~0 is definitely better than 0.

--D