Re: [PATCH 05/25] vfs: avoid problematic remapping requests into partial EOF block

Dave Chinner
2018-10-12T00:16:16Z

On Wed, Oct 10, 2018 at 09:12:54PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
>
> A deduplication data corruption is exposed by fstests generic/505 on
> XFS. It is caused by extending the block match range to include the
> partial EOF block, but then allowing unknown data beyond EOF to be
> considered a "match" to data in the destination file because the
> comparison is only made to the end of the source file. This corrupts the
> destination file when the source extent is shared with it.
>
> The VFS remapping prep functions only support whole block dedupe, but
> we still need to appear to support whole file dedupe correctly. Hence
> if the dedupe request includes the last block of the souce file, don't
> include it in the actual dedupe operation. If the rest of the range
> dedupes successfully, then reject the entire request. A subsequent
> patch will enable us to shorten dedupe requests correctly.

Ok, so this patch rejects whole file dedupe requests, and then a
later patch adds support back in for it?

Doesn't that leave a bisect landmine behind? Why separate the
functionality like this?

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com