Re: [Qemu-devel] [PATCH] block/raw-posix: use seek_hole ahead of fiemap

[Kevin Wolf <kwolf@redhat.com>]

Am 25.09.2014 um 08:21 hat Markus Armbruster geschrieben:
> Please copy Kevin & Stefan for block patches.  Doing that for you.  I
> also copy Max, who left his fingerprints on commit 4f11aa8.
> 
> Tony Breeds <tony@bakeyournoodle.com> writes:
> 
> > The command
> >   qemu-img convert -O raw inputimage.qcow2 outputimage.raw
> >
> > intermittently creates corrupted output images, when the input image is not yet fully synchronized to disk.  This patch preferese the use of seek_hole checks to determine if the sector is present in the disk image.

Does this fix the problem or does it just make it less likely that it
becomes apparent?

If there is a data corruptor, we need to fix it, not just ensure that
only the less common environments are affected.

> > While we're there modify try_fiemap() to set FIEMAP_FLAG_SYNC.

That looks like a logically separate change, so it should probably be
a separate patch.

Is this fix for the corruptor? The commit message doesn't make it
clear. If so and fiemap is safe now, why would we still prefer
seek_hole?

> > Reported-By: Michael Steffens <michael_steffens@posteo.de>
> > CC: Pádraig Brady <pbrady@redhat.com>
> > Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>

Kevin