Re: [Qemu-devel] [PATCH] Revert block-qcow2.c to kvm-72 version due to corruption reports

[Jamie Lokier <jamie@shareable.org>]

Anthony Liguori wrote:
> Well such a large reversion is a bad idea.  Can you git bisect to the 
> actual changeset that introduced the bug you see?

Have done, did you read the other thread?

Message-ID: <20090211114126.GC31997@shareable.org>
Subject: Re: qcow2 corruption observed, fixed by reverting old change

Jamie Lokier wrote:
> Kevin Wolf wrote:
> > Jamie Lokier schrieb:
> > > Although there are many ways to make Windows blue screen in KVM, in
> > > this case I've narrowed it down to the difference in
> > > qemu/block-qcow2.c between kvm-72 and kvm-73 (not -83).
> >
> > This must be one of SVN revisions 5003 to 5008 in upstream qemu. Can you
> > narrow it down to one of these? I certainly don't feel like reviewing
> > all of them once again.
> 
> It's QEMU SVN delta 5005-5006, copied below.

I don't have time to disentangle the different optimisations done to
qcow2 around that changeset, nor fix the changeset itself, but I can
test proposed patches on my guest VM image, which I've copied aside
because it's consistent about failing or not.

If nobody else has time either, then I think an imminent new QEMU
release, which may get rolled into distros and so on, is better off
with the the changes reverted than corrupting guest images.

I'm not proposing throwing away all the good work done on qcow2, only
that fixing observed corruption is important especially for a major
release, and reverting later changes can be temporary until the bug is
found and fixed.

-- Jamie