Re: [Qemu-devel] qcow2 corruption observed, fixed by reverting old change

Kevin Wolf
2009-02-11T12:34:32Z

Jamie Lokier schrieb:
> 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've tested by applying the diffs up to QEMU SVN revs 5003 to 500,
> onto kvm-72, and 5005-5006 is the diff which triggers the failed guest
> boot, consistently.

That's exactly what I was afraid of... It's the most difficult patch of
the series. I'm adding Laurent to CC who wrote the patch series then,
but I can imagine he wants to do different things in his spare time.

Besides reviewing the code over and over again, I think the only real
chance is that you can get a non-productive copy of your image and add
some debug code so that we can see at least which code path is causing
problems.

> Aside from logic, the code mixes signed 32-bit with unsigned 64-bit
> with unclear naming which would make me nervous. My host is 64-bit,
> by the way.

I would suspect that simply having a 64 bit host isn't enough to trigger
the problem. These patches were in for half a year now without anyone
noticing such failure.

By the way and completely off-topic: Have you already tried to use the
VHD patches? I would really like to know if they fix your problems.

Kevin