Re: [Qemu-devel] [BUG] qemu-1.1.2 [FIXED-BY] qcow2: Fix avail_sectors in cluster allocation code

[Philipp Hahn]

Hello Kevin, 

Am Mittwoch 12 Dezember 2012 14:41:49 schrieb Kevin Wolf:
> As you can see in the commit message of that patch I was convinced that
> no bug did exist in practice and this was only dangerous with respect to
> future changes. Therefore my first question is if you're using an
> unmodified upstream qemu or if some backported patches are applied to
> it? If it's indeed unmodified, we should probably review the code once
> again to understand why it makes a difference.

This were all unmodified versions directly from git between "qemu-kvm-1.1.0" 
and "qemu-kvm-1.2.0"

"git checkout b7ab0fea37c15ca9e249c42c46f5c48fd1a0943c" works,
"git checkout b7ab0fea37c15ca9e249c42c46f5c48fd1a0943c~1" is broken.
"git checkout qemu-kvm-1.1.2"  is broken,
"git checkout qemu-kvm-1.1.2 ; git cherry-pick 
b7ab0fea37c15ca9e249c42c46f5c48fd1a0943c"  works

> In any case, this is the cluster allocation code. It's probably not
> related to rereading things from disk, but rather to the writeout of the
> page cache.

Yes, the problem is probably write related. But as the write "doens't explode 
with some spectacular error", I only notice the error on the following read 
by comparing md5 sums.
I just re-checked it: After a reboot the md5sums are still invalid, so I guess 
the data is corrupted on writeout.

Sincerely
Philipp
-- 
Philipp Hahn           Open Source Software Engineer      address@hidden
Univention GmbH        be open.                       fon: +49 421 22 232- 0
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