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[Qemu-devel] [BUG] Qcow2 corruption on snapshot revert
From: |
Philipp Hahn |
Subject: |
[Qemu-devel] [BUG] Qcow2 corruption on snapshot revert |
Date: |
Thu, 4 Aug 2011 16:20:08 +0200 |
User-agent: |
KMail/1.9.10 (enterprise35 20100903.1171286) |
Hello,
it seems like I have discovered a bug in qemu-0.14.1 which corrupts Qcow2
image files when using internal snapshots.
I tied this both on an amd64 host running our Debian bases UCS distribution
(using pure qemu-kvm_0.14 and pure qemu-kvm_0.14.1) and also on a pure Debian
i386 sid installation (patched qemu-kvm_0.14.1).
I can reproducte this every time doing the following steps:
0. Create and install VM
1. Shut down VM
2. Create offline snapshot using "qemu-img snapshot -c Off image.qcow2"
3. Start VM
4. Create online snapshot using "savevm On"
5. Shut down VM
6. Revert to snapshot using "qemu-img snapshot -a Off image.qcow2"
Repeat step 6 three or more times and the Image is destroyed.
My guess is that this is a but in qemu-img, which is related to having an
online snapshot (VM running) while reverting to an offline snapshot (VM
stopped), because I wasn't able to reproduce this using only offline
snapshots or only online snapshots.
I have attached a shell script to reproduce this bug on all my runs.
* It both happens with kvm-0.14.1 and also with qemu-0.14.1.
* The cache stragtegy "writethrough" vs. "writeback" is irrelevant.
The script needs an image nameded "pmh_squeeze-0.qcow.bak2" of an VM where you
can login via serial console using "root" for login and "univention" for
password. You can use other images as well, as long as you modify the block
device from within the VM. You get get it from
<http://download.univention.de/download/temp/qemu-0.14-qcow2/>
There you will also find the beginning of a small Python program
called "qcow2.py" which can be used to dump the structure of an qcow2 file in
some more human readable format with some consistency checking.
Related links:
<http://git.kernel.org/?p=virt/kvm/qemu-kvm.git;a=commit;h=e11480db7ff15a9e878f6b3cc1199b439bf7c825>
<http://git.kernel.org/?p=virt/kvm/qemu-kvm.git;a=commit;h=f0aa7a8b2d518c54430e4382309281b93e51981a>
<http://lists.gnu.org/archive/html/qemu-devel/2011-04/msg01376.html>
<https://forge.univention.org/bugzilla/show_bug.cgi?id=22221>
Any help is appreciated.
Sincerely
Philipp Hahn
--
Philipp Hahn Open Source Software Engineer address@hidden
Univention GmbH Linux for Your Business fon: +49 421 22 232- 0
Mary-Somerville-Str.1 D-28359 Bremen fax: +49 421 22 232-99
http://www.univention.de/
22221_qemu_qcow2_bug.test
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- [Qemu-devel] [BUG] Qcow2 corruption on snapshot revert,
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