[Qemu-devel] QCOW image corruption under QEMU 0.9.0

[J M Cerqueira Esteves <jmce@artenumerica.com>]

Greetings

I got some error messages shortly after booting a Debian guest under
QEMU 0.9.0.  I did not annotate those, but they made me believe there
could be disk access problems, and if fact something weird happened to
one of the disk images (this was using two images, for hda and hdb):

After shutting down the guest, I inspected its image files with
qemu-info, which reported for hda

image: nisaba.hda.qcow
file format: raw
virtual size: 4.3G (4596273152 bytes)
disk size: 4.3G

but hda was supposed to have a virtual size of approximately 20 GB,
QCOW2 format and a saved snapshot...

The hdb image still seems OK:

image: nisaba.hdb.qcow
file format: qcow2
virtual size: 2.0G (2147483648 bytes)
disk size: 216M
cluster_size: 4096
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         20070217                66M 2007-02-17 05:58:40   46:06:17.193

I'll keep a copy of the damaged image in case someone competent on qemu
and qcow wishes to inspect it, but in case this may be suggestive:
I noticed that the only non-zero bytes until byte 12288 (where a first
'more random' sequence starts) are:
  byte 4102: 0x20
       4110: 0x30
       4118: 0x40
       ... and so on, until
       4206: 0xf0
       4221-4222: 0x0110
       4229-4230: 0x0120
       4237-4238: 0x0130
       4245-4246: 0x0140
       4252-4254: 0xd547b0
       4260-4262: 0xd547c0
        ...
       8180-8182: 0xd56660
       8188-8190: 0xd56670
       11776-11791: 0x6c6f3d 6c6f0a 6574 68303d 6574 68300a

Unvortunately I don't have an older copy of the hda image
with which to compare this broken one.  In any case
I have been running, in the same host, several 32-bit guests with Debian
and one with Windows XP, almost without any problems, first under QEMU
0.8.2 and since February 11 under QEMU 0.9.0 (with some images then
migrated from QCOW to QCOW2).

Details on the configuration:

Host: AMD Athlon 64 3500+ (HP dx5150 MT)
      with Ubuntu 6.06 LTS, kernel 2.6.15-28-amd64-k8.
VDE: 'backported' (just rebuilding the package)
     from Debian testing's vde 1.5.11-1.
QEMU: 0.9.0, configured with --cc=gcc-3.4 --enable-alsa
kqemu: 1.3.0pre11

Guest: Debian Etch (32-bit), with kernel 2.6.18-k7 (if I remember
       correctly);
       / was on hda, the failed image file;
       /tmp and swap on hdb, the surviving image.

QEMU was invoked with
vdeq qemu-system-x86_64 \
        -kernel-kqemu \
        -pidfile nisaba.pid \
        -m 192 \
        -std-vga \
        -net nic,vlan=0,model=rtl8139,macaddr=4A:4D:23:00:00:01 \
        -net vde,vlan=0,sock=/var/run/vde/tap-vde-1.ctl \
        -hda nisaba.hda.qcow -hdb nisaba.hdb.qcow

Best regards
                                  J Esteves