[Xen-users] Xen 3.3.0 - QEMU COW disk image with sparse backing file - VM fails to start

[Martin Tröster <TroyMcClure@xxxxxx>]

Hi,

I upgraded my Xen 3.2-based test system to Xen 3.3. With this installation, I 
am no longer able to start images with COW disk images based on qcow sparse 
files. Starting the DomU via xm create gives success status (with "Startig 
Domain test" message printed to console), but xm list directly afterwards shows 
no entry for the VM.

The image structure is:
Base File A.img (sparse QCOW2 file)
COW File B.img (QCOW2 file with A.img as backing file) used as disk in Xen 
config file (see VM config file below)

I am running a CentOS 5.2 server with the pre-build packages at 
http://www.gitco.de/repro and can repro this behaviour on both 3.3.0 and 
3.3.1RC1_pre (no 3.3.1 final version available, no time yet to do a build on my 
own).

In detail, I see the following behaviour:
-> RAW image with disk using file:/ - works
-> QCOW sparse image using tap:qcow - works
-> QCOW image based on RAW image using tap:qcow - works
-> QCOW image based on QCOW sparse image using tap:qcow - fails.

Logs of failing case:
=============================
/var/log/xen/xend.log shows that the domain immediately terminates, but no 
ERROR indication:
[2009-01-20 09:13:55 20596] DEBUG (XendDomainInfo:1443) 
XendDomainInfo.handleShutdownWatch
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices vif.
[2009-01-20 09:13:55 20596] DEBUG (DevController:160) Waiting for 0.
[2009-01-20 09:13:55 20596] DEBUG (DevController:645) hotplugStatusCallback 
/local/domain/0/backend/vif/8/0/hotplug-status.
[2009-01-20 09:13:55 20596] DEBUG (DevController:645) hotplugStatusCallback 
/local/domain/0/backend/vif/8/0/hotplug-status.
[2009-01-20 09:13:55 20596] DEBUG (DevController:659) hotplugStatusCallback 1.
[2009-01-20 09:13:55 20596] DEBUG (DevController:160) Waiting for 1.
[2009-01-20 09:13:55 20596] DEBUG (DevController:645) hotplugStatusCallback 
/local/domain/0/backend/vif/8/1/hotplug-status.
[2009-01-20 09:13:55 20596] DEBUG (DevController:659) hotplugStatusCallback 1.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices vscsi.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices vbd.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices irq.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices vkbd.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices vfb.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices 
console.
[2009-01-20 09:13:55 20596] DEBUG (DevController:160) Waiting for 0.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices pci.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices 
ioports.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices tap.
[2009-01-20 09:13:55 20596] DEBUG (DevController:160) Waiting for 51712.
[2009-01-20 09:13:55 20596] DEBUG (DevController:645) hotplugStatusCallback 
/local/domain/0/backend/tap/8/51712/hotplug-status.
[2009-01-20 09:13:55 20596] DEBUG (DevController:659) hotplugStatusCallback 1.
[2009-01-20 09:13:55 20596] DEBUG (DevController:155) Waiting for devices vtpm.
[2009-01-20 09:13:55 20596] INFO (XendDomain:1172) Domain test (8) unpaused.
[2009-01-20 09:13:57 20596] INFO (XendDomainInfo:1634) Domain has shutdown: 
name=test id=8 reason=poweroff.
[2009-01-20 09:13:57 20596] DEBUG (XendDomainInfo:2389) XendDomainInfo.destroy: 
domid=8
[2009-01-20 09:13:57 20596] DEBUG (XendDomainInfo:2406) 
XendDomainInfo.destroyDomain(8)
[2009-01-20 09:13:57 20596] DEBUG (XendDomainInfo:1939) Destroying device model
[2009-01-20 09:13:57 20596] DEBUG (XendDomainInfo:1946) Releasing devices
[2009-01-20 09:13:57 20596] WARNING (image:472) domain test: device model 
failure: no longer running; see /var/log/xen/qemu-dm-test.log 

/var/log/xen/qemu-dm-test.log shows nothing spectacular at all (at least for 
me):
domid: 8
qemu: the number of cpus is 1
config qemu network with xen bridge for  tap8.0 xenbr0
config qemu network with xen bridge for  tap8.1 eth0
Using xvda for guest's hda
Strip off blktap sub-type prefix to /path/to/test.img (drv 'qcow')
Watching /local/domain/0/device-model/8/logdirty/next-active
Watching /local/domain/0/device-model/8/command
qemu_map_cache_init nr_buckets = 10000 size 3145728
shared page at pfn 3fffe
buffered io page at pfn 3fffc
Time offset set 0
Register xen platform.
Done register platform.

/var/log/messages also shows nothing remarkable. Interesting entries never seen 
before are:
Jan 19 17:50:02 test kernel: tapdisk[21929] general protection rip:40b315 
rsp:42900108 error:0
but they occur all the time on Xen 3.3 and Xen 3.3.1 using qcow images (but 
seem to be recovered)

VM config file:
------------------------------------------------------------------------------------------
name = "test"
device_model = '/usr/lib64/xen/bin/qemu-dm'
builder = "hvm"
kernel =  "/usr/lib/xen/boot/hvmloader"

# hardware
memory = "1024"
disk =  [ 'tap:qcow:/path/to/B.img,ioemu:xvda,w' ]
vcpus=1

# network
vif = [ 
'type=ioemu,mac=02:00:00:00:00:01','type=ioemu,bridge=eth0,mac=02:00:00:00:01:98'
 ]
dhcp = "dhcp"

# visualization
sdl = 0
vnc = 1
vncviewer = 0
------------------------------------------------------------------------------------------

Any help is appreciated. Thanks!

Cheers,
Martin
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