FW: Xen 3.3.0 - QEMU COW disk image with sparse backing file - VM fails to start

["Martin Tröster" <TroyMcClure@web.de>]

Hi, 

I posted my problem to start QCOW based disk images on Xen 3.3 below at xen-users already, but as I did not get any responses yet, I directly contacted K. Wolf (as a frequent contributor in the QEMU Xen code). He suggested to post my problem here at xen-devel. Please see the quoted mail below for a detailled description on how my problem occurs. Furthermore, Kevin pointed me to this patch on Xen-changelog, which probably introduced the problem I am seeing:
http://lists.xensource.com/archives/html/xen-changelog/2008-10/msg00132.html

WIth help of this information, I probably might have a try to undo the changes in a private Xen build, but this does not sound like a good long-term option, especially for somebody not too deep into Xen/Qemu development...

Therefore, let me kindly ask why it is considered to "handle QCOW backing files correctly" now? The patch, in my eyes, allows to use a raw file as backing file, but breaks the use of a QCOW file (sparse file, in my setup) as a backing file. In my setup, this breaks the use of all current QCOW-files I am running when migrating from Xen-3.2 to Xen-3.3.

Although I cannot easily provide a fix by myself, I'd really like to have an approach both allowing to use QCOW- _and_ raw images as backing builds. Any help here is appreciated.

Thanks!

Cheers,
Martin

> -----Ursprüngliche Nachricht-----
> Von: "Martin Tröster" <TroyMcClure@web.de>
> Gesendet: 20.01.09 16:22:12
> An: xen-users@lists.xensource.com
> Betreff: Xen 3.3.0 - QEMU COW disk image with sparse backing file - VM fails to start

> 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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