QEmu 1.3+ cannot restore a 1.1- live snapshot made in qemu-kvm

[Francois Gouget]

I have upgraded to QEmu 1.3.90 (Debian 1.4.0~rc0+dfsg-1exp) but now when I try to restore a live snapshot made in QEmu 1.1.2 (Debian 1.1.2+dfsg-5) I get the following message:

virsh # snapshot-revert fgtbbuild wtb
error: operation failed: Error -22 while loading VM state

I have test VMs with live snapshots coreresponding to different testing configurations. So I typically revert the VMs in one of the live snapshots and run the tests. It would be pretty annoying to have to recreate all these live snapshots any time I upgrade QEmu.

ipxe-qemu 1.0.0+git-20120202.f6840ba-3
qemu 1.4.0~rc0+dfsg-1exp
qemu-keymaps 1.4.0~rc0+dfsg-1exp
qemu-kvm 1.4.0~rc0+dfsg-1exp
qemu-system 1.4.0~rc0+dfsg-1exp
qemu-system-arm 1.4.0~rc0+dfsg-1exp
qemu-system-common 1.4.0~rc0+dfsg-1exp
qemu-system-mips 1.4.0~rc0+dfsg-1exp
qemu-system-misc 1.4.0~rc0+dfsg-1exp
qemu-system-ppc 1.4.0~rc0+dfsg-1exp
qemu-system-sparc 1.4.0~rc0+dfsg-1exp
qemu-system-x86 1.4.0~rc0+dfsg-1exp
qemu-user 1.4.0~rc0+dfsg-1exp
qemu-utils 1.4.0~rc0+dfsg-1exp
libvirt-bin 1.0.2-1
libvirt-dev 1.0.2-1
libvirt-doc 1.0.2-1
libvirt-glib-1.0-0 0.1.2-1
libvirt0 1.0.2-1
libvirtodbc0 6.1.4+dfsg1-5

[Michael Tokarev (mjt+launchpad-tls)]

This sounds pretty much like a prob with video ram size. In 1.1.x, we had video ram of 8Mb, in 1.3 it is 16Mb... should this be a problem, to come from smaller to larger size?

Besides that, debian uses almost unmodified qemu, so the same prob should exist for upstream qemu too.

But at any rate, I never recommended any sort of cross-version migration as in practice, despite countless efforts spent to make it to work, it almost always does NOT work.

Thanks,

/mjt

[Michael Tokarev (mjt+launchpad-tls)]

And one more thing -- from what to what are you trying to migrate? I see you have qemu-kvm installed too, -- were you using it previously? Note that qemu-kvm 1.1 had the same video ram size = 16Mb as current qemu have. But my cross-version migration comment stays and in this case it becomes even stronger.

[Francois Gouget (fgouget)]

> And one more thing -- from what to what are you trying to migrate?

I believe kvm is being used in both cases, though the command is different with QEmu 1.3.90. I have redone tests where I kept libvirt set to 1.0.2 and only switched between QEmu 1.1.2 and 1.3.90 to minimize the changes. So here the only difference is 'apt-get install -t experimental qemu'.

Here is what 'ps aux' shows me:

libvirt 1.0.2-2 + QEmu 1.1.2

127 12841 92.7 4.6 1078272 189128 ? Sl 00:45 10:46 /usr/bin/kvm -name fgtbwinxp -S -M pc-1.1 -cpu Penryn,+pdcm,+xtpr,+tm2,+est,+smx,+vmx,+ds_cpl,+monitor,+dtes64,+pbe,+tm,+ht,+ss,+acpi,+ds,+vme -enable-kvm -m 768 -smp 2,sockets=2,cores=1,threads=1 -uuid e624f2c9-80fd-26c7-a38a-0f0e49b6b719 -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/fgtbwinxp.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=localtime -no-shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive file=/mnt/storage1/qemu/fgtbwinxp.img,if=none,id=drive-ide0-0-0,format=qcow2,cache=writeback -device ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 -drive if=none,id=drive-ide0-1-0,readonly=on,format=raw -device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -netdev tap,fd=23,id=hostnet0 -device rtl8139,netdev=hostnet0,id=net0,mac=52:54:00:c7:0e:97,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -device usb-tablet,id=input0 -vnc 127.0.0.1:0 -vga vmware -device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5 -loadvm wtb

With libvirt 1.0.2-2 + QEmu 1.3.90
127 18709 39.7 0.8 1075732 35304 ? Sl 01:39 0:05 qemu-system-x86_64 -machine accel=kvm:tcg -name fgtbwinxp -S -M pc-1.1 -cpu Penryn,+pdcm,+xtpr,+tm2,+est,+smx,+vmx,+ds_cpl,+monitor,+dtes64,+pbe,+tm,+ht,+ss,+acpi,+ds,+vme -m 768 -smp 2,sockets=2,cores=1,threads=1 -uuid e624f2c9-80fd-26c7-a38a-0f0e49b6b719 -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/fgtbwinxp.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=localtime -no-shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive file=/mnt/storage1/qemu/fgtbwinxp.img,if=none,id=drive-ide0-0-0,format=qcow2,cache=writeback -device ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 -drive if=none,id=drive-ide0-1-0,readonly=on,format=raw -device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -netdev tap,fd=23,id=hostnet0 -device rtl8139,netdev=hostnet0,id=net0,mac=52:54:00:c7:0e:97,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -device usb-tablet,id=input0 -vnc 127.0.0.1:0 -vga vmware -device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5 -loadvm wtb

There's a wrinkle I missed in my original report: the behavior is different depending on whether the VM is already running or not.

$ virsh --connect qemu:///system dest...

[Michael Tokarev (mjt+launchpad-tls)]

Ok, so this is migration from qemu-kvm 1.1 to qemu 1.3. This officially does not work because the two uses different memory layout.

There is a way to make this work from old qemu-kvm to new qemu, by patching new qemu, but this introduces incompatibilities in other areas.

Hopefully there will be no more "major" transitions like this in the future (I mean from qemu-kvm to qemu), so there's a chance that snapshots made with 1.3 and up will be forward-compatible.

While this bugreport is filed with debian versions in mind, we in debian especially did not apply any changes to upstream qemu in this area, -- as history shows, any attempt to "fix" this "downstream" only makes things worse.

[Thomas Huth (th-huth)]

I think we can close this ticket nowdays - as Michael mentioned in comment #4, migration between qemu-kvm and qemu was not supported, and the mentioned versions are pretty much outdated now anyway.