Re: Qemu-KVM Livate Migration 0.12.2 -> 0.12.3/4 broken?

[Juan Quintela <quintela@redhat.com>]

Avi Kivity <avi@redhat.com> wrote:
> On 05/12/2010 02:11 AM, Juan Quintela wrote:
>> Peter Lieven<pl@dlh.net>  wrote:
>>    
>>> Hi Qemu/KVM Devel Team,
>>>
>>> Live Migration from a 0.12.2 qemu-kvm to a 0.12.3 (and 0.12.4)
>>> does not work: "load of migration failed"
>>>
>>> Is there any way to find out, why exactly it fails? I have
>>> a lot of VMs running on 0.12.2 and would like to migrate
>>> them to 0.12.4
>>>
>>> cmdline:
>>> -net tap,vlan=6,script=no,downscript=no,ifname=tap7 -net
>>> nic,vlan=6,model=e1000,macaddr=52:54:00:fe:00:88   -net
>>> tap,vlan=651,script=no,downscript=no,ifname=tap8 -net
>>> nic,vlan=651,model=e1000,macaddr=52:54:00:ff:00:69   -drive
>>> file=/dev/mapper/iqn.2001-05.com.equallogic:0-8a0906-b6eca7604-6280020bc4b4bde8-quagga,if=ide,boot=on,cache=none,aio=native
>>> -m 256 -monitor tcp:0:4090,server,nowait -vnc :90 -name 'Quagga' -boot
>>> order=dc,menu=on  -k de  -incoming tcp:172.21.59.132:5090 -pidfile
>>> /var/run/qemu/vm-148.pid  -rtc base=utc,clock=vm  -usb -usbdevice
>>> tablet  -no-kvm-irqchip  -vga cirrus
>>>
>>> Any hints would be appreciated!
>>>      
>> Can you try reverting this patch?
>>
>> commit 3fa017e24b0a0f0e68619a689b9b02fe486dae9e
>> Author: Marcelo Tosatti<mtosatti@redhat.com>
>> Date:   Thu Feb 11 18:19:44 2010 -0200
>>
>>      ide save/restore pio/atapi cmd transfer fields and io buffer
>>
>> and told me if it works?
>>
>>    
>
> Any idea why it fails?  And how to fix it?

Lack of "proper" subsections.  IDE is something like:

const VMStateDescription vmstate_ide_drive = {
    .version_id = 4,
....
}

static const VMStateDescription vmstate_bmdma = {
    .name = "ide bmdma",
    .version_id = 4,
...
}

const VMStateDescription vmstate_ide_pci = {
    .name = "ide",
    .version_id = 4,
....
        VMSTATE_STRUCT_ARRAY(bmdma, PCIIDEState, 2, 0,
                     vmstate_bmdma, BMDMAState),
        VMSTATE_IDE_DRIVES(bus[0].ifs, PCIIDEState),
        VMSTATE_IDE_DRIVES(bus[1].ifs, PCIIDEState),
....
}


Notice that everything is at version 4.  It used to be everything at
version 3.  Now the problem is that when migrating from v3 -> v4.  We
put in one place v3, But we only have a version number at the toplevel,
rest of "subsections" don't sent a version number.  There is no way to
fix it in the general case.  We can hack something around for ide, but
that will just be a hack, or we can backport marcelo change and port it
as a proper subsection (that is my plan).  I expect to have time at the
end of next time to work on this.

So, to make the story short: I know what is happening, and I know how to
fix it, just that fix is not trivial.  I just need time.

Later, Juan.