[libvirt] [PATCH v1] qemu-migration: Disallow migration of read only disk

Jason J. Herne jjherne at linux.vnet.ibm.com
Thu Aug 25 13:22:09 UTC 2016

On 08/17/2016 05:10 PM, Jason J. Herne wrote:
> On 08/11/2016 08:57 AM, Corey S McQuay wrote:
>> On 08/10/2016 09:16 AM, Koniszewski, Pawel wrote:
>>>> -----Original Message-----
>>>> From: libvir-list-bounces at redhat.com [mailto:libvir-list-
>>>> bounces at redhat.com] On Behalf Of Corey S. McQuay
>>>> Sent: Friday, August 5, 2016 8:34 PM
>>>> To: jjherne at linux.vnet.ibm.com; libvir-list at redhat.com
>>>> Cc: Corey S. McQuay <csmcquay at linux.vnet.ibm.com>
>>>> Subject: [libvirt] [PATCH v1] qemu-migration: Disallow migration of
>>>> read only
>>>> disk
>>>> From: "Corey S. McQuay" <csmcquay at linux.vnet.ibm.com>
>>>> Currently Libvirt allows attempts to migrate read only disks. Qemu
>>>> cannot
>>>> handle this as read only disks cannot be written to on the
>>>> destination system.
>>>> The end result is a cryptic error message and a failed migration.
>>>> This patch causes migration to fail earlier and provides a meaningful
>>>> error
>>>> message stating that migrating read only disks is not supported.
>>> What will happen if read-only disk is copied to destination prior to
>>> migration start? Currently such scenario works, will it still work
>>> with this code?
>> Based on our testing, pre-copying a read only disk image to the
>> destination system has no effect on the outcome of attempting to migrate
>> a non-shared read only disk. I'm not sure what scenario you are
>> referring to but here is what we tried:
>> Relevant guest xml:
>>      <disk type='file' device='cdrom'>
>>        <driver name='qemu' type='raw' cache='writethrough'/>
>>        <source file='/disk-images/guest.iso'/>
>>        <backingStore/>
>>        <target dev='sdz' bus='scsi'/>
>>        <readonly/>
>>        <alias name='scsi0-0-0-0'/>
>>        <address type='drive' controller='0' bus='0' target='0' unit='0'/>
>>      </disk>
>> The disk image exists at /disk-images/guest.iso on the source. Before
>> migration we copied the image to the same path on the destination
>> system. Then we attempted migration:
>>      virsh migrate --live --copy-storage-all --migrate-disks sdz
>> --verbose kvm1 qemu+ssh://dstHost/system tcp://dstHost
>> The error message we get is:
>> error: internal error: info migration reply was missing return status
>> Running journalctl shows additional information:
>> Aug 10 16:02:16 collin-kvm libvirtd[41616]: operation failed: migration
>> of disk sdz failed.
>> I'm pretty sure this patch does not stop the user from doing anything
>> that works today. But if your scenario is different from ours in some
>> way please let us know and we'll do some more testing.
> Pawel,
> Thanks for taking a look. Does Corey's reply address your concerns?

Polite ping for Pawel, and anyone else who wants to review. Thanks :)

Original patch here:

-- Jason J. Herne (jjherne at linux.vnet.ibm.com)

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