Re: [libvirt] [PATCH v1] qemu-migration: Disallow migration of read only disk
On 08/10/2016 09:16 AM, Koniszewski, Pawel wrote:
> -----Original Message-----
> From: libvir-list-bounces(a)redhat.com [mailto:libvir-list-
> bounces(a)redhat.com] On Behalf Of Corey S. McQuay
> Sent: Friday, August 5, 2016 8:34 PM
> To: jjherne(a)linux.vnet.ibm.com; libvir-list(a)redhat.com
> Cc: Corey S. McQuay <csmcquay(a)linux.vnet.ibm.com>
> Subject: [libvirt] [PATCH v1] qemu-migration: Disallow migration of read only
> disk
>
> From: "Corey S. McQuay" <csmcquay(a)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.