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

[Koniszewski, Pawel]

Oh, sorry, had this on my todo list and somehow missed it.

This looks ok, in my case read-only device is not part of migrate-disks parameter, so everything should be all right.

Thanks for testing it!

Kind Regards,
Pawel Koniszewski

> -----Original Message-----
> From: Jason J. Herne [mailto:jjherne at linux.vnet.ibm.com]
> Sent: Thursday, August 25, 2016 3:22 PM
> To: Corey S McQuay <csmcquay at linux.vnet.ibm.com>; Koniszewski, Pawel
> <pawel.koniszewski at intel.com>; libvir-list at redhat.com
> Subject: Re: [libvirt] [PATCH v1] qemu-migration: Disallow migration of read
> only disk
> 
> 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:
> https://www.redhat.com/archives/libvir-list/2016-August/msg00378.html
> 
> --
> -- Jason J. Herne (jjherne at linux.vnet.ibm.com)