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

-----Original Message----- From: Jason J. Herne [mailto:jjherne@linux.vnet.ibm.com] Sent: Thursday, August 25, 2016 3:22 PM To: Corey S McQuay <csmcquay(a)linux.vnet.ibm.com>; Koniszewski, Pawel <pawel.koniszewski(a)intel.com>; libvir-list(a)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(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&gt; >>>> Subject: [libvirt] [PATCH v1] qemu-migration: Disallow migration of >>>> read only disk >>>> >>>> From: "Corey S. McQuay" <csmcquay(a)linux.vnet.ibm.com&gt; >>>> >>>> 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(a)linux.vnet.ibm.com)