[libvirt] [PATCH v3 3/6] qemuMigrationDriveMirror: Listen to events

[Jiri Denemark]

On Fri, Feb 13, 2015 at 16:24:30 +0100, Michal Privoznik wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1179678
> 
> When migrating with storage, libvirt iterates over domain disks and
> instruct qemu to migrate the ones we are interested in (shared, RO and
> source-less disks are skipped). The disks are migrated in series. No
> new disk is transferred until the previous one hasn't been quiesced.
> This is checked on the qemu monitor via 'query-jobs' command. If the
> disk has been quiesced, it practically went from copying its content
> to mirroring state, where all disk writes are mirrored to the other
> side of migration too. Having said that, there's one inherent error in
> the design. The monitor command we use reports only active jobs. So if
> the job fails for whatever reason, we will not see it anymore in the
> command output. And this can happen fairly simply: just try to migrate
> a domain with storage. If the storage migration fails (e.g. due to
> ENOSPC on the destination) we resume the host on the destination and
> let it run on partly copied disk.
> 
> The proper fix is what even the comment in the code says: listen for
> qemu events instead of polling. If storage migration changes state an
> event is emitted and we can act accordingly: either consider disk
> copied and continue the process, or consider disk mangled and abort
> the migration.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  src/qemu/qemu_migration.c | 37 +++++++++++++++++--------------------
>  1 file changed, 17 insertions(+), 20 deletions(-)

ACK, please push patches 1..3 since I realized turning all this into a
condition is not going to be that easy...

Jirka