Re: [Qemu-devel] [PATCH 3/4] Purge migration of (almost) everything to do with monitors

[Eric Blake <eblake@redhat.com>]

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On 03/09/2012 12:42 PM, Eric Blake wrote:
> On 03/09/2012 11:53 AM, Anthony Liguori wrote:
>>>>
>>>> Could we just remove block migration entirely...
>>>
>>> Libvirt has already exposed block migration to users,
>>
>> :-(
>>
>> Do you rely on the progress stats that are printed?
> 
> I've never personally used it (as I said earlier, the libvirt support
> for blk and inc doesn't get much testing), but I can state that if you do:
> 
> virsh migrate --copy-storage-all --copy-storage-inc --verbose ...
> 
> that virsh will cause libvirt to start up a detached migration, then
> repeatedly call the query-migrate monitor command to update an on-screen
> progress monitor to the user; this progress monitor tracks both ram and
> disk status to compute the percentage complete showed to the user, so at
> some level, libvirt really is trying to rely on accurate block migration
> progress numbers.

Just realized I wasn't very clear:

libvirt does _not_ play back qemu's status numbers, so much as computing
its _own_ progress monitor based on parsing the output of the repeated
query-migrate commands.  And since libvirt tends to favor QMP over HMP,
the only monitoring we need from QMP is what we query for; we don't need
HMP-style update messages.  Having HMP update a progress line each time
it rearms the one second timer while waiting for the migration to
complete is probably good enough for HMP, and libvirt won't care.

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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