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

[Anthony Liguori <aliguori@us.ibm.com>]

On 03/09/2012 12:45 PM, Eric Blake wrote:
> On 03/09/2012 11:31 AM, Anthony Liguori wrote:
>> On 03/09/2012 12:20 PM, Jan Kiszka wrote:
>>> On 2012-03-09 19:13, Luiz Capitulino wrote:
>>>> The Monitor object is passed back and forth within the migration/savevm
>>>> code so that it can print errors and progress to the user.
>>>>
>>>> However, that approach assumes a HMP monitor, being completely invalid
>>>> in QMP.
>>>>
>>>> This commit drops almost every single usage of the Monitor object, all
>>>> monitor_printf() calls have been converted into DPRINTF() ones.
>>>
>>> I guess for most printfs, this is OK. But do you provide an alternative
>>> for the block migration progress output? I did not find anything on
>>> first glance. That is not a debugging feature.
>>
>> The block migration progress stuff is horribly broken and I regret ever
>> merging it.  Are you actively relying on this?
>>
>> Does block migration even work?
>>
>> 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?

> but it is
> untested; if, as you say, it is horribly broken, then libvirt needs to
> pass on the error message back to the user that it is broken.  But we
> regularly get people complaining that they don't have shared storage set
> up, and they are looking for a magic bullet that will do block migration
> alongside the domain migration; perhaps libvirt can still provide that
> with block mirroring or other (working) solutions from the same API it
> gives to the user if you end up pulling it out of the migrate QMP
> command.

Well block mirroring is hopefully around the corner.

Regards,

Anthony Liguori

> At the end of the day, it's your call whether to pull it out,
> and libvirt will adapt, but it would be nice to know what kosher working
> alternative(s) to use instead.
>