Re: [Qemu-devel] [PATCH 2/10] Allow the monitor to be suspended during non-blocking op

Chris Lalancette
2008-09-10T13:39:09Z

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Live migration happens in the background, but it is useful to make the monitor
>> command appear as if it's blocking. This allows a management tool to
>> immediately know when the live migration has completed without having to poll
>> the migration status.
>>
>> This patch allows the monitor to be suspended from a monitor callback which
>> will prevent new monitor commands from being executed.
>>
>>
>
> This means that migration is no longer transparent. While migration is
> going on, you can't change the cdrom media, look at cpu registers, or do
> anything that requires the monitor.
>
> This both reduces the functionality and complicates management
> applications. IMO migration should have asynchronous notification (and
> no, I don't think multiple monitors is the correct solution).
>

Despite Avi's objections, I'm OK with this, as long as the user of the monitor
has an option. That is, if the user can pass some switch to say "don't suspend
the monitor while I'm migrating", then that's fine. Actual people at the
console will pass that switch, and the management tools won't (or vice-versa; I
don't really care what the default is). This is really no different from the
situation we currently have in KVM, where you pass -d to do it in the
background, and pass no options to do it in the foreground.

(looking ahead into patch 10/10, it doesn't look like there is currently an
option, but we should add one).

Chris Lalancette