Re: [Qemu-devel] [PATCH 1/5] monitor: screen_dump async

[Luiz Capitulino <lcapitulino@redhat.com>]

On Mon, 24 Oct 2011 17:13:14 +0200
Gerd Hoffmann <kraxel@redhat.com> wrote:

> On 10/24/11 14:02, Alon Levy wrote:
> > Make screen_dump monitor command an async command to allow next for qxl
> > to implement it as a initiating call to red_worker and completion on
> > callback, to fix a deadlock when issueing a screendump command via
> > libvirt while connected with a libvirt controlled spice-gtk client.
> 
> Approach looks reasonable to me.  Patch breaks the build though, you've
> missed a bunch of screen_dump functions in non-x86 targets.

There are two problems actually.

The first one is that changing an existing command from synchronous
to asynchronous is an incompatible change because asynchronous commands
semantics is different. For an example of possible problems please
check: https://bugzilla.redhat.com/show_bug.cgi?id=623903.

The second problem is that the existing asynchronous interface in the
monitor is incomplete and has never been used for real. Our plan is to
use QAPI's async support, but that has not landed in master yet and iirc
there wasn't consensus about it. I also think it's a bit late for its
inclusion in 1.0 (and certainly not a candidate for stable).

If all you need here is to delay sending the response, then maybe the
current interface could work (although I honestly don't trust it and
regret not having dropped it). Otherwise our only choice would be to
work on getting the QAPI async support merged.