Re: [Qemu-devel] [RFC 5/7] qxl-render: call ppm_save on callback

[Alon Levy <alevy@redhat.com>]

On Mon, Feb 20, 2012 at 02:29:11PM -0700, Eric Blake wrote:
> On 02/20/2012 04:32 AM, Gerd Hoffmann wrote:
> > Hmm, that is pretty lame.  There are users like autotest which expect
> > the screen dump being there when the monitor command is finished, that
> > change will break them.
> 
> Libvirt is another such user.
> 
> > 
> > Unfortunaly there is no easy way out.  I think the options are:
> > 
> >  (1) Keep existing behavior.  That means the screenshot might show old
> >      screen content.  Not very nice too.  Would work sort-of ok for
> >      autotest though as autotest does screenshots every second and thus
> >      the screen content wouldn't be older than a second.
> > 
> >  (2) Async monitor command.  Keeps interface and works nicely.  A bunch
> >      of QAPI bits tickled into master meanwhile, so we could look at
> >      this again.  Luiz?  What is the status here?
> > 
> >  (3) Something like this patch + additionally introduce a
> >      "your-screenshot-is-finished-now" qmp event.  Will break existing
> >      users too.  But at least they can be adapted without requiring
> >      some external, nonportable service like inotify ...
> 
> Libvirt would want 3) - any command that becomes async also needs an
> event to tell us when the command is completed, so that libvirt can
> maintain the synchronous interface to the user (and/or expose a new flag
> to allow the user to also benefit from the asynchronous command).

If I do 2) then libvirt won't notice because the monitor command will
block as usual. Only change would be internal, qemu would continue
processing other fds in the interim.

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