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

[Eric Blake <eblake@redhat.com>]

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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).

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


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