Re: [Qemu-devel] [RFC v4 9/9] qxl-render: call ppm_save on bh

[Gerd Hoffmann <kraxel@redhat.com>]

On 02/21/12 22:39, Alon Levy wrote:
> This changes the behavior of the monitor command. After the previous
> patch, there is no longer an option of deadlock with virt-manager, but
> ppm_save is called too early, before the update has completed. With this
> patch it is called at the correct moment, but that means there is a race
> between the monitor command completing and the screendump file being saved.
> 
> The only solution is to use an asynchronous monitor command. For a
> previous round of this see:
>  http://lists.gnu.org/archive/html/qemu-devel/2011-10/msg02810.html
> 
> Since that's contentious, I'm suggesting we do something that is almost
> correct and doesn't hang, instead of correct and hangs. The screendump
> user can inotify on the directory and the file if need be. For casual
> monitor usage there is no difference.

I still think we should defer that and figure how to fix that properly,
either using (internally) async monitor commands via qapi, or using an
event.

> +typedef struct QXLPPMSaveBHData {
> +    PCIQXLDevice *qxl;
> +    QXLCookie *cookie;
> +} QXLPPMSaveBHData;

Is there a need for a separate struct?  I think you can just stick the
filename into the QXLCookie struct, then write out screen shots in the
update area bottom half, no?

cheers,
  Gerd