Re: [Qemu-devel] [PATCH/RFC 0/7] Screendump to UNIX socket & in PNG format

[Luiz Capitulino]

On Wed, 14 Mar 2012 10:01:15 +0000
Stefan Hajnoczi <address@hidden> wrote:

> On Wed, Mar 14, 2012 at 9:51 AM, Gerd Hoffmann <address@hidden> wrote:
> >  Hi,
> >
> >> The most practical first step would be simply sending the ppm over a
> >> socket from ppm_save().  The 'screendump' command today already blocks
> >> so no new badness is being added.  There would be no threads or fancy
> >> image encoding.
> >
> > Adding scaling / compression support will add more overhead though, so
> > doing that without offloading screendump to a thread first is a bad idea
> > I think.  Or at least have some numbers to see how bad it actually is.
> 
> I agree, that's why I suggest sending the ppm over a socket.  It
> transports out the image data and QEMU itself doesn't do the
> encoding/scaling.

Just out of curiosity, are we planning to extend the current screendump
command or add a new one?

If we just extend the current command, then we'll have to make the
"filename" parameter optional. But this is a compatible change, I think.

Also, when returning the image via fd, we could offload its writing to
a bh. This would give us a poor man's async support, where the biggest
drawback would the lack of error detection (can this operation fail anyway?).