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Date: Wed, 14 Mar 2012 10:13:19 -0300
From: Luiz Capitulino <lcapitulino@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH/RFC 0/7] Screendump to UNIX socket & in PNG
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: qemu-devel@nongnu.org, =?ISO-8859-1?B?TWFyYy1BbmRy6Q==?= Lureau <marcandre.lureau@redhat.com>, =?ISO-8859-1?B?TWFyYy1BbmRy6Q==?= Lureau <mlureau@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>, =?ISO-8859-1?B?TWFyYy1BbmRy6Q==?= Lureau <marcandre.lureau@gmail.com>

On Wed, 14 Mar 2012 10:01:15 +0000
Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Wed, Mar 14, 2012 at 9:51 AM, Gerd Hoffmann <kraxel@redhat.com> wrote:
> > =A0Hi,
> >
> >> The most practical first step would be simply sending the ppm over a
> >> socket from ppm_save(). =A0The 'screendump' command today already bloc=
ks
> >> so no new badness is being added. =A0There 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. =A0Or at least have some numbers to see how bad it actually is.
>=20
> 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?=
).