v4l2src zerocopy patch

[Stefan Kost <ensonic hora-obscura de>]

hi,

I am working on a patch to enable zerocopy in v4l2src. That is it would
enqueue picture from e.g. xvimagesink and capture into those. This works
already on my embedded device and lowers the CPU for xv4lsrc !
xvimagesink from 15% to 6-7% :-)

The patch is attached to
http://bugzilla.gnome.org/show_bug.cgi?id=583890 (against
gst-plugins-good git).
The patch seems to not break anything so far, but unfortunately not many
drivers support the new behaviour (it will detect it and fallback to
mmap'ed buffers that it uses now). The gspca driver seems to have
support for it. If someone has a camera that uses that driver, it would
rock if you could test the patch.

Stefan