[gstreamer-bugs] [Bug 480557] Nasty segfault in CVS HEAD

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | don't know | Ver: HEAD CVS




------- Comment #10 from Edgard Lima  2007-11-14 16:14 UTC -------

Ok, the commit I pointed out above was really ugly.

Lets have a look at the real bug we are facing (which is a bug in device driver
side):

gst_v4l2src_grab_frame {
...
while (ioctl (v4l2src->v4l2object->video_fd, VIDIOC_DQBUF, &buffer) < 0)

It should never return true unless really there is a buffer available

What happens to my device driver (pwc: Logitech QuickCam Orbit/Sphere USB
webcam) is that when this function is called on third time, we have the
following situation:
buffer[0] is in use upstream
buffer[1] is free ('cause for this buffer, the last one, we always copied)

then the 'ioctl' above returns 0 with buffer.index = 0. which should be
impossible  'cause the buffer[0] has not been finalized yet (so not available
for the driver to write in it yet - means VIDIOC_QBUF not called yet for this
buffer)

So, we have two options

1- doesn't change anything (just rollback my last ugly commit) and report or
send a patch to the device driver guys
2- make always copy for the time being

(I vote 1)

btw: Wim what do you think of make the default buffer pool size 4 instead
current 2?


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