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v4l2: Workaround libv4l2 RW emulation bug

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When libv4l2 emulates RW mode on top of MMAP devices, the queues are
only initialized on first read. The problem is that poll() will fail
if called before the queues are initialized and streaming. Workaround
this by doing a zero size read when pool is started in that IO mode.

https://bugzilla.gnome.org/show_bug.cgi?id=740633
This commit is contained in:
Nicolas Dufresne 2014-12-07 17:33:51 -05:00
parent 0e05faf91a
commit eb1dcd841a
1 changed files with 9 additions and 0 deletions
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9
sys/v4l2/gstv4l2bufferpool.c
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@ -646,6 +646,15 @@ gst_v4l2_buffer_pool_start (GstBufferPool * bpool)
switch (obj->mode) {
case GST_V4L2_IO_RW:
can_allocate = TRUE;
#ifdef HAVE_LIBV4L2
/* This workaround a unfixable bug in libv4l2 when RW is emulated on top
* of MMAP. In this case, the first read initialize the queues, but the
* poll before that will always fail. Doing an empty read, forces the
* queue to be initialized now. We only do this if we have a streaming
* driver. */
if (obj->vcap.capabilities & V4L2_CAP_STREAMING)
v4l2_read (obj->video_fd, NULL, 0);
#endif
break;
case GST_V4L2_IO_DMABUF:
case GST_V4L2_IO_MMAP: