I was debugging a small program of mine and found that:
- when I do a poll after opening the device, and not doing a read first,
it would always give me a POLLERR instead of a POLLIN.
Example:
videofd=open("/dev/video0", O_RDONLY);
// Add video device
poll_item.fd = videofd;
poll_item.events = POLLIN;
poll_item.revents = 0;
// poll infinite
retvalue = poll(&poll_item, 1, -1);
poll_item.revents is allways POLLERR.
When I do a read(videofd, buffer, 0); directly after the open and then
do the poll I get POLLIN.
I can trace this back to the fact that the bit IVTV_F_S_STREAMING is
only set, in function ivtv_v4l2_read in file ivtv-fileops.c, when at
least one read is done. Even if the request is to read 0 (zero) bytes.
I do not know if this is by design.
But I would think that it should be possible to first do a poll to see
if data is available to read before I even do any reading. So probably
the IVTV_F_S_STREAMING bit should be set in the function ivtv_v4l2_open
in file ivtv-fileops.c.
This problem is in ivtv 0.10.0RC1 and I would think even in the earlier
versions.
I did not yet spend time to find a fix because I would first like to
know if this is by design or not.
When I use cat /dev/video0 | xine stdin://mpeg2 I get audio and picture
so the device is allright.
Regards,
Michel.
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