Help using DMX_SET_BUFFER_SIZE

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Hi,

I've tried to add an extra argument to gnutv to set the size of the dvb_ringbuffer via 
DMX_SET_BUFFER_SIZE.

I have not really understood the difference between dvr and demux.
It seems that gnutv uses the dvr to read from the DVB card and then copies the content to a file.

I call

int dvbdemux_set_buffer(int fd, int bufsize)
{
	return ioctl(fd, DMX_SET_BUFFER_SIZE, bufsize);
}

on the dvr (I think), but it does not make much of a change. The ioctl call returns success.
I've printed a lot of debug output (adding a few dprintk) and this is what I see when I run gnutv.
Now, I set the buffer to 1024 * 1024 which is nowhere in the log.
I cannot see in the log the 2 functions (demux and dvr) handling this ioctl call:
dvb_demux_do_ioctl and dvb_dvr_do_ioctl (I've added some printk as well).

	printk("function : %s %d\n", __FUNCTION__, cmd);


/sbin/modprobe dvb_core debug=1 dvbdev_debug=1


Feb 29 23:59:34 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:34 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:34 thinkpad kernel: function : dvb_dmxdev_filter_set
Feb 29 23:59:34 thinkpad kernel: function : dvb_dvr_open
Feb 29 23:59:34 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:34 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:34 thinkpad kernel: function : dvb_dmxdev_filter_set
Feb 29 23:59:34 thinkpad kernel: dmxdev: dvb_ringbuffer_init 1925120
Feb 29 23:59:34 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:34 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: dmxdev: section callback 00 b0 25 10 04 c5
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_dmxdev_filter_set
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: dmxdev: section callback 02 b0 82 10 84 c7
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: function : dvb_demux_open
Feb 29 23:59:35 thinkpad kernel: dmxdev: dvb_ringbuffer_init 8192
Feb 29 23:59:35 thinkpad kernel: dmxdev: section callback 00 b0 25 10 04 c5
Feb 29 23:59:35 thinkpad kernel: dmxdev: section callback 02 b0 82 10 84 c7
Feb 29 23:59:35 thinkpad kernel: dmxdev: section callback 00 b0 25 10 04 c5
Feb 29 23:59:35 thinkpad kernel: dmxdev: section callback 02 b0 82 10 84 c7
Feb 29 23:59:35 thinkpad kernel: dmxdev: section callback 00 b0 25 10 04 c5
Feb 29 23:59:35 thinkpad kernel: dmxdev: section callback 02 b0 82 10 84 c7
Feb 29 23:59:36 thinkpad kernel: dmxdev: section callback 70 70 05 d4 fd 23
Feb 29 23:59:36 thinkpad kernel: dmxdev: section callback 00 b0 25 10 04 c5
Feb 29 23:59:36 thinkpad kernel: dmxdev: section callback 02 b0 82 10 84 c7
Feb 29 23:59:36 thinkpad kernel: dmxdev: section callback 00 b0 25 10 04 c5
Feb 29 23:59:36 thinkpad kernel: dmxdev: section callback 02 b0 82 10 84 c7



My questions are

1) how many ringbuffers are there? 2 sizes are reported in the log.
2) in the log it seems the buffer is recreated every time.
3) why can't I see any call to dvb_demux_do_ioctl and dvb_dvr_do_ioctl?
4) ... what is the difference between demux and dvr? :-)

I'm using a Hauppauge WinTV NOVA T USB2, 2.6.24.2, letest mercurial source code.


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