Re: [linux-dvb] Help using DMX_SET_BUFFER_SIZE
[EMAIL PROTECTED] wrote: > > > Possible solutions: > > 2) enable the resize of a live ring buffer. > Currently: > > dvb_dvr_write DOES lock the mutex (dmxdev->mutex) > dvb_dvr_read DOES NOT lock the mutex (the code to lock the mutex is there, > but commented out, why?) > > Is it enough to lock the mutex in dvb_dvr_read? No, it isn't! dvb_dmxdev_ts_callback is the function writing in the dvr_buffer, not dvb_dvr_write (which must be a system call I think). Things get more complicated... I've understood that a callback function cannot sleep, so a mutex must not be used. And a relocation of the buffer counts as reading and writing. > Then the new function to change the buffer size could just lock the mutex, > change the size and unlock. How many readers of the dvr can there be? It looks like only 1 (otherwise the mutex would not be commented out). Is it legal to write an application that reads dvr from one thread/process, and calls other ioctl from an other? I guess not, for the same reason why it cannot read from 2 threads. So, if the above is true, I only need to synchronize with dvb_dmxdev_ts_callback, i.e. acquire the same spin_lock. Does it make sense? PS: It seems that I am replying my own emails... and I do that while I discover and understand more about the architecture of the dvr/demux. What is a good starting point to get an idea about all those synchronization issues? My next reading is the "Unreliable Guide To Locking". More to follow... ___ linux-dvb mailing list linux-dvb@linuxtv.org http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
Re: [linux-dvb] Help using DMX_SET_BUFFER_SIZE
Florian Lohoff wrote:
> On Sat, Mar 01, 2008 at 12:20:05AM +, Andrea wrote:
>
> In 2.6.25-rc3 the dvr kernel side looks like this:
>
> 1015 switch (cmd) {
> 1016 case DMX_SET_BUFFER_SIZE:
> 1017 // FIXME: implement
> 1018 ret = 0;
> 1019 break;
>
> i guess its clear why it doesnt make a difference ;)
I've been thinking a little about how to implement that and I came across this
issue:
(given my limited experience of dvb kernel developing the following might not
be 100% correct...)
Usually everything (frontend, demux) is set up and only afterwards a dvr is
opened.
That means that a dvr is live immediately and its buffer gets filled
immediately.
So it is a bit tricky to change the size of the buffer while the buffer is
operating.
The demux on the other hand does not operate immediately.
Possible solutions:
1) open the DVR before starting the demux. So that it is possible to change the
dvr buffer size
it is usually done the other way round.
2) enable the resize of a live ring buffer.
Currently:
dvb_dvr_write DOES lock the mutex (dmxdev->mutex)
dvb_dvr_read DOES NOT lock the mutex (the code to lock the mutex is there, but
commented out, why?)
Is it enough to lock the mutex in dvb_dvr_read?
Then the new function to change the buffer size could just lock the mutex,
change the size and unlock.
3) don't bother.
I personally prefer option 2), which gives me the chance to learn how all that
works.
I'd like to have an opinion about this matter, maybe just to improve my
knowledge of the dvb mechanism.
Anyone?
___
linux-dvb mailing list
linux-dvb@linuxtv.org
http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
Re: [linux-dvb] Help using DMX_SET_BUFFER_SIZE
Florian Lohoff wrote:
> On Sat, Mar 01, 2008 at 12:20:05AM +, Andrea wrote:
>> 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).
>
> In 2.6.25-rc3 the dvr kernel side looks like this:
>
> 1015 switch (cmd) {
> 1016 case DMX_SET_BUFFER_SIZE:
> 1017 // FIXME: implement
> 1018 ret = 0;
> 1019 break;
>
> i guess its clear why it doesnt make a difference ;)
>
> Flo
Yes I had noticed that and I was trying to see what I can do.
My problem is that I replace the // FIXME with a printk() and it does not get
called
How is it supposed to work?
I open /dev/dvb/adapter0/dvr0, I get back a file descriptor and the I call the
ioctl with that file
descriptor.
This code comes from gnutv_data.c plus my additional code
// open dvr device
dvrfd = dvbdemux_open_dvr(adapter_id, 0, 1, 0);
if (dvrfd < 0) {
fprintf(stderr, "Failed to open DVR device\n");
exit(1);
}
if (buffer_size > 0)
{
int res = dvbdemux_set_buffer(dvrfd, buffer_size);
if (res < 0) {
fprintf(stderr, "Failed to set ring buffer size\n");
exit(1);
}
}
Regardless of what is implemented or not, would that be correct?
Andrea
___
linux-dvb mailing list
linux-dvb@linuxtv.org
http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
Re: [linux-dvb] Help using DMX_SET_BUFFER_SIZE
On Sat, Mar 01, 2008 at 12:20:05AM +, Andrea wrote:
> 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).
In 2.6.25-rc3 the dvr kernel side looks like this:
1015 switch (cmd) {
1016 case DMX_SET_BUFFER_SIZE:
1017 // FIXME: implement
1018 ret = 0;
1019 break;
i guess its clear why it doesnt make a difference ;)
Flo
--
Florian Lohoff [EMAIL PROTECTED] +49-171-2280134
Those who would give up a little freedom to get a little
security shall soon have neither - Benjamin Franklin
signature.asc
Description: Digital signature
___
linux-dvb mailing list
linux-dvb@linuxtv.org
http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
