[alsa-devel] dsnoop issues
tiwai at suse.de
Fri Apr 27 15:09:10 CEST 2007
At Fri, 27 Apr 2007 15:00:22 +0200 (CEST),
Jaroslav Kysela wrote:
> On Fri, 27 Apr 2007, Takashi Iwai wrote:
> > At Fri, 27 Apr 2007 13:27:00 +0100,
> > Gordon Miller wrote:
> > >
> > > Hi
> > >
> > > All my snd_pcm_readi calls return too few frames. Also when I switch to
> > > stereo, the sound is muted. I cannot change this by adjusting period &
> > > buffer sizes. dsnoop is enabled by default. The documentation for
> > > snd_pcm_readi says that the only way that the frame count can be short
> > > is because of a signal or xrun. Well this clearly isn't the case.
> > Actually, the documentation is wrong, IMO. The typical behavior of
> > read syscall is that it returns a value actually read by that call.
> > It doesn't guarantee whether the requested size is filled, and can be
> > shorter than requested. As snd_pcm_readi() emulates the read syscall,
> > it should behave in that way.
> I don't think so completely. For blocking mode (!O_NONBLOCK), all possible
> data should be read. Only signal or an error should break this.
> The read logic for dsnoop is in snd_pcm_read_areas() in pcm/pcm.c
In the current implementation, it may work in that way. But, in
general, I'm against such a condition. It's not what read syscalls
does, so there is no real reason that snd_pcm_readi() should do so.
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