[alsa-devel] Status of snd_pcm_rewind()

[Takashi Iwai]

At Mon, 7 Jan 2008 16:14:58 +0100,
Lennart Poettering wrote:
> 
> On Mon, 07.01.08 15:06, Takashi Iwai (tiwai at suse.de) wrote:
> 
> > 
> > At Sat, 22 Dec 2007 19:33:01 +0100,
> > Lennart Poettering wrote:
> > > 
> > > Hi!
> > > 
> > > What's the status of snd_pcm_rewind()? Is it available on all devices?
> > 
> > It should work on all "hw" PCM, but not via every plugin.  The
> > functionality is basically in the PCM core level, independent from
> > the lowlevel driver implementation.
> > 
> > dmix and dshare don't work (unimplemented).  The other plugins should
> > work, though.
> > 
> > > I assume not (at least dmix doesn't...). But I guess I can safely
> > > assume it is available when mmap is used? Is there any API function to
> > > test if it is available?
> > 
> > No, unfortunately.  A self-test?
> 
> Ii assume th "No" is a response to the question if there was any API
> function to test whether it is available, right?

Right.

> What's the answer to the question that I can safely assume that it is
> available when mmap is used?

If I understand correctly -- mmap of the "hw" PCM, then yes, it's
always supported.  (Note that you can still do mmap-alike over any
plugins)

> May I suggest adding an API function that can be used to detect
> whether _rewind() functionality is available?

Adding it would be easy, but I'm a bit worrying about blindly
addition.  Implementing rewind on dmix would be a better option, but
it seems difficult because of its design...


Takashi