[alsa-devel] Confusion about whether snd_pcm_poll_descriptors_revents()'s revents field is a single integer or an array

[Takashi Iwai]

At Mon, 2 Feb 2009 16:02:38 +0100 (CET),
Jaroslav Kysela wrote:
> 
> On Mon, 2 Feb 2009, Takashi Iwai wrote:
> 
> > At Mon, 2 Feb 2009 15:49:13 +0100,
> > Lennart Poettering wrote:
> > > 
> > > On Mon, 02.02.09 08:02, Takashi Iwai (tiwai at suse.de) wrote:
> > > 
> > > > > If we look into the pcm example how snd_pcm_poll_descriptors_revents()
> > > > > is used then we can see that the revents parameter apparently is
> > > > > supposed to be a single integer. (which makes a lot of sense to me)
> > > > > 
> > > > > http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html#a33
> > > > > 
> > > > > However, snd_pcm_wait_nocheck() calls the same function and assumes it
> > > > > is a complete array!
> > > > > 
> > > > > http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/pcm/pcm.c;h=74d1d1a4bd6083cd461b6d793c0ae41cca912f16;hb=HEAD#l2368
> > > > > 
> > > > > So what's it now? It makes more sense to me if it would be a single
> > > > > fd. 
> > > > 
> > > > No, it's a bug in test/pcm.c.  As documented, the API converts (fixes)
> > > > each poll_fd in the given array.
> > > 
> > > But does that really make sense? I mean
> > > snd_pcm_poll_descriptors_revents() is supposed to be called by
> > > applications that integrate ALSA into some kind of event loop. What
> > > are they supposed to do with those multiple entries -- except simply
> > > ORing them together and treating them as one? The application has no
> > > information what those seperate fds mean, so why export that
> > > information to the app?
> > 
> > Originally the multiple pfds were introduced to handle multi plugin,
> > which bundles multiple instances.  So, the original version of it was
> > pretty straightforward -- just simply calls poll to each and update
> > each pfd necessarily.
> 
> But snd_pcm_poll_descriptors_revents() was designed to return single 
> value originally.

Hrm, then the definition was very ambiguous...


Takashi