Re: IO plugin and multiple poll descriptors

[Takashi Iwai <tiwai@suse.de>]

At Tue, 17 May 2005 18:15:24 +0200,
I wrote:
> 
> At Tue, 17 May 2005 15:03:35 +0200,
> Marcel Holtmann wrote:
> > 
> > Hi Takashi,
> > 
> > > > for the IO plugin we can specify one descriptor for poll().
> > > > 
> > > > 	io.poll_fd = fd;
> > > > 	io.poll_events = POLLIN;
> > > > 
> > > > I like to use more than one, because in the Bluetooth cases I always
> > > > have to deal with a signal and a separate media channel. Is it possible
> > > > to add support for that or do I must work around it.
> > > 
> > > Currently, the alsa-lib handles only one poll_fd internally although
> > > API allows the multiple poll_fds.  So, it's not quite easy to add the
> > > multiple fds...
> > 
> > are there any plans to change this in the future?
> > 
> > Maybe it is a good idea to retrieve the poll_fd through a callback. I
> > think of something like you already do in the library:
> > 
> > 	poll_descriptors(snd_pcm_ioplug_t *io, struct pollfd *pfds)
> > 	poll_descriptors_count(snd_pcm_ioplug_t *io)
> > 
> > Or do you have a good idea on how to workaround it?
> 
> I agree, adding the appropriate new callbacks would be the simplest
> solution.  I'll implement it soon if no one is against it.

I added the new callbacks to CVS.
The following two fields are added to snd_pcm_ioplug_callback_t:

	/**
	 * poll descriptors count; optional
	 */
	int (*poll_descriptors_count)(snd_pcm_ioplug_t *io);
	/**
	 * poll descriptors; optional
	 */
	int (*poll_descriptors)(snd_pcm_ioplug_t *io, struct pollfd *pfd, unsigned int space);

If they are NULL, poll_fd is used as well as in the former version.

This change breaks the compatibility with older versions.
For the future compatibility, I added a new field to
snd_pcm_ioplug_t.

The first field of snd_pcm_ioplug_t is "version" now.  This field must
be filled by the caller with SND_PCM_IOPLUG_VERSION constant defined
in pcm_ioplug.h.

struct snd_pcm_ioplug {
	/**
	 * protocol version; SND_PCM_IOPLUG_VERSION must be filled here
	 * before calling #snd_pcm_ioplug_create()
	 */
	unsigned int version;
	/**
	 * name of this plugin; must be filled before calling #snd_pcm_ioplug_create()
	 */
	const char *name;
	...

Could you change your driver to follow this?

Any comments appreciated.


Takashi


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