IO plugin and multiple poll descriptors

IO plugin and multiple poll descriptors

[Marcel Holtmann]

Hi guys,

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.

Regards

Marcel




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Re: IO plugin and multiple poll descriptors

[Takashi Iwai]

At Sun, 15 May 2005 18:16:51 +0200,
Marcel Holtmann wrote:
> 
> Hi guys,
> 
> 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...


Takashi


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Re: IO plugin and multiple poll descriptors

[Marcel Holtmann]

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?

Regards

Marcel




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Re: IO plugin and multiple poll descriptors

[Takashi Iwai]

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.


Takashi


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Re: IO plugin and multiple poll descriptors

[Takashi Iwai]

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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Re: IO plugin and multiple poll descriptors

[Marcel Holtmann]

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.

should we set poll_fd to -1 or leave it untouched when using the new
callbacks.

We can set poll_events through the callback now, right? I like to have
different events for different descriptors. One POLLIN and one POLLOUT.

What happens at the moment when I really return two poll_fd.

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

Does it? If the new callbacks are not used you will fall back to poll_fd
and so no difference at all.

And you never released a final version with IOPLUG support.

> 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?

As soon as the anonymous CVS gives me the code ;)

Regards

Marcel




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Re: IO plugin and multiple poll descriptors

[Takashi Iwai]

At Wed, 18 May 2005 14:05:43 +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.
> 
> should we set poll_fd to -1 or leave it untouched when using the new
> callbacks.

It doesn't matter.  If the callback is defined, it's always used.
-1 would be better to catch possible bugs, though.

> We can set poll_events through the callback now, right? I like to have
> different events for different descriptors. One POLLIN and one POLLOUT.

Yes.  The callback has to set poll_events, too.

> What happens at the moment when I really return two poll_fd.
> 
> > This change breaks the compatibility with older versions.
> > For the future compatibility, I added a new field to
> > snd_pcm_ioplug_t.
> 
> Does it? If the new callbacks are not used you will fall back to poll_fd
> and so no difference at all.

Well, I inserted in the middle, not at the end.

> And you never released a final version with IOPLUG support.

Yes.  I don't care the compatibility *now* at all.
But, as I wrote, this is for *future* compatibility.  Once after
1.0.9-final is out, we should be careful about it.


Takashi


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Re: IO plugin and multiple poll descriptors

[Marcel Holtmann]

Hi Takashi,

thanks for the answers.

> > What happens at the moment when I really return two poll_fd.

What about this one?

> > > This change breaks the compatibility with older versions.
> > > For the future compatibility, I added a new field to
> > > snd_pcm_ioplug_t.
> > 
> > Does it? If the new callbacks are not used you will fall back to poll_fd
> > and so no difference at all.
> 
> Well, I inserted in the middle, not at the end.

You are right. I always forget to think about binary compatibility ;)

> > And you never released a final version with IOPLUG support.
> 
> Yes.  I don't care the compatibility *now* at all.
> But, as I wrote, this is for *future* compatibility.  Once after
> 1.0.9-final is out, we should be careful about it.

I agree.

Regards

Marcel




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Re: IO plugin and multiple poll descriptors

[Takashi Iwai]

At Wed, 18 May 2005 14:56:43 +0200,
Marcel Holtmann wrote:
> 
> > > What happens at the moment when I really return two poll_fd.
> 
> What about this one?

The poll_descriptors_count and poll_descriptors should return 2,
for example,

int my_poll_descriptors_count(snd_pcm_ioplug_t *io)
{
	return 2;
}

int my_poll_descriptors(snd_pcm_ioplug_t *io, struct pollfd *pfds,
	unsigned int space)
{
	if (space < 2) {
		error("Too little pfd\n");
		return 0;
	}
	pfds[0].fd = fd0;
	pfds[0].events = POLLOUT | POLLERR | POLLNVAL
	pfds[1].fd = fd1;
	pfds[0].events = POLLIN | POLLERR | POLLNVAL
	return 2;
}


Takashi


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Re: IO plugin and multiple poll descriptors

[Marcel Holtmann]

Hi Takashi,

> > > > What happens at the moment when I really return two poll_fd.
> > 
> > What about this one?
> 
> The poll_descriptors_count and poll_descriptors should return 2,
> for example,
> 
> int my_poll_descriptors_count(snd_pcm_ioplug_t *io)
> {
> 	return 2;
> }
> 
> int my_poll_descriptors(snd_pcm_ioplug_t *io, struct pollfd *pfds,
> 	unsigned int space)
> {
> 	if (space < 2) {
> 		error("Too little pfd\n");
> 		return 0;
> 	}
> 	pfds[0].fd = fd0;
> 	pfds[0].events = POLLOUT | POLLERR | POLLNVAL
> 	pfds[1].fd = fd1;
> 	pfds[0].events = POLLIN | POLLERR | POLLNVAL
> 	return 2;
> }

I know, but what I meant was if both descriptors are handled inside the
library. Previous you said that multiple descriptors are not supported.
Of did I understand that wrong?

Regards

Marcel




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Re: IO plugin and multiple poll descriptors

[Takashi Iwai]

At Wed, 18 May 2005 15:45:11 +0200,
Marcel Holtmann wrote:
> 
> Hi Takashi,
> 
> > > > > What happens at the moment when I really return two poll_fd.
> > > 
> > > What about this one?
> > 
> > The poll_descriptors_count and poll_descriptors should return 2,
> > for example,
> > 
> > int my_poll_descriptors_count(snd_pcm_ioplug_t *io)
> > {
> > 	return 2;
> > }
> > 
> > int my_poll_descriptors(snd_pcm_ioplug_t *io, struct pollfd *pfds,
> > 	unsigned int space)
> > {
> > 	if (space < 2) {
> > 		error("Too little pfd\n");
> > 		return 0;
> > 	}
> > 	pfds[0].fd = fd0;
> > 	pfds[0].events = POLLOUT | POLLERR | POLLNVAL
> > 	pfds[1].fd = fd1;
> > 	pfds[0].events = POLLIN | POLLERR | POLLNVAL
> > 	return 2;
> > }
> 
> I know, but what I meant was if both descriptors are handled inside the
> library. Previous you said that multiple descriptors are not supported.
> Of did I understand that wrong?

Ah, yes I mentioned it.  Don't worry, it was fixed on CVS, too :)


Takashi


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