src/lib/libsndio/sioctl_open.3

.\" $OpenBSD: sioctl_open.3,v 1.13 2022/05/03 13:03:30 ratchov Exp $
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.\" Copyright (c) 2011-2020 Alexandre Ratchov <alex@caoua.org>
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.Dd $Mdocdate: May 3 2022 $
.Dt SIOCTL_OPEN 3
.Os
.Sh NAME
.Nm sioctl_open ,
.Nm sioctl_close ,
.Nm sioctl_ondesc ,
.Nm sioctl_onval ,
.Nm sioctl_setval ,
.Nm sioctl_nfds ,
.Nm sioctl_pollfd ,
.Nm sioctl_eof
.Nd interface to audio parameters
.Sh SYNOPSIS
.Fd #include <sndio.h>
.Ft struct sioctl_hdl *
.Fo sioctl_open
.Fa "const char *name"
.Fa "unsigned int mode"
.Fa "int nbio_flag"
.Fc
.Ft void
.Fo sioctl_close
.Fa "struct sioctl_hdl *hdl"
.Fc
.Ft int
.Fo sioctl_ondesc
.Fa "struct sioctl_hdl *hdl"
.Fa "void (*cb)(void *arg, struct sioctl_desc *desc, int val)"
.Fa "void *arg"
.Fc
.Ft int
.Fo sioctl_onval
.Fa "struct sioctl_hdl *hdl"
.Fa "void (*cb)(void *arg, unsigned int addr, unsigned int val)"
.Fa "void *arg"
.Fc
.Ft int
.Fo sioctl_setval
.Fa "struct sioctl_hdl *hdl"
.Fa "unsigned int addr"
.Fa "unsigned int val"
.Fc
.Ft int
.Fo sioctl_nfds
.Fa "struct sioctl_hdl *hdl"
.Fc
.Ft int
.Fo sioctl_pollfd
.Fa "struct sioctl_hdl *hdl"
.Fa "struct pollfd *pfd"
.Fa "int events"
.Fc
.Ft int
.Fo sioctl_revents
.Fa "struct sioctl_hdl *hdl"
.Fa "struct pollfd *pfd"
.Fc
.Ft int
.Fo sioctl_eof
.Fa "struct sioctl_hdl *hdl"
.Fc
.Sh DESCRIPTION
Audio devices may expose a number of controls, like the playback volume control.
Each control has an integer
.Em address
and an integer
.Em value .
Some values are boolean and can only be switched to either 0 (off) or 1 (on).
Any control may be changed by submitting
a new value to its address.
When values change, asynchronous notifications are sent.
.Pp
Control descriptions are available, allowing them to be grouped and
represented in a human readable form.
.Ss Opening and closing the control device
First the application must call the
.Fn sioctl_open
function to obtain a handle
that will be passed as the
.Fa hdl
argument to other functions.
.Pp
The
.Fa name
parameter gives the device string discussed in
.Xr sndio 7 .
In most cases it should be set to SIO_DEVANY to allow
the user to select it using the
.Ev AUDIODEVICE
environment variable.
The
.Fa mode
parameter is a bitmap of the
.Dv SIOCTL_READ
and
.Dv SIOCTL_WRITE
constants indicating whether control values can be read and
modified respectively.
.Pp
If the
.Fa nbio_flag
argument is 1, then the
.Fn sioctl_setval
function (see below) may fail instead of blocking and
the
.Fn sioctl_ondesc
function doesn't block.
.Pp
The
.Fn sioctl_close
function closes the control device and frees any allocated resources
associated with the handle.
.Ss Control descriptions
The
.Fn sioctl_ondesc
function can be used to obtain the description of all available controls
and their initial values.
It registers a callback function that is immediately invoked for all
controls.
It is called once with a
.Dv NULL
argument to indicate that the full
description was sent and that the caller has a consistent
representation of the control set.
.Pp
Then, whenever a control description changes, the callback is
invoked with the updated information followed by a call with a
.Dv NULL
argument.
.Pp
Controls are described by the
.Vt sioctl_desc
structure as follows:
.Bd -literal
struct sioctl_node {
	char name[SIOCTL_NAMEMAX];	/* ex. "spkr" */
	int unit;			/* optional number or -1 */
};

struct sioctl_desc {
	unsigned int addr;		/* control address */
#define SIOCTL_NONE		0	/* deleted */
#define SIOCTL_NUM		2	/* integer in the maxval range */
#define SIOCTL_SW		3	/* on/off switch (1 or 0) */
#define SIOCTL_VEC		4	/* number, element of vector */
#define SIOCTL_LIST		5	/* switch, element of a list */
#define SIOCTL_SEL		6	/* element of a selector */
	unsigned int type;		/* one of above */
	char func[SIOCTL_NAMEMAX];	/* function name, ex. "level" */
	char group[SIOCTL_NAMEMAX];	/* group this control belongs to */
	struct sioctl_node node0;	/* affected node */
	struct sioctl_node node1;	/* dito for SIOCTL_{VEC,LIST,SEL} */
	unsigned int maxval;		/* max value */
};
.Ed
.Pp
The
.Fa addr
attribute is the control address, usable with
.Fn sioctl_setval
to set its value.
.Pp
The
.Fa type
attribute indicates what the structure describes.
Possible types are:
.Bl -tag -width "SIOCTL_LIST"
.It Dv SIOCTL_NONE
A previously valid control was deleted.
.It Dv SIOCTL_NUM
An integer control in the range from 0 to
.Fa maxval ,
inclusive.
For instance the volume of the speaker.
.It Dv SIOCTL_SW
A boolean control.
For instance the switch to mute the speaker.
.It Dv SIOCTL_VEC
Element of an array of integer controls.
For instance the knob to control the amount of signal flowing
from the line input to the speaker.
.It Dv SIOCTL_LIST
An element of an array of boolean switches.
For instance the line-in position of the
speaker source selector.
.It Dv SIOCTL_SEL
Same as
.Dv SIOCTL_LIST
but exactly one element is selected at a time.
.El
.Pp
The
.Fa func
attribute is the name of the parameter being controlled.
There may be no parameters of different types with the same name.
.Pp
The
.Fa node0
and
.Fa node1
attributes indicate the names of the controlled nodes, typically
channels of audio streams.
.Fa node1
is meaningful for
.Dv SIOCTL_VEC ,
.Dv SIOCTL_LIST ,
and
.Dv SIOCTL_SEL
only.
.Pp
Names in the
.Fa node0
and
.Fa node1
attributes and
.Fa func
are strings usable as unique identifiers within the given
.Fa group .
.Pp
The
.Fa maxval
attribute indicates the maximum value of this control.
For boolean control types it is set to 1.
.Ss Changing and reading control values
Controls are changed with the
.Fn sioctl_setval
function, by giving the index of the control and the new value.
The
.Fn sioctl_onval
function can be used to register a callback which will be invoked whenever
a control changes.
Integer values are in the range from 0 to
.Fa maxval .
.Ss Interface to poll(2)
The
.Fn sioctl_pollfd
function fills the array
.Fa pfd
of
.Vt pollfd
structures, used by
.Xr poll 2 ,
with
.Fa events ;
the latter is a bit-mask of
.Dv POLLIN
and
.Dv POLLOUT
constants.
.Fn sioctl_pollfd
returns the number of
.Vt pollfd
structures filled.
The
.Fn sioctl_revents
function returns the bit-mask set by
.Xr poll 2
in the
.Fa pfd
array of
.Vt pollfd
structures.
If
.Dv POLLOUT
is set,
.Fn sioctl_setval
can be called without blocking.
.Dv POLLHUP
may be set if an error occurs, even if it is not selected with
.Fn sioctl_pollfd .
.Dv POLLIN
is not used yet.
.Pp
The
.Fn sioctl_nfds
function returns the number of
.Vt pollfd
structures the caller must preallocate in order to be sure
that
.Fn sioctl_pollfd
will never overrun.
.Sh ENVIRONMENT
.Bl -tag -width AUDIODEVICE
.It Ev AUDIODEVICE
The default
.Xr sndio 7
device used by
.Fn sioctl_open .
.El
.Sh SEE ALSO
.Xr sndioctl 1 ,
.Xr poll 2 ,
.Xr sio_open 3 ,
.Xr sndio 7
.Sh HISTORY
These functions first appeared in
.Ox 6.7 .
.Sh AUTHORS
.An Alexandre Ratchov Aq Mt ratchov@openbsd.org