xref: /freebsd/share/man/man4/sndstat.4 (revision ffc4f93e960d38b6f70d59409127f7562e40f916)

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.Dd April 15, 2021
.Dt SNDSTAT 4
.Os
.Sh NAME
.Nm sndstat
.Nd "nvlist-based PCM audio device enumeration interface"
.Sh SYNOPSIS
To compile the driver into the kernel,
place the following lines in the
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device sound"
.Ed
.Sh DESCRIPTION
The ioctl interface provided by
.Pa /dev/sndstat
device allows callers to enumerate PCM audio devices available for use.
In other words, it provides means to get the list of all audio devices
available to the system.
.Sh IOCTLS
For ioctl calls that take an argument, the following structure is used:
.Bd -literal -offset indent
struct sndstioc_nv_arg {
	size_t nbytes;
	void *buf;
};
.Ed
.Pp
Here is an example of an nvlist object with explanations of the common fields:
.Bd -literal -offset indent
dsps (NVLIST ARRAY): 1
    from_user (BOOL): FALSE
    nameunit (STRING): [pcm0]
    devnode (STRING): [dsp0]
    desc (STRING): [Generic (0x8086) (Analog Line-out)]
    pchan (NUMBER): 1 (1) (0x1)
    rchan (NUMBER): 0 (0) (0x0)
    info_play (NVLIST):
        min_rate (NUMBER): 48000 (48000) (0xbb80)
        max_rate (NUMBER): 48000 (48000) (0xbb80)
        formats (NUMBER): 16 (16) (0x10)
        min_chn (NUMBER): 2 (2) (0x2)
        max_chn (NUMBER): 2 (2) (0x2)
    provider_info (NVLIST):
        unit (NUMBER): 0 (0) (0x0)
        bitperfect (BOOL): FALSE
        pvchan (NUMBER): 1 (1) (0x1)
        rvchan (NUMBER): 0 (0) (0x0)
    provider (STRING): [sound(4)]
    ,
.Ed
.Bl -tag -width ".Dv provider_info"
.It Dv from_user
Whether the PCM audio device node is created by in-kernel audio subsystem or
userspace providers.
.It Dv nameunit
The device identification in the form of subsystem plus a unit number.
.It Dv devnode
The PCM audio device node relative path in devfs.
.It Dv desc
The description of the PCM audio device.
.It Dv pchan
The number of playback channels supported by hardware.
This can be 0 if this PCM audio device does not support playback at all.
.It Dv rchan
The number of recording channels supported by hardware.
This can be 0 if this PCM audio device does not support recording at all.
.It Dv info_play
Supported configurations in playback direction.
This exists only if this PCM audio device supports playback.
There are a number of name/value pairs inside this field:
.Bl -tag -width ".Dv min_rate"
.It Dv min_rate
Minimum supported sampling rate.
.It Dv max_rate
Maximum supported sampling rate.
.It Dv formats
Supported sample formats.
.It Dv min_chn
Minimum supported number of channels in channel layout
.It Dv max_chn
Maximum supported number of channels in channel layout
.El
.It Dv info_rec
Supported configurations in recording direction.
This exists only if this PCM audio device supports recording.
There are a number of name/value pairs inside this field:
.Bl -tag -width ".Dv min_rate"
.It Dv min_rate
Minimum supported sampling rate.
.It Dv max_rate
Maximum supported sampling rate.
.It Dv formats
Supported sample formats.
.It Dv min_chn
Minimum supported number of channels in channel layout
.It Dv max_chn
Maximum supported number of channels in channel layout
.El
.It Dv provider_info
Provider-specific fields.
This field may not exist if the PCM audio device is not provided by in-kernel
interface.
This field will not exist if the provider field is an empty string.
.It Dv provider
A string specifying the provider of the PCm audio device.
.El
.Pp
The following ioctls are provided for use:
.Bl -tag -width ".Dv SNDSTIOC_FLUSH_USER_DEVS"
.It Dv SNDSTIOC_REFRESH_DEVS
Drop any previously fetched PCM audio devices list snapshots.
This ioctl takes no arguments.
.It Dv SNDSTIOC_GET_DEVS
Generate and/or return PCM audio devices list snapshots to callers.
This ioctl takes a pointer to
.Fa struct sndstioc_nv_arg
as the first and the only argument.
Callers need to provide a sufficiently large buffer to hold a serialized
nvlist.
If there is no existing PCM audio device list snapshot available in the
internal structure of the opened sndstat.
.Fa fd ,
a new PCM audio device list snapshot will be automatically generated.
Callers have to set
.Fa nbytes
to either 0 or the size of buffer provided.
In case
.Fa nbytes
is 0, the buffer size required to hold a serialized nvlist
stream of current snapshot will be returned in
.Fa nbytes ,
and
.Fa buf
will be ignored.
Otherwise, if the buffer is not sufficiently large,
the ioctl returns success, and
.Fa nbytes
will be set to 0.
If the buffer provided is sufficiently large,
.Fa nbytes
will be set to the size of the serialized nvlist written to the provided buffer.
Once a PCM audio device list snapshot is returned to user-space successfully,
the snapshot stored in the subsystem's internal structure of the given
.Fa fd
will be freed.
.It Dv SNDSTIOC_ADD_USER_DEVS
Add a list of PCM audio devices provided by callers to
.Pa /dev/sndstat
device.
This ioctl takes a pointer to
.Fa struct sndstioc_nv_arg
as the first and the only argument.
Callers have to provide a buffer holding a serialized nvlist.
.Fa nbytes
should be set to the length in bytes of the serialized nvlist.
.Fa buf
should be pointed to a buffer storing the serialized nvlist.
Userspace-backed PCM audio device nodes should be listed inside the serialized
nvlist.
.It Dv SNDSTIOC_FLUSH_USER_DEVS
Flush any PCM audio devices previously added by callers.
This ioctl takes no arguments.
.El
.Sh FILES
.Bl -tag -width ".Pa /dev/sndstat" -compact
.It Pa /dev/sndstat
.El
.Sh EXAMPLES
The following code enumerates all available PCM audio devices:
.Bd -literal -offset indent
#include <sys/types.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/nv.h>
#include <sys/sndstat.h>
#include <sysexits.h>
#include <unistd.h>

int
main()
{
	int fd;
	struct sndstioc_nv_arg arg;
	const nvlist_t * const *di;
	size_t i, nitems;
	nvlist_t *nvl;

	/* Open sndstat node in read-only first */
	fd = open("/dev/sndstat", O_RDONLY);

	if (ioctl(fd, SNDSTIOC_REFRESH_DEVS, NULL))
		err(1, "ioctl(fd, SNDSTIOC_REFRESH_DEVS, NULL)");

	/* Get the size of snapshot, when nbytes = 0 */
	arg.nbytes = 0;
	arg.buf = NULL;
	if (ioctl(fd, SNDSTIOC_GET_DEVS, &arg))
		err(1, "ioctl(fd, SNDSTIOC_GET_DEVS, &arg)");

	/* Get snapshot data */
	arg.buf = malloc(arg.nbytes);
	if (arg.buf == NULL)
		err(EX_OSERR, "malloc");
	if (ioctl(fd, SNDSTIOC_GET_DEVS, &arg))
		err(1, "ioctl(fd, SNDSTIOC_GET_DEVS, &arg)");

	/* Deserialize the nvlist stream */
	nvl = nvlist_unpack(arg.buf, arg.nbytes, 0);
	free(arg.buf);

	/* Get DSPs array */
	di = nvlist_get_nvlist_array(nvl, SNDST_DSPS, &nitems);
	for (i = 0; i < nitems; i++) {
		const char *nameunit, *devnode, *desc;

		/*
		 * Examine each device nvlist item
		 */

		nameunit = nvlist_get_string(di[i], SNDST_DSPS_NAMEUNIT);
		devnode = nvlist_get_string(di[i], SNDST_DSPS_DEVNODE);
		desc = nvlist_get_string(di[i], SNDST_DSPS_DESC);
		printf("Name unit: `%s`, Device node: `%s`, Description: `%s`\n",
		    nameunit, devnode, desc);
	}

	nvlist_destroy(nvl);
	return (0);
}
.Ed
.Sh SEE ALSO
.Xr sound 4 ,
.Xr nv 9
.Sh HISTORY
The nvlist-based ioctls support for
.Nm
device first appeared in
.Fx 13.0 .
.Sh AUTHORS
This manual page was written by
.An Ka Ho Ng Aq Mt khng@FreeBSD.org .