xref: /freebsd/share/man/man4/sndstat.4 (revision bbca3a75bb412f7106a569b82c616404103be084)

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.Dd June 5, 2024
.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
	rchan (NUMBER): 0
	info_play (NVLIST):
		min_rate (NUMBER): 48000
		max_rate (NUMBER): 48000
		formats (NUMBER): 16
		min_chn (NUMBER): 2
		max_chn (NUMBER): 2
	provider_info (NVLIST):
		unit (NUMBER): 0
		bitperfect (BOOL): FALSE
		pvchan (NUMBER): 1
		rvchan (NUMBER): 0
		channel_info (NVLIST_ARRAY): 1
			name (STRING): pcm0:virtual_play:dsp0.vp0
			parentchan (STRING): pcm0:play:dsp0.p0
			unit (NUMBER): 1
			latency (NUMBER): 2
			rate (NUMBER): 48000
			format (NUMBER): 0x201000
			pid (NUMBER): 1234
			comm (STRING): mpv
			interrupts (NUMBER): 0
			feedcount (NUMBER): 0
			xruns (NUMBER): 0
			left_volume (NUMBER): 45
			right_volume (NUMBER): 45
			hwbuf_fmt (NUMBER): 0x200010
			hwbuf_size (NUMBER): 0
			hwbuf_blksz (NUMBER): 0
			hwbuf_blkcnt (NUMBER): 0
			hwbuf_free (NUMBER): 0
			hwbuf_ready (NUMBER): 0
			swbuf_fmt (NUMBER): 0x201000
			swbuf_size (NUMBER): 16384
			swbuf_blksz (NUMBER): 2048
			swbuf_blkcnt (NUMBER): 8
			swbuf_free (NUMBER): 16384
			swbuf_ready (NUMBER): 0
			feederchain (STRING):
				[userland ->
				feeder_root(0x00201000) ->
				feeder_format(0x00201000 -> 0x00200010) ->
				feeder_volume(0x00200010) -> hardware]
	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.
For the
.Xr sound 4
provider, there are a number of name/value pairs inside this field:
.Bl -tag -width ".Dv channel_info"
.It Dv unit
Sound card unit.
.It Dv bitperfect
Whether the sound card has bit-perfect mode enabled.
.It Dv pvchan
Number of playback virtual channels.
.It Dv rvchan
Number of recording virtual channels.
.It Dv channel_info
Channel information.
There are a number of name/value pairs inside this field:
.Bl -tag -width ".Dv hwbuf_blkcnt"
.It Dv name
Channel name.
.It Dv parenchan
Parent channel name (e.g., in the case of virtual channels).
.It Dv unit
Channel unit.
.It Dv latency
Latency.
.It Dv rate
Sampling rate.
.It Dv format
Sampling format.
.It Dv pid
PID of the process consuming the channel.
.It Dv comm
Name of the process consuming the channel.
.It Dv interrupts
Number of interrupts since the channel has been opened.
.It Dv xruns
Number of overruns/underruns, depending on channel direction.
.It Dv feedcount
Number of read/written bytes since the channel has been opened.
.It Dv left_volume
Left volume.
.It Dv right_volume
Right volume.
.It Dv hwbuf_format
Hardware buffer format.
.It Dv hwbuf_size
Hardware buffer size.
.It Dv hwbuf_blksz
Hardware buffer block size.
.It Dv hwbuf_blkcnt
Hardware buffer block count.
.It Dv hwbuf_free
Free space in hardware buffer (in bytes).
.It Dv hwbuf_ready
Number of bytes ready to be read/written from hardware buffer.
.It Dv swbuf_format
Software buffer format.
.It Dv swbuf_size
Software buffer size.
.It Dv swbuf_blksz
Software buffer block size.
.It Dv swbuf_blkcnt
Software buffer block count.
.It Dv swbuf_free
Free space in software buffer (in bytes).
.It Dv swbuf_ready
Number of bytes ready to be read/written from software buffer.
.It Dv feederchain
Channel feeder chain.
.El
.El
.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 .