The "alsactl init" rules are read from the files located in the
/usr/share/alsa/init/*. The top level configuration file is
/usr/share/alsa/init/00main. Every line in the rules file contains at least
one key value pair. There are two kind of keys, match and assignment keys. If
all match keys are matching against its value, the rule gets applied and the
assign keys get the specified value assigned.
A rule may consists of a list of one or more key value pairs
separated by a comma. Each key has a distinct operation, depending on the
used operator. Valid operators are:
==
Compare for equality.
!=
Compare for non-equality.
=
Assign a value to a key. Keys that represent a list, are
reset and only this single value is assigned.
+=
Add the value to a key that holds a list of
entries.
:=
Assign a value to a key finally; disallow any later
changes, which may be used to prevent changes by any later rules.
The following key names can be used to match against device
properties:
CARDINDEX
Match the card index of the ALSA driver.
CTL{attribute}
Set or test universal control attribute. Possible
attributes:
numid
Numeric control identification.
iface, interface
Control interface name (CARD, HWEDEP, MIXER, PCM,
RAWMIDI, TIMER, SEQUENCER)
subdev, subdevice
Subdevice number.
name
Control name
index
Control index
type
Control type (BOOLEAN, INTEGER, INTEGER64, ENUMERATED,
BYTES, IEC958)
attr, attribute
Attributes (stored in a string - use match characters *
and ?):
r
control is readable
w
control is writable
v
control is volatile
i
control is inactive
l
control is locked
R
control is TLV readable
W
control is TLV writable
C
control is TLV commandable
o
process is owner of this control
u
control created in user space
owner
Control owner process PID number
count
Control count of values
min
Value range - minimum value
max
Value range - maximum value
step
Value range - step value
dBmin
Value range - minimum dB value
dBmax
Value range - maximum dB value
items
Enumerated value - number of text items
enums
Enumerated value - list of text names stored between '|'
character
value
Value of control stored to a string delimited by comma
(,).
do_search
Search for a control. Value "1" is returned if
a control was found. The CTL{name} key might contain match characters * and ?.
An control index might be specified as first argument starting from zero (e.g.
CTL{do_search 2}="1").
do_count
Search for a controls and return total count of matched
ones. The CTL{name} key might contain match characters * and ?.
CONFIG{sysfs_device}
The relative path to sysfs subsystem specifying the root
directory of a soundcard device. Usually, it should be set to
"/class/sound/card$cardinfo{card}/device".
ATTR{filename}
Match sysfs attribute values of the soundcard device. The
relative path to sysfs tree must be defined by CONFIG{sysfs_device} key.
Trailing whitespace in the attribute values is ignored, if the specified match
value does not contain trailing whitespace itself. Depending on the type of
operator, this key is also used to set the value of a sysfs attribute.
ENV{key}
Match against the value of an environment variable. Up to
five ENV keys can be specified per rule. Depending on the type of
operator, this key is also used to export a variable to the environment.
PROGRAM
Execute external program. The key is true, if the program
returns without exit code zero. The whole event environment is available to
the executed program. The program's output printed to stdout is available for
the RESULT key.
Several buildin commands are available:
__ctl_search
Search for a control. The CTL{name} key might contain
match characters * and ?. An control index might be specified as first
argument starting from zero (e.g. PROGRAM="__ctl_search 2").
__ctl_count
Search for a controls and return total count of matched
ones. The CTL{name} key might contain match characters * and ?.
RESULT
Match the returned string of the last PROGRAM call. This
key can be used in the same or in any later rule after a PROGRAM call.
Most of the fields support a shell style pattern matching. The
following pattern characters are supported:
*
Matches zero, or any number of characters.
?
Matches any single character.
[]
Matches any single character specified within the
brackets. For example, the pattern string 'tty[SR]' would match either 'ttyS'
or 'ttyR'. Ranges are also supported within this match with the '-' character.
For example, to match on the range of all digits, the pattern [0-9] would be
used. If the first character following the '[' is a '!', any characters not
enclosed are matched.
The following keys can get values assigned:
CTL{numid}, CTL{iface}, CTL{device},
CTL{subdev}, CTL{name}, CTL{index},
Select universal control element.
CTL{value}
Value is set (written) also to soundcard's control device
and RESULT key is set to errno code. The result of set operation is always
true (it means continue with next key on line).
CTL{values}
Value is set (written) also to soundcard's control device
(all control values are set to specified value) and RESULT key is set to errno
code. The result of set operation is always true (it means continue with next
key on line).
CTL{write}
Value is set (written) also to soundcard's control device
(all control values are set to specified value). The result of set operation
is true when operation succeed (it means continue with next key on
line).
ENV{key}
Export a variable to the environment. Depending on the
type of operator, this key is also to match against an environment
variable.
RESULT
Set RESULT variable. Note that PROGRAM also sets this
variable, but setting this variable manually might be useful to change code
execution order (included files).
LABEL
Named label where a GOTO can jump to.
GOTO
Jumps to the next LABEL with a matching name. The goto
cannot jump backward.
INCLUDE
Include the specified filename or files in specified
directory.
When a directory is specified, only the files with the extension
".conf" are read. Also they are read in the alphabetical order.
Thus it's highly recommended to use some number prefix (e.g.
"01-something.conf") to assure the order of execucions.
ACCESS
Check if specified file or directory exists
CONFIG{sysfs_device}
The relative path to sysfs subsystem specifying the root
directory of a soundcard device. Usually, it should be set to
"/class/sound/card$cardinfo{card}/device".
PRINT
PRINT value to stdout.
ERROR
PRINT value to stderr.
EXIT
Exit immediately and set program exit code to value
(should be integer). If value is "return" string, parser leaves
current included file and returns to parent configuration file.
The PROGRAM, RESULT, CTL{value},
PRINT, ERROR, EXIT, CONFIG{} fields support
simple printf-like string substitutions. It allows the use of the complete
environment set by earlier matching rules. For all other fields,
substitutions are applied while the individual rule is being processed. The
available substitutions are:
$cardinfo{attribute},
%i{ attribute}
See CARDINFO{} for more details.
$ctl{attribute},
%C{attribute}
See CTL{} for more details.
$attr{file},
%s{file}
The value of a sysfs attribute found at the device, where
all keys of the rule have matched. If the attribute is a symlink, the last
element of the symlink target is returned as the value.
$env{key},
%E{key}
The value of an environment variable.
$result, %c
The string returned by the external program requested
with PROGRAM. A single part of the string, separated by a space character may
be selected by specifying the part number as an attribute: %c{N}. If
the number is followed by the '+' char this part plus all remaining parts of
the result string are substituted: %c{N+}
$sysfsroot, %r
Root directory where sysfs file-system is mounted.
Ususally, this value is just "/sys".
$config{key},
%g{key}
The value of a configuration variable. See CONFIG{} for
more details.
%%
The '%' character itself.
$$
The '$' character itself.
The count of characters to be substituted may be limited by
specifying the format length value. For example, '%3s{file}' will only
insert the first three characters of the sysfs attribute
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