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Alsa-Hook-Plugin
Object: Provide a Hook on Alsa PCM to check permission again AGL Advance Audio Agent
Status: Release Candidate
Author: Fulup Ar Foll fulup@iot.bzh
Date : August-2017
Functionalities:
- Execute a set of unix/ws RPC request again AGL binders to allow/deny access
- Keep websocket open in an idependant thread in order to monitor event received from AGL audio agent
Installation
- Alsaplugins are typically search in /usr/share/alsa-lib. Nevertheless a full path might be given
- This plugin implement a hook on a slave PCM. Typically this slave PCM is a dedicated virtual channel (eg: navigation, emergency,...)
- Config should be place in ~/.asoundrc (see config sample in PROJECT_ROOT/conf.d/alsa)
Test
- Install a full .asoundrc from conf.d/project/alsa.d
- speaker-test -DMyNavigationHook -c2 -twav
Config
```
#
# Author: Fulup Ar Foll
# Object: PCM hook type
#
# Test : Note: Jabra_USB=hw:v1340
# Check SoundCard ==> speaker-test -Dhw:v1340 -c2 -twav
# Check MixerPCM ==> speaker-test -DSpeakers -c2 -twav
# Check SoftVol ==> speaker-test -DMusicPCM -c2 -twav
# Check Plugin ==> speaker-test -DMultimedia -c2 -twav
# MultiMedia aplay -DDMyNavPCM /usr/share/sounds/alsa/test.wav
#
# Bug/Feature: when softvol control is initialised from plugin and not
# from AGL binding. At 1st run ctl has invalid TLV and cannot be
# use. Bypass Solution:
# * start audio-binder before playing sound (binding create control before softvol plugin)
# * run a dummy aplay -DMyNavPCM "" to get a clean control
#
# References: https://www.spinics.net/lists/alsa-devel/msg54235.html
# --------------------------------------------------------------------
# ------------------------------------------------------
# Mixer PCM allow to play multiple stream simultaneously
# ------------------------------------------------------
pcm.Speakers {
type dmix
slave {pcm "hw:v1340"} #Jabra Solmate 1
ipc_key 1001 # ipc_key should be unique to each dmix
}
# -----------------------------------------------------
# Register ControllerHookPlugin (ToiBeFix fullpath)
# -----------------------------------------------------
pcm_hook_type.CtlHookPlugin {
install "AlsaInstallHook"
lib "/home/fulup/Workspace/Audio-4a/alsa-4a/build/hook-plugin/policy_hook_cb.so"
}
# -------------------------------------------------------
# Define one Audio Virtual Channel per Audio Roles
# -------------------------------------------------------
pcm.MusicPCM {
type softvol
# Point Slave on HOOK for policies control
slave.pcm "Speakers"
# name should match with HAL definition
control.name "Playback Multimedia"
}
pcm.NavPCM {
type softvol
# Point Slave on HOOK for policies control
slave.pcm "Speakers"
# name should match with HAL definition
control.name "Playback Navigation"
}
pcm.UrgentPCM {
type softvol
# Point Slave on HOOK for policies control
slave.pcm "Speakers"
# name should match with HAL definition
control.name "Playback Emergency"
}
# ----------------------------------------------------
# Define one hooked PCM channel per Audio Roles
# ----------------------------------------------------
pcm.Multimedia {
type hooks
slave {pcm "MusicPCM"}
hooks.0 {
comment "Defined used hook sharelib and provide arguments/config to install func"
type "CtlHookPlugin"
hook_args {
# print few log messages (default false)
verbose true
# uri to audio-4a policy engine
ws-client="unix:/var/tmp/pol4a"
# api subcall to request a role
controls {
# Request authorisation to write on navigation
navigation-ctl {
request "navigation-role"
release "release-role"
args "{'uid':'alsa-hook-navigation'}"
}
}
events { # map event reception to self generated signal
pause 30
resume 31
stop 3
}
}
}
}
```
NOTE:
* Hook plugin is loaded by Alsa libasound within client context. It inherits client process attributes, as UID/GID and
SMACK label when running on AGL. The smack label is control by AGL security framework.
As a result a control request succeeds only when client application permission match requested audio role inside Cynara security database.
* Hook plugin keep a connection with the Audio-Agent until PCM is closed by the application. This connection allow the
Audio-Agent to send events. eg: pause, quit, mute, ...
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