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Alsa-Hook-Plugin
Object: Provide a Hook on Alsa PCM to check permission again AGL Advance Audio Agent
Status: Working Proof of Concept
Author: Fulup Ar Foll fulup@iot.bzh
Date : August-2017
Functionalities:
- Execute a set of websocket RPC request again AGL binders to allow/deny access
- Keep websocket open in an idepandant thread on order to monitor event receive 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)
Config
```
# Define sharelib location and entry point
# -----------------------------------------
pcm_hook_type.MyHookPlugin {
install "AlsaInstallHook"
lib "/home/fulup/Workspace/AGL-AppFW/audio-bindings-dev/build/Alsa-Plugin/Alsa-Hook-Callback/alsa_hook_cb.so"
}
# Create PCM HOOK with corresponding request calls to AGL Audio Agent
# --------------------------------------------------------------------
pcm.MyNavigationHook {
type hooks
slave.pcm "MyMixerPCM" # Target PCM to effectively play sound
# Call request that should succeed before accessing slave PCM
hooks.0 {
type "MyHookPlugin" # Name=xxxx should match with pcm_hook_type.xxxx
hook_args {
# URI to AGL-Advance-Audio-Agent binder
uri "ws://localhost:1234/api?token='audio-agent-token'"
# Call request to send to binder (initial label is free, query is optional)
request {
MyFirstCheck {
api "alsacore"
verb "ping"
}
MySecondCheck {
api "alsacore"
verb "ucmset"
query "{'devid':'hw:v1340','verb':'Navigation','dev':'speakers'}"
}
}
}
}
}
```
NOTE:
* Hook plugin is loaded by Alsa libasound within player context. It inherits client process attributes, as UID/GID or
the SMACK label on AGL. This smack label is tested by AGL security framework when requested a call on the audio-agent binder.
As a result the call will only succeed it the permission attached the application in Cynara matches.
* 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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