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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"
# Defined used hook sharelib and provide arguments/config to install func
hooks.0 {
type "MyHookPlugin"
hook_args {
verbose true # print few log messages (default false);
# Every Call should return OK in order PCM to open (default timeout 100ms)
uri "ws://localhost:1234/api?token='audio-agent-token'"
request {
# Request autorisation to write on navigation
RequestNavigation {
api "polctl"
verb "navigation"
}
# subscribe to Audio Agent Event
SubscriveEvents {
api "polctl"
verb "monitor"
}
# force PCM stop after 10s
TestAutoStop {
api "polctl"
verb "event_test"
query "{'label':'stop', 'delay':10000}"
}
}
}
}
}
```
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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