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 References: https://www.spinics.net/lists/alsa-devel/msg54235.html ## 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 - 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 - Check MultiMedia aplay -DDMyNavPCM /usr/share/sounds/alsa/test.wav ## Pulse audio integration By default Pulse only auto detect hardware sound card and virtual channel should be specified 1) update ~/.asoundrc file and check basic ALSA virtual channel works as expected 2) kill/restart pulseaudio server to force alsa hookplugin loading 3) declare alsa virtual channel as pulse sink - pacmd load-module module-alsa-sink device=MusicPCM - pacmd load-module module-alsa-sink device=NavPCM control=NavAlsaCtl - pacmd list-sinks | grep -i music 4) check your virtual pulse sink work - paplay -d alsa_output.MusicPCM /usr/share/sounds/alsa/test.wav - paplay -d alsa_output.NavPCM /usr/share/sounds/alsa/Front_Center.wav optional integration with ALSA legacy apps 5) start audio-pol4a controller - repeat previous step(3) this time with device=Multimedia device=Navigation, .... 6) check virtual channel with policy controller protection - paplay -d alsa_output.Multimedia /usr/share/sounds/alsa/test.wav - paplay -d alsa_output.Navigation /usr/share/sounds/alsa/Front_Center.wav Bug/Feature: 1) when softvol control is initialised from plugin and not from AGL binding. At 1st run ctl has invalid TLV and cannot be used Bypass Solution: * start audio-binder before playing sound (binding create control before softvol plugin) * run a dummy aplay -DMyNavPCM "" to get a clean control 2) When using Audio-Pol4a to protect virtual channel, the audio policy controller should run before adding virtual channel into pulse. 3) In order to leverage SMACK to protect virtual audio role, a Pulse rooting plugin should be used. ## Alsa Config Sample ``` # ------------------------------------------------------ # 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/alsa-hook/policy_alsa_hook.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.NaviPCM { 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 uri="unix:/var/tmp/pol4a" # timeout in ms (default 500) timeout 5000 # force API synchronous mode synchronous true # api subcall to request a role request { multimedia-role "{'uid':'alsa-hook-client'}" signal-timeout "{'timeout':180, 'music':'quit'}" } # api subcall to request a role release { release-role "{'uid':'alsa-hook-client'}" } # map AGL event on Unix signal. Search in event for json key=value events { sig-02 {search music, value quit} sig-31 {search event, value start} sig-32 {search event, value start} } } } } pcm.Navigation { type hooks slave {pcm "NaviPCM"} 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 uri="unix:/var/tmp/pol4a" # timeout in ms (default 500) timeout 5000 # force API synchronous mode synchronous true # api subcall to request a role request { navigation-role "{'uid':'alsa-hook-client'}" signal-timeout "{'timeout':5, 'navi':'quit'}" } # api subcall to request a role release { release-role "{'uid':'alsa-hook-client'}" } # map AGL event on Unix signal. Search in event for json key=value events { sig-02 {search navi, value quit} sig-31 {search event, value start} sig-32 {search event, value start} } } } } ``` 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, ...