Move to support Audio-4a High Level API

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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
+ 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, ...
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