在android usb挂载分析----vold启动&＃xff0c;我们的vold模块已经启动了&＃xff0c;通信的机制也已经建立起来了&＃xff0c;接下来我们分析一下MountService的启动&＃xff0c;也就是我们FrameWork层的启动&＃xff0c;首先看下其大概流程&＃xff1a;
MountService的启动在SystemServer.java中&＃xff0c;有如下代码&＃xff1a;
[cpp] view plain copy print ?
try{
/*
* NotificationManagerService is dependant on MountService,
* (for media / usb notifications) so we must start MountService first.
*/
Slog.i(TAG, "Mount Service");
ServiceManager.addService("mount",newMountService(context));
} catch(Throwable e) {
Slog.e(TAG, "Failure starting Mount Service", e);
} 这里new 了一个
MountService&＃xff0c;并把service添加到了
ServiceManager,我们看下MountService的构造函数&＃xff1a;
[cpp] view plain copy print ?
/**
* Constructs a new MountService instance
*
* &＃64;param context Binder context for this service
*/
publicMountService(Context context) {
mContext &＃61; context;
// XXX: This will go away soon in favor of IMountServiceObserver
mPms &＃61; (PackageManagerService) ServiceManager.getService("package");//获取包管理服务
mContext.registerReceiver(mBroadcastReceiver,
newIntentFilter(Intent.ACTION_BOOT_COMPLETED), null, null);//注册广播接收器
mHandlerThread &＃61; newHandlerThread("MountService");//处理消息
mHandlerThread.start();
mHandler &＃61; newMountServiceHandler(mHandlerThread.getLooper());
// Add OBB Action Handler to MountService thread.
mObbActionHandler &＃61; newObbActionHandler(mHandlerThread.getLooper());
/*
* Vold does not run in the simulator, so pretend the connector thread
* ran and did its thing.
*/
if("simulator".equals(SystemProperties.get("ro.product.device"))) {
mReady &＃61; true;
mUmsEnabling &＃61; true;
return;
}
/*
* Create the connection to vold with a maximum queue of twice the
* amount of containers we&＃39;d ever expect to have. This keeps an
* "asec list" from blocking a thread repeatedly.
*/
mConnector &＃61; newNativeDaemonConnector(this,"vold",
PackageManagerService.MAX_CONTAINERS * 2, VOLD_TAG);
mReady &＃61; false;
Thread thread&＃61;newThread(mConnector, VOLD_TAG);
thread.start();
} 后面new 了一个NativeDaemonConnector&＃xff0c;注意这里传递了一个"vold"字符串&＃xff0c;跟我们在vold启动的时候传给CommandListener是一样的。
接下来调用 thread.start()启动线程&＃xff0c;我们看下它的run函数
[cpp] view plain copy print ?
publicvoidrun() {
while(true) {
try{
listenToSocket();
} catch(Exception e) {
Slog.e(TAG, "Error in NativeDaemonConnector", e);
SystemClock.sleep(5000);
}
}
} 在循环中调用listenToSocket函数&＃xff0c;看下这个函数
[cpp] view plain copy print ?
privatevoidlistenToSocket() throws IOException {
LocalSocket socket &＃61; null;
try{
socket &＃61; newLocalSocket();
LocalSocketAddress address &＃61; newLocalSocketAddress(mSocket,//这里mSocket&＃61;“vold"
LocalSocketAddress.Namespace.RESERVED); //注意这里的RESERVED
socket.connect(address); //连接到vold模块监听的套接字处
mCallbacks.onDaemonConnected(); //实现在MountService中
InputStream inputStream &＃61; socket.getInputStream();
mOutputStream &＃61; socket.getOutputStream();
byte[] buffer &＃61; newbyte[BUFFER_SIZE];
intstart &＃61; 0;
while(true) {
intcount &＃61; inputStream.read(buffer, start, BUFFER_SIZE - start);//读取消息
if(count break;
// Add our starting point to the count and reset the start.
count &＃43;&＃61; start;
start &＃61; 0;
for(inti &＃61; 0; i
if(buffer[i] &＃61;&＃61; 0) {
String event &＃61; newString(buffer, start, i - start);
if(LOCAL_LOGD) Slog.d(TAG, String.format("RCV , event));
String[] tokens &＃61; event.split(" ");
try{
intcode &＃61; Integer.parseInt(tokens[0]);
if(code >&＃61; ResponseCode.UnsolicitedInformational) {
try{
if(!mCallbacks.onEvent(code, event, tokens)) {//实现在MountService中
Slog.w(TAG, String.format(
"Unhandled event (%s)", event));
}
} catch(Exception ex) {
Slog.e(TAG, String.format(
"Error handling &＃39;%s&＃39;", event), ex);
}
}
try{
mResponseQueue.put(event);
} catch(InterruptedException ex) {
Slog.e(TAG, "Failed to put response onto queue", ex);
}
} catch(NumberFormatException nfe) {
Slog.w(TAG, String.format("Bad msg (%s)", event));
}
start &＃61; i &＃43; 1;
}
}
// We should end at the amount we read. If not, compact then
// buffer and read again.
if(start !&＃61; count) {
final intremaining &＃61; BUFFER_SIZE - start;
System.arraycopy(buffer, start, buffer, 0, remaining);
start &＃61; remaining;
} else{
start &＃61; 0;
}
}
} catch(IOException ex) {
Slog.e(TAG, "Communications error", ex);
throwex;
} finally {
synchronized (this) {
if(mOutputStream !&＃61; null) {
try{
mOutputStream.close();
} catch(IOException e) {
Slog.w(TAG, "Failed closing output stream", e);
}
mOutputStream &＃61; null;
}
}
try{
if(socket !&＃61; null) {
socket.close();
}
} catch(IOException ex) {
Slog.w(TAG, "Failed closing socket", ex);
}
}
}
onDaemonConnected的实现在MountServices吕&＃xff0c;将向下下发volume list消息 获取到了磁盘的标签&＃xff0c;挂载点与状态&＃xff0c;调用connect函数连接到vold模块&＃xff0c;connetc最终调用native函数connectLocal进行连接工作&＃xff0c;我们看下他的jni层代码&＃xff0c;最后调用的&＃xff1a;
[cpp] view plain copy print ?
intsocket_local_client_connect(intfd,constchar*name,intnamespaceId,
inttype)
{
structsockaddr_un addr;
socklen_t alen;
size_tnamelen;
interr;
err &＃61; socket_make_sockaddr_un(name, namespaceId, &addr, &alen);
if(err
gotoerror;
}
if(connect(fd, (structsockaddr *) &addr, alen)
gotoerror;
}
returnfd;
error:
return-1;
}
/**
* connect to peer named "name"
* returns fd or -1 on error
*/
我们再跟进socket_make_sockaddr_un函数&＃xff0c;这时namespaceId传的ANDROID_SOCKET_NAMESPACE_RESERVED,所以会执行下面几句&＃xff1a;
[cpp] view plain copy print ?
caseANDROID_SOCKET_NAMESPACE_RESERVED:
namelen &＃61; strlen(name) &＃43; strlen(ANDROID_RESERVED_SOCKET_PREFIX);
/* unix_path_max appears to be missing on linux */
if(namelen >sizeof(*p_addr)
- offsetof(structsockaddr_un, sun_path) - 1) {
gotoerror;
}
strcpy(p_addr->sun_path, ANDROID_RESERVED_SOCKET_PREFIX); // ANDROID_RESERVED_SOCKET_PREFIX&＃61;"/dev/socket/"
strcat(p_addr->sun_path, name);
break;
注意在前面 connect 函数中的套接字的构造&＃xff0c;使用了AF_LOCAL&＃xff1a;
[cpp] view plain copy print ?
intsocket_local_client(constchar*name,intnamespaceId,inttype)
{
ints;
s &＃61; socket("color:#ff0000;">AF_LOCAL, type, 0);
if(s return-1;
if( 0 > socket_local_client_connect(s, name, namespaceId, type)) {
close(s);
return-1;
}
returns;
} 这样&＃xff0c;就建立了一条从FrameWork层到vold层的通信链路&＃xff0c;后面FrameWork层就等待Vold发送消息过来了。。。FrameWork层的通信也ok了&＃xff0c;就可以等待U盘挂载了。。
转自&＃xff1a;http://blog.csdn.net/new_abc/article/details/7400740
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