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Android—— 4.2 Vold挂载管理_CommandListener (二)
在前一篇博客中介绍了个大体结构 Android—— 4.2 Vold挂载管理_主体构建 (一) ,按照代码的顺序结构来依次分析,这里来看看CommandListener这个类做了什么。
撰写不易,转载请注明出处:http://blog.csdn.net/jscese/article/details/38434263
一:CommandListener构造
在/system/vold/main.cpp的main函数中构建实例:
cl = new CommandListener(); vm->setBroadcaster((SocketListener *) cl); nm->setBroadcaster((SocketListener *) cl); ... /* * Now that we're up, we can respond to commands */ if (cl->startListener()) { SLOGE("Unable to start CommandListener (%s)", strerror(errno)); exit(1); }
源码位于/system/vold/CommandListener.cpp,构造函数如下:
CommandListener::CommandListener() : FrameworkListener("vold", true) { registerCmd(new DumpCmd()); registerCmd(new VolumeCmd()); registerCmd(new AsecCmd()); registerCmd(new ObbCmd()); registerCmd(new StorageCmd()); registerCmd(new XwarpCmd()); registerCmd(new CryptfsCmd()); }
构造一个父类FrameworkListener的实例
先看FrameworkListener的构造:
FrameworkListener::FrameworkListener(const char *socketName, bool withSeq) : SocketListener(socketName, true, withSeq) { init(socketName, withSeq); } .. void FrameworkListener::init(const char *socketName, bool withSeq) { mCommands = new FrameworkCommandCollection(); errorRate = 0; mCommandCount = 0; mWithSeq = withSeq; }
可以看到传进去的"vold" 没在这个类里面起作用,是为了更高一层的构造,接着看/system/core/libsysutils/src/SocketListener.cpp中:
SocketListener::SocketListener(const char *socketName, bool listen, bool useCmdNum) { init(socketName, -1, listen, useCmdNum); } void SocketListener::init(const char *socketName, int socketFd, bool listen, bool useCmdNum) { mListen = listen; mSocketName = socketName; mSock = socketFd; mUseCmdNum = useCmdNum; pthread_mutex_init(&mClientsLock, NULL); mClients = new SocketClientCollection(); }初始化线程锁mClientsLock,new 了一个SocketClient的容器mClients。
继承关系: CommandListener——>FrameworkListener——>SocketListener
二:Command注册
上面的CommandListener的构造函数中调用父类的注册函数register, 注册commad到FrameworkListener的mCommands容器中。
/system/core/libsysutils/src/FrameworkListener.cpp注册如下:
void FrameworkListener::registerCmd(FrameworkCommand *cmd) { mCommands->push_back(cmd); }
可以看到这里的行参是FrameworkCommand 类型,
因为这几个command类的继承关系: VolumeCmd——>VoldCommand——>FrameworkCommand
我们这里以VolumeCmd 为例子学习:
CommandListener::VolumeCmd::VolumeCmd() : VoldCommand("volume") { }
VoldCommand::VoldCommand(const char *cmd) : FrameworkCommand(cmd) { }
FrameworkCommand::FrameworkCommand(const char *cmd) { mCommand = cmd; }
将volume这个command注册到mCommands这个容器中之后,目的是当FrameworkListerer从SlocketListener接收到command的时候,
会依据mCommands 中的command进行解析筛选判断分发,调用对应的command执行类。
三:CommandListener运作
CommandListener所起到的作用,简单来说就是沟通Framwork和Vold,我画的一张简单的结构图,大体的运作如下:
开启CommandListener的监听cl->startListener()
CommandListener和FrameworkListener都没有重写这个方法,直接调用父类SocketListener的:
int SocketListener::startListener() { if (!mSocketName && mSock == -1) { SLOGE("Failed to start unbound listener"); errno = EINVAL; return -1; } else if (mSocketName) { if ((mSock = android_get_control_socket(mSocketName)) < 0) {//获取socket的文件描述符,这里是获取Vold这个socket的 SLOGE("Obtaining file descriptor socket '%s' failed: %s", mSocketName, strerror(errno)); return -1; } SLOGV("got mSock = %d for %s", mSock, mSocketName); } if (mListen && listen(mSock, 4) < 0) { SLOGE("Unable to listen on socket (%s)", strerror(errno)); return -1; } else if (!mListen)//是否正常监听socket mClients->push_back(new SocketClient(mSock, false, mUseCmdNum)); if (pipe(mCtrlPipe)) {//新建管道,保存文件描述符到数组 SLOGE("pipe failed (%s)", strerror(errno)); return -1; } if (pthread_create(&mThread, NULL, SocketListener::threadStart, this)) {//开了一个线程来处理 SLOGE("pthread_create (%s)", strerror(errno)); return -1; } return 0; }
往下新开了一个线程用于监听:
void *SocketListener::threadStart(void *obj) { SocketListener *me = reinterpret_cast<SocketListener *>(obj);//threadStart为static函数,上面开线程创建的时候传了this,这里需要转换一个一样bit位的SocketListener指针 me->runListener();//SocketListener真正的执行函数 pthread_exit(NULL); return NULL; }
下面就是对Socket的监听处理:
void SocketListener::runListener() { SocketClientCollection *pendingList = new SocketClientCollection();//暂存mClients中的SocketClient while(1) { SocketClientCollection::iterator it; fd_set read_fds; int rc = 0; int max = -1; FD_ZERO(&read_fds);//清空文件描述符集read_fds if (mListen) { max = mSock; FD_SET(mSock, &read_fds);//如果正常的监听,这里就把之前获得的vold的文件描述符添加进去 } FD_SET(mCtrlPipe[0], &read_fds);//添加管道读取端的文件描述符 if (mCtrlPipe[0] > max) max = mCtrlPipe[0]; pthread_mutex_lock(&mClientsLock);//加锁操作,多线程安全 for (it = mClients->begin(); it != mClients->end(); ++it) {//遍历mClients,获取fd 添加到read_fds int fd = (*it)->getSocket(); FD_SET(fd, &read_fds); if (fd > max) max = fd; } pthread_mutex_unlock(&mClientsLock);//解锁 SLOGV("mListen=%d, max=%d, mSocketName=%s", mListen, max, mSocketName); //linux下socket编程的select,这里检测read_fds集合里面是否有可读的,也就是有没有数据过来,没有数据的文件描述符会从read_fds中被剔除,这里的select设置time out为NULL,阻塞操作,直到read_fds集合中描述符有变化 if ((rc = select(max + 1, &read_fds, NULL, NULL, NULL)) < 0) { if (errno == EINTR) continue; SLOGE("select failed (%s) mListen=%d, max=%d", strerror(errno), mListen, max); sleep(1); continue; } else if (!rc) continue; if (FD_ISSET(mCtrlPipe[0], &read_fds))//如果匿名管道有数据可读,就退出 break; if (mListen && FD_ISSET(mSock, &read_fds)) {//如果是正常监听的 mListen 为true,然后mSock这个描述符有可读数据,就创建链接,新建异步处理的SocketClient加入到mClients容器,这里的mSock 是vold这个套接字的描述符 struct sockaddr addr; socklen_t alen; int c; do { alen = sizeof(addr); c = accept(mSock, &addr, &alen); SLOGV("%s got %d from accept", mSocketName, c); } while (c < 0 && errno == EINTR); if (c < 0) { SLOGE("accept failed (%s)", strerror(errno)); sleep(1); continue; } pthread_mutex_lock(&mClientsLock); mClients->push_back(new SocketClient(c, true, mUseCmdNum)); pthread_mutex_unlock(&mClientsLock); } /* Add all active clients to the pending list first */ pendingList->clear(); pthread_mutex_lock(&mClientsLock); for (it = mClients->begin(); it != mClients->end(); ++it) {//把上面有请求建立链接的Client加入到pendingList 容器中,后面处理 int fd = (*it)->getSocket(); if (FD_ISSET(fd, &read_fds)) { pendingList->push_back(*it); } } pthread_mutex_unlock(&mClientsLock); /* Process the pending list, since it is owned by the thread, * there is no need to lock it */ while (!pendingList->empty()) {//遍历处理 /* Pop the first item from the list */ it = pendingList->begin(); SocketClient* c = *it; pendingList->erase(it); /* Process it, if false is returned and our sockets are * connection-based, remove and destroy it */ if (!onDataAvailable(c) && mListen) {//调用到FrameworkListener 中onDataAvailable处理Socket事件 /* Remove the client from our array */ SLOGV("going to zap %d for %s", c->getSocket(), mSocketName); pthread_mutex_lock(&mClientsLock); for (it = mClients->begin(); it != mClients->end(); ++it) { if (*it == c) { mClients->erase(it);//处理完成之后,从容器中移除这次的监听到的SocketClient break; } } pthread_mutex_unlock(&mClientsLock); /* Remove our reference to the client */ c->decRef(); } } } delete pendingList; }
这个函数是SocketListener的核心所在,真正的处理函数是onDataAvailable,这个是纯虚函数,/system/core/include/sysutils/SocketListener.h:
virtual bool onDataAvailable(SocketClient *c) = 0;
在其子类 FrameworkListener.cpp中实现:
bool FrameworkListener::onDataAvailable(SocketClient *c) { char buffer[255]; int len; len = TEMP_FAILURE_RETRY(read(c->getSocket(), buffer, sizeof(buffer)));//读Socket 内容保存到buffer if (len < 0) { SLOGE("read() failed (%s)", strerror(errno)); return false; } else if (!len) return false; int offset = 0; int i; for (i = 0; i < len; i++) { if (buffer[i] == '\0') {//一次传入一个字符串 /* IMPORTANT: dispatchCommand() expects a zero-terminated string */ dispatchCommand(c, buffer + offset); offset = i + 1; } } return true; }
调用同类命令执行函数dispatchCommand:
void FrameworkListener::dispatchCommand(SocketClient *cli, char *data) { FrameworkCommandCollection::iterator i; int argc = 0; char *argv[FrameworkListener::CMD_ARGS_MAX]; char tmp[255]; ...//解析判断command buffer for (i = mCommands->begin(); i != mCommands->end(); ++i) {//遍历之前register到FrameworkListener中的FrameworkCommand容器 FrameworkCommand *c = *i; if (!strcmp(argv[0], c->getCommand())) {//其中有注册“Volume”,如果这里是Volume开头的command,那么就调用,Volume构造的时候所构造的父类FrameworkCommand中的runCommand函数 if (c->runCommand(cli, argc, argv)) { SLOGW("Handler '%s' error (%s)", c->getCommand(), strerror(errno)); } goto out; } } }
同时/system/core/include/sysutils/FrameworkCommand.h:
virtual int runCommand(SocketClient *c, int argc, char **argv) = 0;
实现在子类中,还是以Volume这个runcommand为例 /system/vold/CommandListener.cpp中:
int CommandListener::VolumeCmd::runCommand(SocketClient *cli, int argc, char **argv) { dumpArgs(argc, argv, -1); if (argc < 2) { cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing Argument", false); return 0; } VolumeManager *vm = VolumeManager::Instance();//获取已经存在的VolumeManager实例 ... else if (!strcmp(argv[1], "mount")) {//判断command 内容 if (argc != 3) { cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: volume mount <path>", false); return 0; } rc = vm->mountVolume(argv[2]);//交给VolumeManager来对Volume进行操作 } ... }
对CommandListener的分析就到这里,主要是怎么接收到的Socket,执行相对应的command,最后是怎么传递给VolumeManager,与上层MountService的交互后续分析,后续分析VolumeManager的初始化!