init.rc脚本启动vold service
service vold /system/bin/vold
class core
socket vold stream 0660 root mount
ioprio be 2
入口android/system/vold
int main() {
VolumeManager *vm;
CommandListener *cl;
NetlinkManager *nm;
SLOGI("Vold 2.1 (the revenge) firing up");
//创建vold设备文件夹
mkdir("/dev/block/vold", 0755);
/* Create our singleton managers */
//初始化Vold相关的类实例 single
if (!(vm = VolumeManager::Instance())) {
SLOGE("Unable to create VolumeManager");
exit(1);
};
if (!(nm = NetlinkManager::Instance())) {
SLOGE("Unable to create NetlinkManager");
exit(1);
};
//CommandListener 创建vold socket监听上层消息
cl = new CommandListener();
vm->setBroadcaster((SocketListener *) cl);
nm->setBroadcaster((SocketListener *) cl);
//启动VolumeManager
if (vm->start()) {
SLOGE("Unable to start VolumeManager (%s)", strerror(errno));
exit(1);
}
//根据配置文件/etc/vold.fstab 初始化VolumeManager
if (process_config(vm)) {
SLOGE("Error reading configuration (%s)... continuing anyways", strerror(errno));
}
//启动NetlinkManager socket监听内核发送uevent
if (nm->start()) {
SLOGE("Unable to start NetlinkManager (%s)", strerror(errno));
exit(1);
}
//向/sys/block/目录下所有设备uevent文件写入“add\n”,
//触发内核sysfs发送uevent消息
coldboot("/sys/block");
// coldboot("/sys/class/switch");
/*
* Now that we're up, we can respond to commands
*/
//启动CommandListener监听vold socket
if (cl->startListener()) {
SLOGE("Unable to start CommandListener (%s)", strerror(errno));
exit(1);
}
// Eventually we'll become the monitoring thread
while(1) {
sleep(1000);
}
SLOGI("Vold exiting");
exit(0);
}
Netlink通信过程分析
nm->start()
android/system/vold/NetlinkManager.cpp
int NetlinkManager::start() {
struct sockaddr_nl nladdr;
int sz = 64 * 1024;
int on = 1;
memset(&nladdr, 0, sizeof(nladdr));
nladdr.nl_family = AF_NETLINK;
nladdr.nl_pid = getpid();
nladdr.nl_groups = 0xffffffff;
//创建套接字mSock
if ((mSock = socket(PF_NETLINK,
SOCK_DGRAM,NETLINK_KOBJECT_UEVENT)) < 0) {
SLOGE("Unable to create uevent socket: %s", strerror(errno));
return -1;
}
//配置socket大小
if (setsockopt(mSock, SOL_SOCKET, SO_RCVBUFFORCE, &sz, sizeof(sz)) < 0) {
SLOGE("Unable to set uevent socket SO_RECBUFFORCE option: %s", strerror(errno));
return -1;
}
if (setsockopt(mSock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on)) < 0) {
SLOGE("Unable to set uevent socket SO_PASSCRED option: %s", strerror(errno));
return -1;
}
//bind
if (bind(mSock, (struct sockaddr *) &nladdr, sizeof(nladdr)) < 0) {
SLOGE("Unable to bind uevent socket: %s", strerror(errno));
return -1;
}
//创建NetlinkHandler传递socket,监听kernel发出的Uevent事件
mHandler = new NetlinkHandler(mSock);
if (mHandler->start()) {
SLOGE("Unable to start NetlinkHandler: %s", strerror(errno));
return -1;
}
return 0;
}
mHandler->start()
int NetlinkHandler::start() {
return this->startListener();
}
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) {
SLOGE("Obtaining file descriptor socket '%s' failed: %s",
mSocketName, strerror(errno));
return -1;
}
SLOGI("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)
mClients->push_back(new SocketClient(mSock, false, mUseCmdNum));
if (pipe(mCtrlPipe)) {
SLOGE("pipe failed (%s)", strerror(errno));
return -1;
}
if (pthread_create(&mThread, NULL, SocketListener::threadStart, this)) {
SLOGE("pthread_create (%s)", strerror(errno));
return -1;
}
return 0;
}
void *SocketListener::threadStart(void *obj) {
SocketListener *me = reinterpret_cast<SocketListener *>(obj);
me->runListener();
pthread_exit(NULL);
return NULL;
}
void SocketListener::runListener() {
SocketClientCollection *pendingList = new SocketClientCollection();
while(1) {
SocketClientCollection::iterator it;
fd_set read_fds;
int rc = 0;
int max = -1;
//1.¶Ôread_fdsÎļþÃèÊö·û¼¯Çå¿Õ
FD_ZERO(&read_fds);
//2.Ìí¼ÓÎļþÃèÊö·û
if (mListen) {
max = mSock;
//ÔÚread_fdsÎļþÃèÊö·û¼¯ÖÐÔö¼ÓmSock
FD_SET(mSock, &read_fds);
}
FD_SET(mCtrlPipe[0], &read_fds);
if (mCtrlPipe[0] > max)
max = mCtrlPipe[0];
pthread_mutex_lock(&mClientsLock);
for (it = mClients->begin(); it != mClients->end(); ++it) {
int fd = (*it)->getSocket();
FD_SET(fd, &read_fds);
if (fd > max)
max = fd;
}
pthread_mutex_unlock(&mClientsLock);
SLOGV("mListen=%d, max=%d, mSocketName=%s", mListen, max, mSocketName);
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;
//²âÊÔÖÆ¶¨µÄÎļþÃèÊö·ûÊÇ·ñÔÚ¼¯ºÏÖÐ
if (FD_ISSET(mCtrlPipe[0], &read_fds))
break;
if (mListen && FD_ISSET(mSock, &read_fds)) {
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) {
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()) {
/* 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) {
/* 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);
break;
}
}
pthread_mutex_unlock(&mClientsLock);
/* Remove our reference to the client */
c->decRef();
}
}
}
delete pendingList;
}