在前文Android—— 4.2 Vold挂载管理_VolumeManager (三) 中解析了VolumeManager是怎么样抽取Volume实例以及DirectVolume与Volume之间的关系，在上篇Android——
4.2 Vold挂载管理_NetlinkManager (四)中从kernel开始调用到handleBlockEvent，这里解析一下Vold挂载的真正操作，也就是Volume的操作！
撰写不易,转载请注明出处：http://blog.csdn.net/jscese/article/details/38736481
一.DirectVolume抽象
源码位置：/system/vold/DirectVolume.cpp ，这个类是作为真正的Volume的一个抽象操作类，先看构造：
DirectVolume::DirectVolume(VolumeManager *vm, const char *label,
const char *mount_point, int partIdx) :
Volume(vm, label, mount_point) {//同时构造父类实例
mPartIdx = partIdx;//记录分区索引
mPaths = new PathCollection();//路径容器
for (int i = 0; i < MAX_PARTITIONS; i++) //google默认最多分区数为4
mPartMinors[i] = -1;
mPendingPartMap = 0;
mDiskMajor = -1;
mDiskMinor = -1;
mDiskNumParts = 0;
setState(Volume::State_NoMedia);//初始设置状态
}
上一篇有解析到DirectVolume的handleBlockEvent：
int DirectVolume::handleBlockEvent(NetlinkEvent *evt) {
const char *dp = evt->findParam("DEVPATH"); //获取事件的设备路径
PathCollection::iterator it; //这个DirectVolume的Path容器，容器在构建时初始化，在VolumeManager中根据vold.fstab添加path
for (it = mPaths->begin(); it != mPaths->end(); ++it) {
if (!strncmp(dp, *it, strlen(*it))) { //筛选符合此次事件的Path，如果没有匹配的就退出这个DirectVolume实例的处理，在VolumeManager中交由下一个DirectVolume来处理，依次类推
/* We can handle this disk */
int action = evt->getAction();
const char *devtype = evt->findParam("DEVTYPE");
if (action == NetlinkEvent::NlActionAdd) { //事件类型有好几种，这里单以Add 添加来分析
int major = atoi(evt->findParam("MAJOR"));
int minor = atoi(evt->findParam("MINOR"));
char nodepath[255];
snprintf(nodepath,
sizeof(nodepath), "/dev/block/vold/%d:%d",
major, minor);
if (createDeviceNode(nodepath, major, minor)) { //创建节点
SLOGE("Error making device node '%s' (%s)", nodepath,
strerror(errno));
}
if (!strcmp(devtype, "disk")) {
handleDiskAdded(dp, evt); //处理型号为disk的事件，当插入一个移动设备，不管有多少个分区，首先第一个事件的类型就是disk，收集设备的相关信息，比如分区总数mDiskNumParts
} else {
handlePartitionAdded(dp, evt); //处理设备的分区事件信息
}
/* Send notification iff disk is ready (ie all partitions found) */
if (getState() == Volume::State_Idle) { //通过上面的handle ，代表已经准备就绪
char msg[255];
snprintf(msg, sizeof(msg),
"Volume %s %s disk inserted (%d:%d)", getLabel(),
getMountpoint(), mDiskMajor, mDiskMinor);
mVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeDiskInserted, //发送广播，调用的是SocketListener的sendBroadcast
msg, false);
}
}
...
}
}
}
在handlePartitionAdded中有收集分区的节点信息 mPartMinors[part_num -1] = minor; 并且设置Volume的状态到
Volume::State_Idle ，最后调用VolumeManager的实例发送广播
实际调用的是SocketListener的sendBroadcast，在Android—— 4.2 Vold挂载管理_CommandListener (二)中有分析！
void SocketListener::sendBroadcast(int code, const char *msg, bool addErrno) {
pthread_mutex_lock(&mClientsLock); //加锁
SocketClientCollection::iterator i;
for (i = mClients->begin(); i != mClients->end(); ++i) { //遍历在SocketListener时创建的Client 依次发送广播
// broadcasts are unsolicited and should not include a cmd number
if ((*i)->sendMsg(code, msg, addErrno, false)) {
SLOGW("Error sending broadcast (%s)", strerror(errno));
}
}
pthread_mutex_unlock(&mClientsLock);
}
发送过程源码位于：/system/core/libsysutils/src/SocketClient.cpp中最终调用到：
int SocketClient::sendDataLocked(const void *data, int len) {
int rc = 0;
while (brtw > 0) {
rc = send(mSocket, p, brtw, MSG_NOSIGNAL);
...
}
}
这里的mSocket 为 "vold" 这个socket的表述符！
二.Volume处理：
在上面DirectVolume中发送出去广播之后，会到上层的MountService.java中，再通过"vold"socket 到Vold中，在SocketListener 中会接收到，依次会调用到FrameworkListener.cpp中的onDataAvailable，dispatchCommand
再到CommandListener.cpp中的runCommand，VolumeManager.cpp中的mountVolume
Android—— 4.2 Vold挂载管理_CommandListener (二)中有分析！
int VolumeManager::mountVolume(const char *label) {
Volume *v = lookupVolume(label);
if (!v) {
errno = ENOENT;
return -1;
}
return v->mountVol(); //调用到Volume的mountVol
}
看Volume.cpp中：
int Volume::mountVol() {
dev_t deviceNodes[4];
int n, i, rc = 0;
char errmsg[255];
const char* externalStorage = getenv("EXTERNAL_STORAGE");
bool primaryStorage = externalStorage && !strcmp(getMountpoint(), externalStorage);
char decrypt_state[PROPERTY_VALUE_MAX];
char crypto_state[PROPERTY_VALUE_MAX];
char encrypt_progress[PROPERTY_VALUE_MAX];
int flags;
property_get("vold.decrypt", decrypt_state, "");
property_get("vold.encrypt_progress", encrypt_progress, "");
/* Don't try to mount the volumes if we have not yet entered the disk password
* or are in the process of encrypting.
*/
if ((getState() == Volume::State_NoMedia) ||
((!strcmp(decrypt_state, "1") || encrypt_progress[0]) && primaryStorage)) { //Volume的状态不对或者是加密的
snprintf(errmsg, sizeof(errmsg),
"Volume %s %s mount failed - no media",
getLabel(), getMountpoint());
mVm->getBroadcaster()->sendBroadcast(
ResponseCode::VolumeMountFailedNoMedia,
errmsg, false);
errno = ENODEV;
return -1;
} else if (getState() != Volume::State_Idle) {// 正常的逻辑到这里的时候，该Volume的state应为State_Idle
errno = EBUSY;
if (getState() == Volume::State_Pending) {
mRetryMount = true;
}
return -1;
}
...
for (i = 0; i < n; i++) {
char devicePath[255];
sprintf(devicePath, "/dev/block/vold/%d:%d", MAJOR(deviceNodes[i]),
MINOR(deviceNodes[i]));
SLOGI("%s being considered for volume %s\n", devicePath, getLabel());
errno = 0;
setState(Volume::State_Checking);
if (Fat::check(devicePath)) { //调用Fat的check，检查是否为Fat的文件系统
if (errno == ENODATA) {
SLOGW("%s does not contain a FAT filesystem\n", devicePath);
continue;
}
...
if (primaryStorage) {//是否为指定的external storage 以不同的gid挂载
// Special case the primary SD card.
// For this we grant write access to the SDCARD_RW group.
gid = AID_SDCARD_RW;
} else {
// For secondary external storage we keep things locked up.
gid = AID_MEDIA_RW;
}
if (Fat::doMount(devicePath, "/mnt/secure/staging", false, false, false, //这里就是整个Vold 里面真正的挂载
AID_SYSTEM, gid, 0702, true)) {
SLOGE("%s failed to mount via VFAT (%s)\n", devicePath, strerror(errno));
continue;
}
...
setState(Volume::State_Mounted);
...
}
}
在整个挂载流程中state至关重要，通过state对挂载流程进行管控：
Volume.h中定义：
static const int State_Init = -1;
static const int State_NoMedia = 0;
static const int State_Idle = 1;
static const int State_Pending = 2;
static const int State_Checking = 3;
static const int State_Mounted = 4;
static const int State_Unmounting = 5;
static const int State_Formatting = 6;
static const int State_Shared = 7;
static const int State_SharedMnt = 8;
同时各个state的设置都向上层发送：
void Volume::setState(int state) {
char msg[255];
int oldState = mState;
if (oldState == state) {
SLOGW("Duplicate state (%d)\n", state);
return;
}
if ((oldState == Volume::State_Pending) && (state != Volume::State_Idle)) {
mRetryMount = false;
}
mState = state;
SLOGD("Volume %s state changing %d (%s) -> %d (%s)", mLabel,
oldState, stateToStr(oldState), mState, stateToStr(mState));
snprintf(msg, sizeof(msg),
"Volume %s %s state changed from %d (%s) to %d (%s)", getLabel(),
getMountpoint(), oldState, stateToStr(oldState), mState,
stateToStr(mState));
mVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeStateChange,
msg, false);
}
简单画了一张功能流程图：
DirectVolume/Volume的大体运作就是这样，后续分析与上层Framework层的交互。