Android6.0 otg插入U盘 流程
之前分析过vold插入sd卡的流程，本以为otg插入U盘与sd卡走的流程一样。想不到还是有差别的，下面我们来分析下：
一、kAdoptable flag
先来看otg插入卡，后handleBlockEvent的流程
void VolumeManager::handleBlockEvent(NetlinkEvent *evt) {
std::lock_guard<std::mutex> lock(mLock);
std::string eventPath(evt->findParam("DEVPATH"));
std::string devType(evt->findParam("DEVTYPE"));
if (devType != "disk") return;
int major = atoi(evt->findParam("MAJOR"));
int minor = atoi(evt->findParam("MINOR"));
dev_t device = makedev(major, minor);
switch (evt->getAction()) {
case NetlinkEvent::Action::kAdd: {
for (auto source : mDiskSources) {
if (source->matches(eventPath)) {
// For now, assume that MMC devices are SD, and that
// everything else is USB
int flags = source->getFlags();
if (flags & android::vold::Disk::Flags::kAdoptable) {//这边的log是自己调试的时候加的
PLOG(ERROR) << "add disk kAdoptable";
}
if (major == kMajorBlockMmc) {
flags |= android::vold::Disk::Flags::kSd;//加入sd的flag
} else {
LOG(DEBUG) << "usb disk add.";
flags |= android::vold::Disk::Flags::kUsb;//加入usb的flag
}
auto disk = new android::vold::Disk(eventPath, device,
source->getNickname(), flags);
disk->create();
mDisks.push_back(std::shared_ptr<android::vold::Disk>(disk));
break;
}
}
break;
}
......
}
上面的函数我们自己加了log，当走sd卡的时候从底层传上来的flag中就有kAdoptable，而如果是usb的就没有kAdoptable这个flag。
这点差别也会导致上层MountService处理的差别。
二、MountFlags MOUNT_FLAG_VISIBLE
private void onVolumeCreatedLocked(VolumeInfo vol) {
if (vol.type == VolumeInfo.TYPE_EMULATED) {
final StorageManager storage = mContext.getSystemService(StorageManager.class);
final VolumeInfo privateVol = storage.findPrivateForEmulated(vol);
if (Objects.equals(StorageManager.UUID_PRIVATE_INTERNAL, mPrimaryStorageUuid)
&& VolumeInfo.ID_PRIVATE_INTERNAL.equals(privateVol.id)) {
Slog.v(TAG, "Found primary storage at " + vol);
vol.mountFlags |= VolumeInfo.MOUNT_FLAG_PRIMARY;
vol.mountFlags |= VolumeInfo.MOUNT_FLAG_VISIBLE;
mHandler.obtainMessage(H_VOLUME_MOUNT, vol).sendToTarget();
} else if (Objects.equals(privateVol.fsUuid, mPrimaryStorageUuid)) {
Slog.v(TAG, "Found primary storage at " + vol);
vol.mountFlags |= VolumeInfo.MOUNT_FLAG_PRIMARY;
vol.mountFlags |= VolumeInfo.MOUNT_FLAG_VISIBLE;
mHandler.obtainMessage(H_VOLUME_MOUNT, vol).sendToTarget();
}
} else if (vol.type == VolumeInfo.TYPE_PUBLIC) {//sd卡和otg都是Public
Slog.d(TAG, "kangchen VolumeInfo.TYPE_PUBLIC");
// TODO: only look at first public partition
if (Objects.equals(StorageManager.UUID_PRIMARY_PHYSICAL, mPrimaryStorageUuid)
&& vol.disk.isDefaultPrimary()) {
Slog.d(TAG, "kangchen UUID_PRIMARY_PHYSICAL");
Slog.v(TAG, "Found primary storage at " + vol);
vol.mountFlags |= VolumeInfo.MOUNT_FLAG_PRIMARY;
vol.mountFlags |= VolumeInfo.MOUNT_FLAG_VISIBLE;
}
// Adoptable public disks are visible to apps, since they meet
// public API requirement of being in a stable location.
if (vol.disk.isAdoptable()) {//如果有kAdoptable这个flag
vol.mountFlags |= VolumeInfo.MOUNT_FLAG_VISIBLE;
}
vol.mountUserId = UserHandle.USER_OWNER;
mHandler.obtainMessage(H_VOLUME_MOUNT, vol).sendToTarget();
} else if (vol.type == VolumeInfo.TYPE_PRIVATE) {
mHandler.obtainMessage(H_VOLUME_MOUNT, vol).sendToTarget();
} else {
Slog.d(TAG, "Skipping automatic mounting of " + vol);
}
}
从上面处理volume创建来看，如果Disk有kAdoptable这个flag，那么往vold传的mountFlags |= VolumeInfo.MOUNT_FLAG_VISIBLE
三、vold otg的挂载流程
下面我们再来看vold中PublicVolume的挂载：
status_t PublicVolume::doMount() {
// TODO: expand to support mounting other filesystems
readMetadata();
if (mFsType != "vfat") {
LOG(ERROR) << getId() << " unsupported filesystem " << mFsType;
return -EIO;
}
if (vfat::Check(mDevPath)) {
LOG(ERROR) << getId() << " failed filesystem check";
return -EIO;
}
// Use UUID as stable name, if available
std::string stableName = getId();
if (!mFsUuid.empty()) {
stableName = mFsUuid;
}
mRawPath = StringPrintf("/mnt/media_rw/%s", stableName.c_str());
mFuseDefault = StringPrintf("/mnt/runtime/default/%s", stableName.c_str());
mFuseRead = StringPrintf("/mnt/runtime/read/%s", stableName.c_str());
mFuseWrite = StringPrintf("/mnt/runtime/write/%s", stableName.c_str());
setInternalPath(mRawPath);
if (getMountFlags() & MountFlags::kVisible) {
setPath(StringPrintf("/storage/%s", stableName.c_str()));
} else {
setPath(mRawPath);
}
//创建挂载目录，以及各个fuse目录
if (fs_prepare_dir(mRawPath.c_str(), 0700, AID_ROOT, AID_ROOT) ||
fs_prepare_dir(mFuseDefault.c_str(), 0700, AID_ROOT, AID_ROOT) ||
fs_prepare_dir(mFuseRead.c_str(), 0700, AID_ROOT, AID_ROOT) ||
fs_prepare_dir(mFuseWrite.c_str(), 0700, AID_ROOT, AID_ROOT)) {
PLOG(ERROR) << getId() << " failed to create mount points";
return -errno;
}
if (vfat::Mount(mDevPath, mRawPath, false, false, false,
AID_MEDIA_RW, AID_MEDIA_RW, 0007, true)) {
PLOG(ERROR) << getId() << " failed to mount " << mDevPath;
return -EIO;
}
if (getMountFlags() & MountFlags::kPrimary) {
initAsecStage();
}
if (!(getMountFlags() & MountFlags::kVisible)) {//如果MountService没有传kVisible这个flag下来，那么就不进行fuse操作了。
// Not visible to apps, so no need to spin up FUSE
return OK;
}
dev_t before = GetDevice(mFuseWrite);
if (!(mFusePid = fork())) {
if (getMountFlags() & MountFlags::kPrimary) {
if (execl(kFusePath, kFusePath,
"-u", "1023", // AID_MEDIA_RW
"-g", "1023", // AID_MEDIA_RW
"-U", std::to_string(getMountUserId()).c_str(),
"-w",
mRawPath.c_str(),
stableName.c_str(),
NULL)) {
PLOG(ERROR) << "Failed to exec";
}
} else {
if (execl(kFusePath, kFusePath,
"-u", "1023", // AID_MEDIA_RW
"-g", "1023", // AID_MEDIA_RW
"-U", std::to_string(getMountUserId()).c_str(),
mRawPath.c_str(),
stableName.c_str(),
NULL)) {
PLOG(ERROR) << "Failed to exec";
}
}
LOG(ERROR) << "FUSE exiting";
_exit(1);
}
if (mFusePid == -1) {
PLOG(ERROR) << getId() << " failed to fork";
return -errno;
}
while (before == GetDevice(mFuseWrite)) {
LOG(VERBOSE) << "Waiting for FUSE to spin up...";
usleep(50000); // 50ms
}
return OK;
}
而我们看PublicVolume的挂载流程，当MountService传的MountFlag没有kVisible这个flag的话，就直接挂载完就结束了，不会再走fuse流程了。
所以在storage下面是看不到otg的U盘路径的，这里说错了，因为前面fuse的路径是创建了，但是没有fuse上，所以storage下的这个路径是无效的。
所以上面的代码需要修改下：
status_t PublicVolume::doMount() {
// TODO: expand to support mounting other filesystems
readMetadata();
if (mFsType != "vfat") {
LOG(ERROR) << getId() << " unsupported filesystem " << mFsType;
return -EIO;
}
if (vfat::Check(mDevPath)) {
LOG(ERROR) << getId() << " failed filesystem check";
return -EIO;
}
// Use UUID as stable name, if available
std::string stableName = getId();
if (!mFsUuid.empty()) {
stableName = mFsUuid;
}
mRawPath = StringPrintf("/mnt/media_rw/%s", stableName.c_str());
mFuseDefault = StringPrintf("/mnt/runtime/default/%s", stableName.c_str());
mFuseRead = StringPrintf("/mnt/runtime/read/%s", stableName.c_str());
mFuseWrite = StringPrintf("/mnt/runtime/write/%s", stableName.c_str());
setInternalPath(mRawPath);
if (getMountFlags() & MountFlags::kVisible) {
setPath(StringPrintf("/storage/%s", stableName.c_str()));
} else {
setPath(mRawPath);
}
if (fs_prepare_dir(mRawPath.c_str(), 0700, AID_ROOT, AID_ROOT)) {
PLOG(ERROR) << getId() << " failed to create mount points";
return -errno;
}
if (vfat::Mount(mDevPath, mRawPath, false, false, false,
AID_MEDIA_RW, AID_MEDIA_RW, 0007, true)) {
PLOG(ERROR) << getId() << " failed to mount " << mDevPath;
return -EIO;
}
if (getMountFlags() & MountFlags::kPrimary) {
initAsecStage();
}
if (!(getMountFlags() & MountFlags::kVisible)) {
// Not visible to apps, so no need to spin up FUSE
return OK;
}
if (fs_prepare_dir(mFuseDefault.c_str(), 0700, AID_ROOT, AID_ROOT) ||
fs_prepare_dir(mFuseRead.c_str(), 0700, AID_ROOT, AID_ROOT) ||
fs_prepare_dir(mFuseWrite.c_str(), 0700, AID_ROOT, AID_ROOT)) {
PLOG(ERROR) << getId() << " failed to create fuse points";
return -errno;
}
//执行fuse操作
.......
return OK;
}
上面如果是otg的话，创建的fuse路径也就没有什么用，所以我们把mount的路径放前面，fuse的路径放后面，这样挂载otg后也就不会有fuse这个没有用的路径生成了。
所以这样的话otg挂载的volume，拿到路径的话，也是没有权限的。因为挂载的路径是mnt/media下面的需要的权限需要：
<permission name="android.permission.WRITE_MEDIA_STORAGE" >
<group gid="media_rw" />
<group gid="sdcard_rw" />
</permission>