Android如何区分挂载的sd/usb/emmc

AOSP/system/vold/model/Dish.h
这里定义用于区分设备类型的值：

    enum Flags {
        /* Flag that disk is adoptable */
        kAdoptable = 1 << 0,
        /* Flag that disk is considered primary when the user hasn't
         * explicitly picked a primary storage location */
        kDefaultPrimary = 1 << 1,
        /* Flag that disk is SD card */
        kSd = 1 << 2,
        /* Flag that disk is USB disk */
        kUsb = 1 << 3,
        /* Flag that disk is EMMC internal */
        kEmmc = 1 << 4,
    };

这个值会在挂载的时候用到：

void VolumeManager::handleBlockEvent(NetlinkEvent *evt) {
    std::lock_guard<std::mutex> lock(mLock);

    if (mDebug) {
        LOG(VERBOSE) << "----------------";
        LOG(VERBOSE) << "handleBlockEvent with action " << (int) evt->getAction();
        evt->dump();
    }

    std::string eventPath(evt->findParam("DEVPATH")?evt->findParam("DEVPATH"):"");
    std::string devType(evt->findParam("DEVTYPE")?evt->findParam("DEVTYPE"):"");

    if (devType != "disk") return;

    int major = std::stoi(evt->findParam("MAJOR"));
    int minor = std::stoi(evt->findParam("MINOR"));
    dev_t device = makedev(major, minor);

    switch (evt->getAction()) {
    case NetlinkEvent::Action::kAdd: {
        for (const auto& source : mDiskSources) {
            if (source->matches(eventPath)) {
                // For now, assume that MMC and virtio-blk (the latter is
                // emulator-specific; see Disk.cpp for details) devices are SD,
                // and that everything else is USB
                int flags = source->getFlags();
                if (major == kMajorBlockMmc
                    || (android::vold::IsRunningInEmulator()
                    && major >= (int) kMajorBlockExperimentalMin
                    && major <= (int) kMajorBlockExperimentalMax)) {
                    flags |= android::vold::Disk::Flags::kSd;
                } else {
                    flags |= android::vold::Disk::Flags::kUsb;
                }

最终，挂载的设备被封装成VolumeInfo，传到StorageManagerService：

    private void onVolumeCreatedLocked(VolumeInfo vol) {
        ...
        if (vol.disk.isAdoptable()) {
                vol.mountFlags |= VolumeInfo.MOUNT_FLAG_VISIBLE;
        }

我们可以通过vol.disk.isUsb()等方法来判断设备类型。

让sd卡被识别为usb

修改Dish.h即可：

        /* Flag that disk is SD card */
        // 让sd卡当成usb
        kSd = 1 << 3,
        /* Flag that disk is USB disk */
        kUsb = 1 << 3,