Android SDCard UnMounted 流程分析（二）

上一篇http://www.zzzyk.com/kf/201203/124631.html 讲到通过NetlinkManager发送uevent 命令到NetlinkHandler 的onEvent，代码如下：
void NetlinkHandler::onEvent(NetlinkEvent *evt) {
VolumeManager *vm = VolumeManager::Instance();
const char *subsys = evt->getSubsystem();

    if (!subsys) {
        SLOGW("No subsystem found in netlink event");
        return;
    }
    SLOGD("NetlinkHandler:OnEvent subsys values is %s",subsys);
    if (!strcmp(subsys, "block")) {
        SLOGD("NetlinkHandler:onEvent");
        vm->handleBlockEvent(evt);
    }
}

在NetlinkHandler 里面得一个VolumeManager，当收到的命令为block时调用VolumnManager的handleBlockEvent，如上加红加粗的代码。
handleBlockEvent实则是通过一个循环将事先将main事先读取的配置文件:etc/vold.fstab存进VolumeCollection，得到VolumeCollection的对象，然后调用Volume 的handleBlockEvent，如代码：
void VolumeManager::handleBlockEvent(NetlinkEvent *evt) {
    const char *devpath = evt->findParam("DEVPATH");

    /* Lookup a volume to handle this device */
    VolumeCollection::iterator it;
    bool hit = false;
    for (it = mVolumes->begin(); it != mVolumes->end(); ++it) {
        if (!(*it)->handleBlockEvent(evt)) {
#ifdef NETLINK_DEBUG
            SLOGD("Device '%s' event handled by volume %s\n", devpath, (*it)->getLabel());
#endif
            hit = true;
            break;
        }
    }

    if (!hit) {
#ifdef NETLINK_DEBUG
        SLOGW("No volumes handled block event for '%s'", devpath);
#endif
    }

看一下Volume 的handleblockEvent代码：
int Volume::handleBlockEvent(NetlinkEvent *evt) {
    errno = ENOSYS;
    return -1;

看起来好像没做什么事，其实真的实现在于Volume 的子类，DirectVolume，DirectVolme 中重写了handleBlockEvent，看代码：
int DirectVolume::handleBlockEvent(NetlinkEvent *evt) {
    const char *dp = evt->findParam("DEVPATH");

    PathCollection::iterator it;
    for (it = mPaths->begin(); it != mPaths->end(); ++it) {
        if (!strncmp(dp, *it, strlen(*it))) {
            /* We can handle this disk */
            int action = evt->getAction();
            const char *devtype = evt->findParam("DEVTYPE");

            if (action == NetlinkEvent::NlActionAdd) {
                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)) {
                    SLOGE("Error 易做图 device node '%s' (%s)", nodepath,
                                                               strerror(errno));
                }
                if (!strcmp(devtype, "disk")) {
                    handleDiskAdded(dp, evt);
                } else {
                    handlePartitionAdded(dp, evt);
                }
            } else if (action == NetlinkEvent::NlActionRemove) {
                if (!strcmp(devtype, "disk")) {
                    handleDiskRemoved(dp, evt);
                } else {
                    SLOGD("DirectVolume:handleBlockEvent--->handlePartitionRemoved");
                    handlePartitionRemoved(dp, evt);
                }
            } else if (action == NetlinkEvent::NlActionChange) {
                if (!strcmp(devtype, "disk")) {
                    handleDiskChanged(dp, evt);
                } else {
                    handlePartitionChanged(dp, evt);
                }
            } else {
                    SLOGW("Ignoring non add/remove/change event");

补充：移动开发 , Android ,