Android(安卓)SDCard UnMounted 流程分析（二）

上一篇讲到通过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);
    }
} 复制代码

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
    } 复制代码

看一下Volume 的handleblockEvent代码：

int Volume::handleBlockEvent(NetlinkEvent *evt) {
errno = ENOSYS;
return - 1; 复制代码

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 making 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 ");
            }

             return 0;
        }
    }
    errno = ENODEV;
     return - 1;
} 复制代码

因为我的板子还未完善，所以这里它认为我的sdcard是一个分区，但无关紧要，原理一样，就根据分区的代码跟踪。:handlePartitionRemoved，由于代码过多，只贴出核心代码：

void DirectVolume::handlePartitionRemoved( const char *devpath, NetlinkEvent *evt) {

if ((dev_t) MKDEV(major, minor) == mCurrentlyMountedKdev) {
         /*
         * Yikes, our mounted partition is going away!
          */

        snprintf(msg, sizeof(msg), " Volume %s %s bad removal (%d:%d) ",
                 getLabel(), getMountpoint(), major, minor);
        SLOGD( " DirectVolume:(dev_t) MKDEV(major, minor) == mCurrentlyMountedKdev:%d,msg is :%s. ",mCurrentlyMountedKdev,msg);
         mVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeBadRemoval,
                                             msg, false);

     if (mVm->cleanupAsec( this, true)) {
            SLOGE( " Failed to cleanup ASEC - unmount will probably fail! ");
        }

         if ( Volume::unmountVol(true, false)) {
            SLOGE( " Failed to unmount volume on bad removal (%s) ",
                 strerror(errno));
             // XXX: At this point we're screwed for now
        } else {
            SLOGD( " Crisis averted ");
        }
    }
} 复制代码

到此，直接调用父类的unmountVol方法，unmountVol会通过setState通知框架状态改变。代码太多，只推荐核心代码：

int Volume::unmountVol( bool force, bool revert) {
setState(Volume::State_Unmounting);
} 复制代码

而setState会通过socket将msg消息传给框架

mVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeStateChange,
msg, false); 复制代码

接下去的步骤是关于socket的操作，就不深入了。

小结

　　　到了这一步，Vold 向上层反馈的动作基本己经完成，下一篇文章将会讲解Framework 如何取得Vold 反馈过来的数据。

小结

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