作者:gzshun. 原创作品,转载请标明出处!
来源:http://blog.csdn.net/gzshun本文分析卸载sd卡的源码,这些涉及的内容比较少,走过就行。在Android系统,系统设置里面,
提供了挂载,卸载与格式化的功能。在这里,我们可以回忆一下,Android在挂载sd卡有几个途径,
卸载又是有几种方法?
一、挂载sd卡,有2种方式:
1.用户自己挂载sd卡;
2.自动挂载sd卡,这时候是在Android系统启动完成后挂载的,所以可以看成是自动挂载;
二、卸载sd卡,有2种方式:
1.用户自己卸载sd卡;
2.用户移除sd卡;
卸载sd卡,1和2看起来有点矛盾,但这相当于平时我们在电脑使用U盘一样,
一种是先安全删除再移除U盘;
一种是不安全删除直接移除U盘;
所以在Android系统中,卸载sd卡有两个途径:
1.Framework下发卸载命令(volume unmount sdcard force),卸载sd卡;
2.vold捕获到移除事件,如果是非安全删除sd卡,那么就卸载sd卡。
所以挂载与卸载sd卡的两种方法不同,挂载sd卡都是由Framework下发命令,而卸载sd卡则不同。
一、先来分析Framework下发卸载命令:
截取CommandListener类其中的源码:
- else if (!strcmp(argv[1], "unmount")) {
- if (argc < 3 || argc > 4 || (argc == 4 && strcmp(argv[3], "force"))) {
- cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: volume unmount <path> [force]", false);
- return 0;
- }
-
- bool force = false;
- if (argc >= 4 && !strcmp(argv[3], "force")) {
- force = true;
- }
- rc = vm->unmountVolume(argv[2], force);
- }
这条卸载命令的格式是:volume unmount sdcard true/false.
这里有一个强制卸载的标志,也就是force参数,如果命令包含“force”字符串,那么就强制
卸载sd卡,接下来看unmountVolume卸载函数:
- int VolumeManager::unmountVolume(const char *label, bool force) {
- Volume *v = lookupVolume(label);
- ......
- /*这函数清理了/mnt/asec目录的一些内容,其实看不见*/
- cleanupAsec(v, force);
-
- return v->unmountVol(force);
- }
开始看卸载函数,以下函数均做简化,不再贴出大量源码,Android系统的源码实在太多:
- int Volume::unmountVol(bool force) {
- /*广播sd卡正在卸载的状态*/
- setState(Volume::State_Unmounting);
-
- if (doMoveMount(getMountpoint(), SEC_STGDIR, force)) {
- SLOGE("Failed to move mount %s => %s (%s)", getMountpoint(), SEC_STGDIR, strerror(errno));
- setState(Volume::State_Mounted);
- return -1;
- }
-
- if (doUnmount(Volume::SEC_STG_SECIMGDIR, force)) {
- SLOGE("Failed to unmount tmpfs on %s (%s)", SEC_STG_SECIMGDIR, strerror(errno));
- goto fail_republish;
- }
-
- if (doUnmount(Volume::SEC_ASECDIR, force)) {
- SLOGE("Failed to remove bindmount on %s (%s)", SEC_ASECDIR, strerror(errno));
- goto fail_remount_tmpfs;
- }
- if (doUnmount(Volume::SEC_STGDIR, force)) {
- SLOGE("Failed to unmount %s (%s)", SEC_STGDIR, strerror(errno));
- goto fail_recreate_bindmount;
- }
- /*以上doMoveMount, doUnmount等函数做些清理工作,就是之前挂载到系统的目录
- 清理干净*/
- /*卸载工作做完,告诉framework,该磁盘处于空闲状态*/
- setState(Volume::State_Idle);
- /*用来保存正在挂载的设备号的全局变量,现在赋为-1*/
- mCurrentlyMountedKdev = -1;
- return 0;
- }
二、vold捕获移除事件,调用卸载函数:
- void DirectVolume::handlePartitionRemoved(const char *devpath, NetlinkEvent *evt) {
- int major = atoi(evt->findParam("MAJOR"));
- int minor = atoi(evt->findParam("MINOR"));
- char msg[255];
- int state;
-
- SLOGD("Volume %s %s partition %d:%d removed\n", getLabel(), getMountpoint(), major, minor);
-
- /*
- * The framework doesn't need to get notified of
- * partition removal unless it's mounted. Otherwise
- * the removal notification will be sent on the Disk
- * itself
- */
- state = getState();
- if (state != Volume::State_Mounted && state != Volume::State_Shared) {
- return;
- }
- /*判断,如果移除事件的设备号与正在挂载系统的设备号相等,
- 说明此时是没有安全删除,所以下面会广播VolumeBadRemoval反馈码*/
- 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);
- mVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeBadRemoval,
- msg, false);
- /*清理asec目录*/
- if (mVm->cleanupAsec(this, true)) {
- SLOGE("Failed to cleanup ASEC - unmount will probably fail!");
- }
- /*在这里调用了卸载函数,跟framework下发命令卸载一样。*/
- if (Volume::unmountVol(true)) {
- SLOGE("Failed to unmount volume on bad removal (%s)",
- strerror(errno));
- // XXX: At this point we're screwed for now
- } else {
- SLOGD("Crisis averted");
- }
- } else if (state == Volume::State_Shared) {
- /*这里的判断是,如果此时手机与电脑正在连接着使用时,移除事件的情况*/
- /* removed during mass storage */
- snprintf(msg, sizeof(msg), "Volume %s bad removal (%d:%d)",
- getLabel(), major, minor);
- mVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeBadRemoval,
- msg, false);
- /*卸载大容量存储*/
- if (mVm->unshareVolume(getLabel(), "ums")) {
- SLOGE("Failed to unshare volume on bad removal (%s)",
- strerror(errno));
- } else {
- SLOGD("Crisis averted");
- }
- }
- }
卸载函数基本就这些,下一篇文章继续,格式化sd卡。。。
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