詳談android 6.0 fuse文件系統(tǒng)的掛載和卸載問題
更新時(shí)間：2018年08月02日 09:39:56 作者：kc專欄
今天小編就為大家分享一篇詳談android 6.0 fuse文件系統(tǒng)的掛載和卸載問題，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。一起跟隨小編過來看看吧
android4.4 的時(shí)候vold，也是利用fuse文件系統(tǒng)達(dá)到，將sd卡的目錄（storage目錄）獲取sd實(shí)際掛載目錄（mnt/media_rw）的權(quán)限。但是android4.4的時(shí)候vold只是寫屬性而已，然后init監(jiān)測這個(gè)屬性，屬性改變時(shí)，才會(huì)去啟動(dòng)sdcard進(jìn)程。
然后android6.0直接在vold中，fork一個(gè)進(jìn)程直接開啟sdcard進(jìn)程掛載fuse文件系統(tǒng)。并且在卸載sd的時(shí)候，在vold中卸載fuse文件系統(tǒng)。
一、掛載sd卡
下面是解析android6.0vold，掛載sd卡是的一段代碼，我們來看下。顯示掛載sd卡，然后進(jìn)行fuse操作。
if (vfat::Mount(mDevPath, mRawPath, false, false, false,// 掛載sd卡
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;
}
//creat dir by fuse before fuse action.
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;
}
dev_t before = GetDevice(mFuseWrite);
if (!(mFusePid = fork())) {
if (getMountFlags() & MountFlags::kPrimary) {
if (execl(kFusePath, kFusePath,//fuse操作
"-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";
}
}
我們再來看看fuse的代碼，也就是在sdcard中。先在main函數(shù)中獲取數(shù)據(jù)，
int main(int argc, char **argv) {
const char *source_path = NULL;
const char *label = NULL;
uid_t uid = 0;
gid_t gid = 0;
userid_t userid = 0;
bool multi_user = false;
bool full_write = false;
int i;
struct rlimit rlim;
int fs_version;
int opt;
while ((opt = getopt(argc, argv, "u:g:U:mw")) != -1) {
switch (opt) {
case 'u':
uid = strtoul(optarg, NULL, 10);
break;
case 'g':
gid = strtoul(optarg, NULL, 10);
break;
case 'U':
userid = strtoul(optarg, NULL, 10);
break;
case 'm':
multi_user = true;
break;
case 'w':
full_write = true;
break;
case '?':
default:
return usage();
}
}
for (i = optind; i < argc; i++) {
char* arg = argv[i];
if (!source_path) {
source_path = arg;
} else if (!label) {
label = arg;
} else {
ERROR("too many arguments\n");
return usage();
}
}
if (!source_path) {
ERROR("no source path specified\n");
return usage();
}
if (!label) {
ERROR("no label specified\n");
return usage();
}
if (!uid || !gid) {
ERROR("uid and gid must be nonzero\n");
return usage();
}
rlim.rlim_cur = 8192;
rlim.rlim_max = 8192;
if (setrlimit(RLIMIT_NOFILE, &rlim)) {
ERROR("Error setting RLIMIT_NOFILE, errno = %d\n", errno);
}
while ((fs_read_atomic_int("/data/.layout_version", &fs_version) == -1) || (fs_version < 3)) {
ERROR("installd fs upgrade not yet complete. Waiting...\n");
sleep(1);
}
ERROR("kangchen sdcard path:%s label:%s\n", source_path, label);
run(source_path, label, uid, gid, userid, multi_user, full_write);
return 1;
}
其中source_path就是sd卡實(shí)際掛載的地址，然后調(diào)用run函數(shù)，run函數(shù)中進(jìn)行了一些初始化，然后掛載了default，read，write 3個(gè)fuse文件系統(tǒng)，后面又開啟3個(gè)線程處理這3個(gè)文件系統(tǒng)的read，write，open等處理。
static void run(const char* source_path, const char* label, uid_t uid,
gid_t gid, userid_t userid, bool multi_user, bool full_write) {
struct fuse_global global;
struct fuse fuse_default;
struct fuse fuse_read;
struct fuse fuse_write;
struct fuse_handler handler_default;
struct fuse_handler handler_read;
struct fuse_handler handler_write;
pthread_t thread_default;
pthread_t thread_read;
pthread_t thread_write;
memset(&global, 0, sizeof(global));
memset(&fuse_default, 0, sizeof(fuse_default));
memset(&fuse_read, 0, sizeof(fuse_read));
memset(&fuse_write, 0, sizeof(fuse_write));
memset(&handler_default, 0, sizeof(handler_default));
memset(&handler_read, 0, sizeof(handler_read));
memset(&handler_write, 0, sizeof(handler_write));
pthread_mutex_init(&global.lock, NULL);
global.package_to_appid = hashmapCreate(256, str_hash, str_icase_equals);
global.uid = uid;
global.gid = gid;
global.multi_user = multi_user;
global.next_generation = 0;
global.inode_ctr = 1;
memset(&global.root, 0, sizeof(global.root));
global.root.nid = FUSE_ROOT_ID; /* 1 */
global.root.refcount = 2;
global.root.namelen = strlen(source_path);
global.root.name = strdup(source_path);
global.root.userid = userid;
global.root.uid = AID_ROOT;
global.root.under_android = false;
strcpy(global.source_path, source_path);
if (multi_user) {
global.root.perm = PERM_PRE_ROOT;
snprintf(global.obb_path, sizeof(global.obb_path), "%s/obb", source_path);
} else {
global.root.perm = PERM_ROOT;
snprintf(global.obb_path, sizeof(global.obb_path), "%s/Android/obb", source_path);
}
fuse_default.global = &global;
fuse_read.global = &global;
fuse_write.global = &global;
global.fuse_default = &fuse_default;
global.fuse_read = &fuse_read;
global.fuse_write = &fuse_write;
snprintf(fuse_default.dest_path, PATH_MAX, "/mnt/runtime/default/%s", label);
snprintf(fuse_read.dest_path, PATH_MAX, "/mnt/runtime/read/%s", label);
snprintf(fuse_write.dest_path, PATH_MAX, "/mnt/runtime/write/%s", label);
handler_default.fuse = &fuse_default;
handler_read.fuse = &fuse_read;
handler_write.fuse = &fuse_write;
handler_default.token = 0;
handler_read.token = 1;
handler_write.token = 2;
umask(0);
if (multi_user) {
/* Multi-user storage is fully isolated per user, so "other"
* permissions are completely masked off. */
if (fuse_setup(&fuse_default, AID_SDCARD_RW, 0006)
|| fuse_setup(&fuse_read, AID_EVERYBODY, 0027)
|| fuse_setup(&fuse_write, AID_EVERYBODY, full_write ? 0007 : 0027)) {
ERROR("failed to fuse_setup\n");
exit(1);
}
} else {
/* Physical storage is readable by all users on device, but
* the Android directories are masked off to a single user
* deep inside attr_from_stat(). */
if (fuse_setup(&fuse_default, AID_SDCARD_RW, 0006)
|| fuse_setup(&fuse_read, AID_EVERYBODY, full_write ? 0027 : 0022)
|| fuse_setup(&fuse_write, AID_EVERYBODY, full_write ? 0007 : 0022)) {
ERROR("failed to fuse_setup\n");
exit(1);
}
}
/* Drop privs */
if (setgroups(sizeof(kGroups) / sizeof(kGroups[0]), kGroups) < 0) {
ERROR("cannot setgroups: %s\n", strerror(errno));
exit(1);
}
if (setgid(gid) < 0) {
ERROR("cannot setgid: %s\n", strerror(errno));
exit(1);
}
if (setuid(uid) < 0) {
ERROR("cannot setuid: %s\n", strerror(errno));
exit(1);
}
if (multi_user) {
fs_prepare_dir(global.obb_path, 0775, uid, gid);
}
if (pthread_create(&thread_default, NULL, start_handler, &handler_default)
|| pthread_create(&thread_read, NULL, start_handler, &handler_read)
|| pthread_create(&thread_write, NULL, start_handler, &handler_write)) {
ERROR("failed to pthread_create\n");
exit(1);
}
watch_package_list(&global);
ERROR("terminated prematurely\n");
exit(1);
}
其中在fuse_setup中掛載了fuse文件系統(tǒng)
static int fuse_setup(struct fuse* fuse, gid_t gid, mode_t mask) {
char opts[256];
fuse->fd = open("/dev/fuse", O_RDWR);
if (fuse->fd == -1) {
ERROR("failed to open fuse device: %s\n", strerror(errno));
return -1;
}
umount2(fuse->dest_path, MNT_DETACH);
snprintf(opts, sizeof(opts),
"fd=%i,rootmode=40000,default_permissions,allow_other,user_id=%d,group_id=%d",
fuse->fd, fuse->global->uid, fuse->global->gid);
if (mount("/dev/fuse", fuse->dest_path, "fuse", MS_NOSUID | MS_NODEV | MS_NOEXEC |
MS_NOATIME, opts) != 0) {
ERROR("failed to mount fuse filesystem: %s\n", strerror(errno));
return -1;
}
fuse->gid = gid;
fuse->mask = mask;
return 0;
}
但是雖然掛載了default，read，write 3個(gè)fuse文件系統(tǒng)。
但好像只有default有用，因?yàn)樵趇nit.rc中將default目錄直接掛載到了storage，而應(yīng)用也就只能拿到storage目錄，所以只有default的fuse實(shí)際有用。
on post-fs start logd #add for amt chmod 0755 /amt # once everything is setup, no need to modify / mount rootfs rootfs / ro remount # Mount shared so changes propagate into child namespaces mount rootfs rootfs / shared rec # Mount default storage into root namespace mount none /mnt/runtime/default /storage slave bind rec
二、sd卡卸載過程
然后我們再來看看android卸載sd卡的過程，卸載sd卡的時(shí)候，是先卸載了fuse文件系統(tǒng)，然后在卸載了sd卡的mount地址。
status_t PublicVolume::doUnmount() {
if (mFusePid > 0) {
kill(mFusePid, SIGTERM);
TEMP_FAILURE_RETRY(waitpid(mFusePid, nullptr, 0));
mFusePid = 0;
}
ForceUnmount(kAsecPath);
ForceUnmount(mFuseDefault);
ForceUnmount(mFuseRead);
ForceUnmount(mFuseWrite);
ForceUnmount(mRawPath);
rmdir(mFuseDefault.c_str());
rmdir(mFuseRead.c_str());
rmdir(mFuseWrite.c_str());
rmdir(mRawPath.c_str());
mFuseDefault.clear();
mFuseRead.clear();
mFuseWrite.clear();
mRawPath.clear();
return OK;
}
總所周知，卸載sd卡mount地址的時(shí)候，會(huì)去檢查哪些進(jìn)程在使用sd卡中的文件。
如何檢查呢？是通過proc/pid下面各個(gè)文件的軟鏈接，然后通過readlink找到真正的文件地址，來判定是否正在占用sd卡中的文件。
但是在卸載fuse文件系統(tǒng)的時(shí)候，比如你有進(jìn)程在操作sd卡中的文件，這個(gè)時(shí)候操作sd卡的storage目錄會(huì)fuse到sd卡真正的掛載地址上，實(shí)際上fuse文件系統(tǒng)是在工作的，導(dǎo)致不能卸載。
但是這個(gè)時(shí)候去查找誰占用fuse文件又是查不出來的，因?yàn)槭沁M(jìn)程在操作sd卡文件，會(huì)導(dǎo)致fuse文件系統(tǒng)的操作，才會(huì)卸載不掉fuse文件系統(tǒng)。但是能找到占用的文件只能是sd卡的。
而且實(shí)際中也碰到這樣的問題，所以個(gè)人認(rèn)為應(yīng)該先kill正在使用sd卡的進(jìn)程，然后再卸載fuse文件系統(tǒng)。這樣就不會(huì)有進(jìn)程操作sd卡中的文件的時(shí)候，導(dǎo)致fuse文件系統(tǒng)也在忙而卸載不掉了。我碰到的問題是：一個(gè)如下進(jìn)程占用的sd卡文件
root@lte26007:/proc/2365/fd # ls -l lrwx------ root radio 2016-05-25 13:42 0 -> /dev/null lrwx------ root radio 2016-05-25 13:42 1 -> /dev/null lrwx------ root radio 2016-05-25 13:42 10 -> /storage/2C10-0CCC/elog/elog_20160525_134206/PHY0/test_20160525_134208_00.bin_last_0 lrwx------ root radio 2016-05-25 13:42 11 -> /storage/2C10-0CCC/elog/elog_20160525_134206/PHY0/log_up_data.dat lrwx------ root radio 2016-05-25 13:42 12 -> /storage/2C10-0CCC/elog/elog_20160525_134206/PHY1/test_20160525_134209_head.bin lrwx------ root radio 2016-05-25 13:42 13 -> /storage/2C10-0CCC/elog/elog_20160525_134206/PHY1/test_20160525_134209_00.bin_last_0 lrwx------ root radio 2016-05-25 13:42 14 -> /storage/2C10-0CCC/elog/elog_20160525_134206/PHY1/log_up_data.dat lrwx------ root radio 2016-05-25 13:42 15 -> /storage/2C10-0CCC/elog/elog_20160525_134206/PFM/test_20160525_134209_head.bin lrwx------ root radio 2016-05-25 13:42 16 -> /storage/2C10-0CCC/elog/elog_20160525_134206/PFM/test_20160525_134209_00.bin_last_0 lrwx------ root radio 2016-05-25 13:42 17 -> /storage/2C10-0CCC/elog/elog_20160525_134206/PFM/log_up_data.dat lrwx------ root radio 2016-05-25 13:42 18 -> /dev/lmi10 lrwx------ root radio 2016-05-25 13:42 19 -> /dev/TPC0 lrwx------ root radio 2016-05-25 13:42 2 -> /dev/null lrwx------ root radio 2016-05-25 13:42 20 -> /dev/modem lrwx------ root radio 2016-05-25 13:42 21 -> /dev/TPC1 lrwx------ root radio 2016-05-25 13:42 22 -> /dev/modem lrwx------ root radio 2016-05-25 13:42 23 -> /dev/lmi9 lrwx------ root radio 2016-05-25 13:42 24 -> socket:[14761] lrwx------ root radio 2016-05-25 13:42 26 -> socket:[14764] lrwx------ root radio 2016-05-25 13:42 3 -> socket:[15482] lrwx------ root radio 2016-05-25 13:42 4 -> /tmp/lc-elog.pid lrwx------ root radio 2016-05-25 13:42 5 -> /storage/2C10-0CCC/elog/elog_20160525_134206/HLS/test_20160525_134208_head.bin lrwx------ root radio 2016-05-25 13:42 6 -> /storage/2C10-0CCC/elog/elog_20160525_134206/HLS/test_20160525_134208_00.bin_last_0 lrwx------ root radio 2016-05-25 13:42 7 -> /storage/2C10-0CCC/elog/elog_20160525_134206/HLS/log_up_data.dat lrwx------ root radio 2016-05-25 13:42 8 -> /storage/2C10-0CCC/elog/elog_20160525_134206/PHY0/test_20160525_134208_head.bin lr-x------ root radio 2016-05-25 13:42 9 -> /dev/__properties__ root@lte26007:/proc/2365/fd
至于如何kill正在使用sd卡的進(jìn)程呢：
status_t PublicVolume::doUnmount() {
if (mFusePid > 0) {
kill(mFusePid, SIGTERM);
TEMP_FAILURE_RETRY(waitpid(mFusePid, nullptr, 0));
mFusePid = 0;
}
ForceUnmount(kAsecPath);
LOG(VERBOSE) << "start";
KillProcessesUsingPath(getPath());
LOG(VERBOSE) << "end";
ForceUnmount(mFuseDefault);
ForceUnmount(mFuseRead);
ForceUnmount(mFuseWrite);
ForceUnmount(mRawPath);
rmdir(mFuseDefault.c_str());
rmdir(mFuseRead.c_str());
rmdir(mFuseWrite.c_str());
rmdir(mRawPath.c_str());
mFuseDefault.clear();
mFuseRead.clear();
mFuseWrite.clear();
mRawPath.clear();
return OK;
}
可以在卸載fuse文件系統(tǒng)之前，調(diào)用KillProcessesUsingPath，來kill那些正在使用sd卡目錄的進(jìn)程。而這個(gè)mPath路徑，如果是sd卡的話，它是storage下的目錄，而不是sd卡的mount地址。如果是otg插的sd卡的話，是sd卡的mount地址，因?yàn)閛tg在storage目錄下沒有目錄，只有一個(gè)mount地址訪問，也有沒有fuse。這樣問題就解決了。
以上這篇詳談android 6.0 fuse文件系統(tǒng)的掛載和卸載問題就是小編分享給大家的全部內(nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。
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