1.启动
它是从rc文件中启动的，rc文件是second stage init才会解析的，也就是说vold主要作用做second stage mount，那first stage mount是怎么做的呢，第一阶段实际上直接调用的是fs_mgr进行的mount，fs_mgr_do_mount_one()
system/core/rootdir/init.rc
584 on early-fs
585 # Once metadata has been mounted, we'll need vold to deal with userdata checkpointing
586 start vold
2. vold main()分析 这里省略不中要的代码
cpp
65 int main(int argc, char** argv) {
....
74 LOG(DEBUG) << "Detected support for:" ---> 这里log输出内核支持的文件系统，结果来自/proc/filesystems见2.1
75 << (android::vold::IsFilesystemSupported("ext4") ? " ext4" : "")
76 << (android::vold::IsFilesystemSupported("f2fs") ? " f2fs" : "")
77 << (android::vold::IsFilesystemSupported("vfat") ? " vfat" : "")
78 << (android::vold::IsFilesystemSupported("texfat") ? " texfat" : "")
79 << (android::vold::IsFilesystemSupported("exfat") ? " exfat" : "");
80
81 VolumeManager* vm; ---> vold中两个主要的组件VolumeManager和NetlinkManager
82 NetlinkManager* nm; ---> VolumeManager负责volume的管理， NetlinkManager 负责block device uevent的管理
.........
93 mkdir("/dev/block/vold", 0755);
94
95 /* For when cryptfs checks and mounts an encrypted filesystem */
96 klog_set_level(6); ---> 设置kernel log输出level 默认是KLOG_INFO_LEVEL = 6
97
98 /* Create our singleton managers */
99 if (!(vm = VolumeManager::Instance())) { ---> 为 VolumeManager 创建实例
100 LOG(ERROR) << "Unable to create VolumeManager";
101 exit(1);
102 }
103
104 if (!(nm = NetlinkManager::Instance())) { ---> 为 NetlinkManager 创建实例
105 LOG(ERROR) << "Unable to create NetlinkManager";
106 exit(1);
107 }
108
109 if (android::base::GetBoolProperty("vold.debug", false)) { ---> vold.debug可以用来打开log， 用作显示block device uevent的发生
110 vm->setDebug(true);
111 }
112
113 if (vm->start()) { ---> VolumeManager 做初始化的操作
114 PLOG(ERROR) << "Unable to start VolumeManager";
115 exit(1);
116 }
117
118 VoldConfigs configs = {};
119 if (process_config(vm, &configs)) { ---> 获取volume的config信息, 其实config信息解析自fstab中的flags，见2.2
120 PLOG(ERROR) << "Error reading configuration... continuing anyways";
121 }
122
123 android::hardware::configureRpcThreadpool(1, false /* callerWillJoin */);
124
125 ATRACE_BEGIN("VoldNativeService::start"); ---> VoldNativeService是Ivold的实现，作为binder server，创建实例并加入到ServiceManager里
126 if (android::vold::VoldNativeService::start() != android::OK) {
127 LOG(ERROR) << "Unable to start VoldNativeService";
128 exit(1);
129 }
130 ATRACE_END();
131
132 LOG(DEBUG) << "VoldNativeService::start() completed OK";
133
134 ATRACE_BEGIN("NetlinkManager::start");
135 if (nm->start()) { ---> NetlinkManager 做初始化的操作
136 PLOG(ERROR) << "Unable to start NetlinkManager";
137 exit(1);
138 }
139 ATRACE_END();
140
141 // This call should go after listeners are started to avoid
142 // a deadlock between vold and init (see b/34278978 for details) ---> 从volume的config信息设置property
143 android::base::SetProperty("vold.has_adoptable", configs.has_adoptable ? "1" : "0");
144 android::base::SetProperty("vold.has_quota", configs.has_quota ? "1" : "0");
145 android::base::SetProperty("vold.has_reserved", configs.has_reserved ? "1" : "0");
146 android::base::SetProperty("vold.has_compress", configs.has_compress ? "1" : "0");
147
148 // Do coldboot here so it won't block booting,
149 // also the cold boot is needed in case we have flash drive
150 // connected before Vold launched
151 coldboot("/sys/block"); ---> 重新触发一下block device uevent和init进程的RegenerateUevents()类似,见2.3
152
153 ATRACE_END();
154
155 android::IPCThreadState::self()->joinThreadPool(); ------> 开启主线程 binder looper
156 LOG(INFO) << "vold shutting down";
157
158 exit(0);
159 }2.1 cat proc/filesystems nodev代表vfs， 好多啊 头大 搞那么多VFS我是真的服
nodev sysfs
nodev tmpfs
nodev bdev
nodev proc
nodev cgroup
nodev cgroup2
nodev cpuset
nodev binfmt_misc
nodev configfs
nodev debugfs
nodev tracefs
nodev securityfs
nodev sockfs
nodev bpf
nodev pipefs
nodev ramfs
nodev devpts
ext3
ext2
ext4
vfat
msdos
exfat
fuseblk
nodev fuse
nodev fusectl
nodev virtiofs
nodev overlay
nodev incremental-fs
f2fs
erofs
nodev selinuxfs
nodev binder
nodev pstore
nodev functionfs
2.2 process_config()
cpp
229 static int process_config(VolumeManager* vm, VoldConfigs* configs) {
230 ATRACE_NAME("process_config");
231
232 if (!ReadDefaultFstab(&fstab_default)) { -------> 读取fstab
233 PLOG(ERROR) << "Failed to open default fstab";
234 return -1;
235 }
236
237 /* Loop through entries looking for ones that vold manages */
238 configs->has_adoptable = false;
239 configs->has_quota = false;
240 configs->has_reserved = false;
241 configs->has_compress = false;
242 for (auto& entry : fstab_default) {
243 if (entry.fs_mgr_flags.quota) {
244 configs->has_quota = true;
245 }
246 if (entry.reserved_size > 0) {
247 configs->has_reserved = true; --------> userdata分区是有reserved size的，所以你的手机存储满了还是可以运行的
248 }
249 if (entry.fs_mgr_flags.fs_compress) {
250 configs->has_compress = true;
251 }
252
253 /* Make sure logical partitions have an updated blk_device. */
254 if (entry.fs_mgr_flags.logical && !fs_mgr_update_logical_partition(&entry) &&
255 !entry.fs_mgr_flags.no_fail) {
256 PLOG(FATAL) << "could not find logical partition " << entry.blk_device;
257 }
258
259 if (entry.mount_point == "/data" && !entry.metadata_key_dir.empty()) {
260 // Pre-populate userdata dm-devices since the uevents are asynchronous (b/198405417).
261 android::vold::defaultkey_precreate_dm_device(); ------> 这个好像有点内容，我还没看
262 }
263
264 if (entry.fs_mgr_flags.vold_managed) { ----> 就两个 /storage/sdcard1 /storage/usbotg wait,voldmanaged=sdcard1:auto
265 if (entry.fs_mgr_flags.nonremovable) {
266 LOG(WARNING) << "nonremovable no longer supported; ignoring volume";
267 continue;
268 }
269
270 std::string sysPattern(entry.blk_device);
271 std::string nickname(entry.label);
272 int flags = 0;
273
274 if (entry.is_encryptable()) {
275 flags |= android::vold::Disk::Flags::kAdoptable; ----> sdcard 作为adoptable storage， 能卡死..呵呵..笑了
276 configs->has_adoptable = true;
277 }
278 if (entry.fs_mgr_flags.no_emulated_sd ||
279 android::base::GetBoolProperty("vold.debug.default_primary", false)) {
280 flags |= android::vold::Disk::Flags::kDefaultPrimary;
281 }
282
283 vm->addDiskSource(std::shared_ptr<VolumeManager::DiskSource>( ----> 申明voldmanaged的这俩，被vm添加到了mDisksource
284 new VolumeManager::DiskSource(sysPattern, nickname, flags)));
285 }
286 }
287 return 0;
288 }2.3 do_coldboot()
cpp
188 static void do_coldboot(DIR* d, int lvl) {
189 struct dirent* de;
190 int dfd, fd;
191
192 dfd = dirfd(d);
193
194 fd = openat(dfd, "uevent", O_WRONLY | O_CLOEXEC);
195 if (fd >= 0) {
196 write(fd, "add\n", 4); --------> 因为vold启动前就已经有block device add了，所以需要重新触发 add block device uevent
197 close(fd);
198 }
199
200 while ((de = readdir(d))) {
201 DIR* d2;
202
203 if (de->d_name[0] == '.') continue;
204
205 if (de->d_type != DT_DIR && lvl > 0) continue;
206
207 fd = openat(dfd, de->d_name, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
208 if (fd < 0) continue;
209
210 d2 = fdopendir(fd);
211 if (d2 == 0)
212 close(fd);
213 else {
214 do_coldboot(d2, lvl + 1); --------> sys/block/没有找到uevent文件，递归往子目录查找
215 closedir(d2);
216 }
217 }
218 }