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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 vold2. vold main()分析 这里省略不中要的代码
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 sysfsnodev tmpfsnodev bdevnodev procnodev cgroupnodev cgroup2nodev cpusetnodev binfmt_miscnodev configfsnodev debugfsnodev tracefsnodev securityfsnodev sockfsnodev bpfnodev pipefsnodev ramfsnodev devptsext3ext2ext4vfatmsdosexfatfuseblknodev fusenodev fusectlnodev virtiofsnodev overlaynodev incremental-fsf2fserofsnodev selinuxfsnodev bindernodev pstorenodev functionfs
2.2 process_config()
229 static int process_config(VolumeManager* vm, VoldConfigs* configs) {230 ATRACE_NAME("process_config");231 232 if (!ReadDefaultFstab(&fstab_default)) { -------> 读取fstab233 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:auto265 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mDisksource284 new VolumeManager::DiskSource(sysPattern, nickname, flags)));285 }286 }287 return 0;288 } 2.3 do_coldboot()
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 uevent197 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 }