process_config解析fstab文件
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正如Linux的/etc/fstab文件，Android的开机挂载位置在特定的fstab文件中决定。vold的main函数会调用process_config对其进行解析，本例中的fstab文件为板子根目录下的fstab.rk30board文件。
fstab.rk30board
# Android fstab file.#<src> <mnt_point> <type> <mnt_flags and options> <fs_mgr_flags># The filesystem that contains the filesystem checker binary (typically /system) cannot# specify MF_CHECK, and must come before any filesystems that do specify MF_CHECK/dev/block/platform/fe330000.sdhci/by-name/system /system ext4 ro,noatime,nodiratime,noauto_da_alloc wait,resize# use this line below instead to enable verity#/dev/block/platform/fe330000.sdhci/by-name/system /system ext4 ro,noatime,nodiratime,noauto_da_alloc wait,check,verify/dev/block/platform/fe330000.sdhci/by-name/cache /cache ext4 noatime,nodiratime,nosuid,nodev,noauto_da_alloc,discard wait,check/dev/block/platform/fe330000.sdhci/by-name/metadata /metadata ext4 noatime,nodiratime,nosuid,nodev,noauto_da_alloc,discard wait,check/dev/block/platform/fe330000.sdhci/by-name/userdata /data f2fs noatime,nodiratime,nosuid,nodev,discard,inline_xattr wait,check,notrim,encryptable=/metadata/key_file#data for f2fs nobarrier#/dev/block/platform/fe330000.sdhci/by-name/userdata /data f2fs noatime,nodiratime,nosuid,nodev,discard,inline_xattr,nobarrier wait,check,notrim,encryptable=/metadata/key_file#data for ext4#/dev/block/platform/fe330000.sdhci/by-name/userdata /data ext4 noatime,nodiratime,nosuid,nodev,noauto_da_alloc,discard,errors=panic wait,check,encryptable=/metadata/key_file# sdcard/devices/platform/fe320000.dwmmc/mmc_host* auto auto defaults voldmanaged=sdcard1:auto,encryptable=userdata# for usb2.0/devices/platform/*.usb* auto vfat defaults voldmanaged=usb:auto# for usb3.0/devices/platform/usb@*/*.dwc3* auto vfat defaults voldmanaged=usb:auto /dev/block/zram0 none swap defaults zramsize=533413200DefaultFstabPath函数返回上述的fstab文件的路径。fs_mgr_read_fstab是解析的主要函数解析结果保存在结构体struct fstab中。先进入fs_mgr_read_fstab看看。
/system/vold/main.cpp
static int process_config(VolumeManager *vm) { std::string path(android::vold::DefaultFstabPath()); fstab = fs_mgr_read_fstab(path.c_str()); if (!fstab) { PLOG(ERROR) << "Failed to open default fstab " << path; return -1; } /* Loop through entries looking for ones that vold manages */ bool has_adoptable = false; for (int i = 0; i < fstab->num_entries; i++) { if (fs_mgr_is_voldmanaged(&fstab->recs[i])) { if (fs_mgr_is_nonremovable(&fstab->recs[i])) { LOG(WARNING) << "nonremovable no longer supported; ignoring volume"; continue; } std::string sysPattern(fstab->recs[i].blk_device); std::string nickname(fstab->recs[i].label); int flags = 0; if (fs_mgr_is_encryptable(&fstab->recs[i])) { flags |= android::vold::Disk::Flags::kAdoptable; has_adoptable = true; } if (fs_mgr_is_noemulatedsd(&fstab->recs[i]) || property_get_bool("vold.debug.default_primary", false)) { flags |= android::vold::Disk::Flags::kDefaultPrimary; } vm->addDiskSource(std::shared_ptr<VolumeManager::DiskSource>( new VolumeManager::DiskSource(sysPattern, nickname, flags))); } } property_set("vold.has_adoptable", has_adoptable ? "1" : "0"); return 0;} entries的值表示fstab文件中真正的挂载信息行的数量。得到entries的值后便开始初始化struct fstab结构体。struct fstab的num_entries成员初始化为entries的值，fstab_filename初始化为fstab文件路径表示的字符串，recs初始化为元素数量为num_entries的struct fstab_rec数组的指针。
接下来遍历每一个挂载信息行，逐一初始化对应的struct fstab_rec元素。正如fstab文件所示，< src>,< mnt_point>,< type>,< mnt_flags and options>,< fs_mgr_flags>标签的内容分别用来初始化struct fstab_rec的成员变量。blk_device，mount_point，fs_type的初始化比较简单，只是直接的字符串拷贝。flags和fs_mgr_flags成员需要经过parse_flags函数处理对应标签内容后才能决定。
/system/core/fs_mgr/include/fs_mgr.h
struct fstab { int num_entries; struct fstab_rec *recs; char *fstab_filename;};/system/core/fs_mgr/include/fs_mgr.h
struct fstab_rec { char *blk_device; char *mount_point; char *fs_type; unsigned long flags; char *fs_options; int fs_mgr_flags; char *key_loc; char *verity_loc; long long length; char *label; int partnum; int swap_prio; unsigned int zram_size;}; 看看parse_flags函数。考虑到不同的struct fstab_rec成员的初始化需要对parse_flags传入不同的参数实现。下面分情况讨论：
先说下flags，fs_options成员的初始化。对于< mnt_flags and options>标签项每一个以逗号为分隔的name,在mount_flags这个struct flag_list结构体数组会有对应的flag值，若没有，说明这个name是文件系统特有的。对于非文件系统特有的name，parse_flags函数会将这些name对应的flags值进行或运算返回。对于文件系统特有的name，处理方法是将它们拷贝到入参fs_options中，以逗号隔开。parse_flags函数返回到fs_mgr_read_fstab函数后，parse_flags函数的返回值用来初始化struct fstab_rec的flags成员，保存在tmp_fs_options的文件系统特有选项用来初始化fs_options成员。
再来说说剩余的其他struct fstab_rec成员的初始化。这次解析的是< fs_mgr_flags>标签项，根据name查找的依据是fs_mgr_flags的struct flag_list结构体数组。跟上段的相同，一方面，< fs_mgr_flags>标签项的的所有逗号分隔的name是用来设置flags的，另一方面，有一些name是用来初始化入参flag_vals的，具体方法见code。parse_flags函数返回到fs_mgr_read_fstab函数后，返回的flags值用来初始化struct fstab_rec的fs_mgr_flags成员。剩下的成员由入参flag_vals的对应值初始化。
/system/core/fs_mgr/fs_mgr_fstab.c
struct flag_list { const char *name; unsigned flag;};static struct flag_list mount_flags[] = { { "noatime", MS_NOATIME }, { "noexec", MS_NOEXEC }, { "nosuid", MS_NOSUID }, { "nodev", MS_NODEV }, { "nodiratime", MS_NODIRATIME }, { "ro", MS_RDONLY }, { "rw", 0 }, { "remount", MS_REMOUNT }, { "bind", MS_BIND }, { "rec", MS_REC }, { "unbindable", MS_UNBINDABLE }, { "private", MS_PRIVATE }, { "slave", MS_SLAVE }, { "shared", MS_SHARED }, { "defaults", 0 }, { 0, 0 },};static struct flag_list fs_mgr_flags[] = { { "wait", MF_WAIT }, { "check", MF_CHECK }, { "encryptable=",MF_CRYPT }, { "forceencrypt=",MF_FORCECRYPT }, { "fileencryption",MF_FILEENCRYPTION }, { "nonremovable",MF_NONREMOVABLE }, { "voldmanaged=",MF_VOLDMANAGED}, { "length=", MF_LENGTH }, { "recoveryonly",MF_RECOVERYONLY }, { "swapprio=", MF_SWAPPRIO }, { "zramsize=", MF_ZRAMSIZE }, { "verify", MF_VERIFY }, { "noemulatedsd", MF_NOEMULATEDSD }, { "notrim", MF_NOTRIM }, { "formattable", MF_FORMATTABLE }, { "defaults", 0 }, { 0, 0 },};/system/core/fs_mgr/fs_mgr_fstab.c
static int parse_flags(char *flags, struct flag_list *fl, struct fs_mgr_flag_values *flag_vals, char *fs_options, int fs_options_len){ int f = 0; int i; char *p; char *savep; /* initialize flag values. If we find a relevant flag, we'll * update the value */ if (flag_vals) { memset(flag_vals, 0, sizeof(*flag_vals)); flag_vals->partnum = -1; flag_vals->swap_prio = -1; /* negative means it wasn't specified. */ } /* initialize fs_options to the null string */ if (fs_options && (fs_options_len > 0)) { fs_options[0] = '\0'; } p = strtok_r(flags, ",", &savep); while (p) { /* Look for the flag "p" in the flag list "fl" * If not found, the loop exits with fl[i].name being null. */ for (i = 0; fl[i].name; i++) { if (!strncmp(p, fl[i].name, strlen(fl[i].name))) { f |= fl[i].flag; if ((fl[i].flag == MF_CRYPT) && flag_vals) { /* The encryptable flag is followed by an = and the * location of the keys. Get it and return it. */ flag_vals->key_loc = strdup(strchr(p, '=') + 1); } else if ((fl[i].flag == MF_VERIFY) && flag_vals) { /* If the verify flag is followed by an = and the * location for the verity state, get it and return it. */ char *start = strchr(p, '='); if (start) { flag_vals->verity_loc = strdup(start + 1); } } else if ((fl[i].flag == MF_FORCECRYPT) && flag_vals) { /* The forceencrypt flag is followed by an = and the * location of the keys. Get it and return it. */ flag_vals->key_loc = strdup(strchr(p, '=') + 1); } else if ((fl[i].flag == MF_LENGTH) && flag_vals) { /* The length flag is followed by an = and the * size of the partition. Get it and return it. */ flag_vals->part_length = strtoll(strchr(p, '=') + 1, NULL, 0); } else if ((fl[i].flag == MF_VOLDMANAGED) && flag_vals) { /* The voldmanaged flag is followed by an = and the * label, a colon and the partition number or the * word "auto", e.g. * voldmanaged=sdcard:3 * Get and return them. */ char *label_start; char *label_end; char *part_start; label_start = strchr(p, '=') + 1; label_end = strchr(p, ':'); if (label_end) { flag_vals->label = strndup(label_start, (int) (label_end - label_start)); part_start = strchr(p, ':') + 1; if (!strcmp(part_start, "auto")) { flag_vals->partnum = -1; } else { flag_vals->partnum = strtol(part_start, NULL, 0); } } else { ERROR("Warning: voldmanaged= flag malformed\n"); } } else if ((fl[i].flag == MF_SWAPPRIO) && flag_vals) { flag_vals->swap_prio = strtoll(strchr(p, '=') + 1, NULL, 0); } else if ((fl[i].flag == MF_ZRAMSIZE) && flag_vals) { int is_percent = !!strrchr(p, '%'); unsigned int val = strtoll(strchr(p, '=') + 1, NULL, 0); if (is_percent) flag_vals->zram_size = calculate_zram_size(val); else flag_vals->zram_size = val; } break; } } if (!fl[i].name) { if (fs_options) { /* It's not a known flag, so it must be a filesystem specific * option. Add it to fs_options if it was passed in. */ strlcat(fs_options, p, fs_options_len); strlcat(fs_options, ",", fs_options_len); } else { /* fs_options was not passed in, so if the flag is unknown * it's an error. */ ERROR("Warning: unknown flag %s\n", p); } } p = strtok_r(NULL, ",", &savep); } if (fs_options && fs_options[0]) { /* remove the last trailing comma from the list of options */ fs_options[strlen(fs_options) - 1] = '\0'; } return f;}/system/core/fs_mgr/fs_mgr_fstab.c
struct fstab *fs_mgr_read_fstab(const char *fstab_path){ FILE *fstab_file; int cnt, entries; ssize_t len; size_t alloc_len = 0; char *line = NULL; const char *delim = " \t"; char *save_ptr, *p; struct fstab *fstab = NULL; struct fs_mgr_flag_values flag_vals;#define FS_OPTIONS_LEN 1024 char tmp_fs_options[FS_OPTIONS_LEN]; fstab_file = fopen(fstab_path, "r"); if (!fstab_file) { ERROR("Cannot open file %s\n", fstab_path); return 0; } entries = 0; while ((len = getline(&line, &alloc_len, fstab_file)) != -1) { /* if the last character is a newline, shorten the string by 1 byte */ if (line[len - 1] == '\n') { line[len - 1] = '\0'; } /* Skip any leading whitespace */ p = line; while (isspace(*p)) { p++; } /* ignore comments or empty lines */ if (*p == '#' || *p == '\0') continue; entries++; } if (!entries) { ERROR("No entries found in fstab\n"); goto err; } /* Allocate and init the fstab structure */ fstab = calloc(1, sizeof(struct fstab)); fstab->num_entries = entries; fstab->fstab_filename = strdup(fstab_path); fstab->recs = calloc(fstab->num_entries, sizeof(struct fstab_rec)); fseek(fstab_file, 0, SEEK_SET); cnt = 0; while ((len = getline(&line, &alloc_len, fstab_file)) != -1) { /* if the last character is a newline, shorten the string by 1 byte */ if (line[len - 1] == '\n') { line[len - 1] = '\0'; } /* Skip any leading whitespace */ p = line; while (isspace(*p)) { p++; } /* ignore comments or empty lines */ if (*p == '#' || *p == '\0') continue; /* If a non-comment entry is greater than the size we allocated, give an * error and quit. This can happen in the unlikely case the file changes * between the two reads. */ if (cnt >= entries) { ERROR("Tried to process more entries than counted\n"); break; } if (!(p = strtok_r(line, delim, &save_ptr))) { ERROR("Error parsing mount source\n"); goto err; } fstab->recs[cnt].blk_device = strdup(p); if (!(p = strtok_r(NULL, delim, &save_ptr))) { ERROR("Error parsing mount_point\n"); goto err; } fstab->recs[cnt].mount_point = strdup(p); if (!(p = strtok_r(NULL, delim, &save_ptr))) { ERROR("Error parsing fs_type\n"); goto err; } fstab->recs[cnt].fs_type = strdup(p); if (!(p = strtok_r(NULL, delim, &save_ptr))) { ERROR("Error parsing mount_flags\n"); goto err; } tmp_fs_options[0] = '\0'; fstab->recs[cnt].flags = parse_flags(p, mount_flags, NULL, tmp_fs_options, FS_OPTIONS_LEN); /* fs_options are optional */ if (tmp_fs_options[0]) { fstab->recs[cnt].fs_options = strdup(tmp_fs_options); } else { fstab->recs[cnt].fs_options = NULL; } if (!(p = strtok_r(NULL, delim, &save_ptr))) { ERROR("Error parsing fs_mgr_options\n"); goto err; } fstab->recs[cnt].fs_mgr_flags = parse_flags(p, fs_mgr_flags, &flag_vals, NULL, 0); fstab->recs[cnt].key_loc = flag_vals.key_loc; fstab->recs[cnt].verity_loc = flag_vals.verity_loc; fstab->recs[cnt].length = flag_vals.part_length; fstab->recs[cnt].label = flag_vals.label; fstab->recs[cnt].partnum = flag_vals.partnum; fstab->recs[cnt].swap_prio = flag_vals.swap_prio; fstab->recs[cnt].zram_size = flag_vals.zram_size; cnt++; } fclose(fstab_file); free(line); return fstab;err: fclose(fstab_file); free(line); if (fstab) fs_mgr_free_fstab(fstab); return NULL;}回到process_config函数，现在已经得到一个表示挂载情况的struct fstab,接着处理由vold控制的挂载点(带有”voldmanaged=”标志）。根据挂载设备路径，label值（即”voldmanaged”后面’=’和’:’之间的字符串），flag值（由code逻辑得到）构建一个DiskSource对象，并push其指针到VolumeManager的mDiskSources中。vold会从这些DiskSource对象接收kernel传来的uevent事件。
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