安卓挂载文件系统流程

1、init进程

system/core/init/man.cpp

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int main(int argc, char** argv) { #if __has_feature(address_sanitizer)     __asan_set_error_report_callback(AsanReportCallback); #endif     // Boost prio which will be restored later     setpriority(PRIO_PROCESS, 0, -20);     if (!strcmp(basename(argv[0]), "ueventd")) {         return ueventd_main(argc, argv);     } if (argc > 1) {         if (!strcmp(argv[1], "subcontext")) {             android::base::InitLogging(argv, &android::base::KernelLogger);             const BuiltinFunctionMap& function_map = GetBuiltinFunctionMap();               return SubcontextMain(argc, argv, &function_map);         } if (!strcmp(argv[1], "selinux_setup")) {     //权限相关             return SetupSelinux(argv);         }           if (!strcmp(argv[1], "second_stage")) {         //第二阶段             return SecondStageMain(argc, argv);         }     } //第一阶段  return FirstStageMain(argc, argv); }

2、加载开机脚本init.rc

/system/core/init/init.cpp

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int SecondStageMain(int argc, char** argv) { ...... //加载开机脚本init.rc LoadBootScripts(am, sm); ...... }

解析脚本：

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static void LoadBootScripts(ActionManager& action_manager, ServiceList& service_list) {     Parser parser = CreateParser(action_manager, service_list);       std::string bootscript = GetProperty("ro.boot.init_rc", "");     if (bootscript.empty()) {         parser.ParseConfig("/system/etc/init/hw/init.rc");         if (!parser.ParseConfig("/system/etc/init")) {             late_import_paths.emplace_back("/system/etc/init");         } // late_import is available only in Q and earlier release. As we don't         // have system_ext in those versions, skip late_import for system_ext.         parser.ParseConfig("/system_ext/etc/init");         if (!parser.ParseConfig("/vendor/etc/init")) {             late_import_paths.emplace_back("/vendor/etc/init");         } if (!parser.ParseConfig("/odm/etc/init")) {             late_import_paths.emplace_back("/odm/etc/init");         }         if (!parser.ParseConfig("/product/etc/init")) {             late_import_paths.emplace_back("/product/etc/init");         } } else {         parser.ParseConfig(bootscript);     } }

3、mount_all去挂载分区mount的阶段分为mount_all --early和mount_all --late

/device/qcom/sc171/init.target.rc

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on fs     start hwservicemanager     mkdir /mnt/vendor/spunvm 0660 system system     mount_all --early     chown root system /mnt/vendor/persist     chmod 0771 /mnt/vendor/persist     restorecon_recursive /mnt/vendor/persist     mkdir /mnt/vendor/persist/data 0700 system system   on fs && property:ro.boot.product.vendor.sku=lahaina     mkdir /mnt/vendor/spunvm 0660 system system     wait /dev/block/bootdevice/by-name/spunvm     mount vfat /dev/block/bootdevice/by-name/spunvm /mnt/vendor/spunvm rw noatime shortname=lower,uid=1000,gid=1000,dmask=007,fmask=007,context=u:object_r:vendor_spunvm_file:s0   on post-fs     # set RLIMIT_MEMLOCK to 64MB     setrlimit 8 67108864 67108864   on late-fs     wait_for_prop hwservicemanager.ready true     #exec_start wait_for_keymaster     mount_all --late

/system/core/init/buildins.cpp

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{"mount_all",               {0,     kMax, {false,  do_mount_all}}}, {"mount",                   {3,     kMax, {false,  do_mount}}}, {"perform_apex_config",     {0,     0,    {false,  do_perform_apex_config}}}, {"umount",                  {1,     1,    {false,  do_umount}}}, {"umount_all",              {0,     1,    {false,  do_umount_all}}},

调用do_mount_all

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static Result<void> do_mount_all(const BuiltinArguments& args) {     auto mount_all = ParseMountAll(args.args);     if (!mount_all.ok()) return mount_all.error();       const char* prop_post_fix = "default";  bool queue_event = true;     if (mount_all->mode == MOUNT_MODE_EARLY) {         prop_post_fix = "early";         queue_event = false;     } else if (mount_all->mode == MOUNT_MODE_LATE) {         prop_post_fix = "late" }       std::string prop_name = "ro.boottime.init.mount_all."s + prop_post_fix;     android::base::Timer t;       Fstab fstab;     if (mount_all->fstab_path.empty()) {         if (!ReadDefaultFstab(&fstab)) {             return Error() << "Could not read default fstab";         } } else {         if (!ReadFstabFromFile(mount_all->fstab_path, &fstab)) {             return Error() << "Could not read fstab";         }     } //mount所有分区     auto mount_fstab_result = fs_mgr_mount_all(&fstab, mount_all->mode);     SetProperty(prop_name, std::to_string(t.duration().count()));

4、调用fs_mgr_mount_all回去解析fstab.default文件去挂载相应的分区

/system/core/fs_mgr/fs_mgr.cpp

fstab.defalut---/device/qcom/sc171/default/fstab.default

 5、mount_all --early和mount_all --late

分区是在early的阶段挂载还是在late取决于fstab.default中对于每个分区fs_mgr_flags中first_stage_mount和latemount属性的配置，

• 如果配置了first_stage_mount则在early的阶段进行挂载
• 配置了latemount则在late阶段挂载

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#<src>                                                 <mnt_point>            <type>  <mnt_flags and options>                            <fs_mgr_flags> system                                                  /system                ext4    ro,barrier=1,discard                                 wait,slotselect,avb=vbmeta_system,logical,first_stage_mount,avb_keys=/avb/q-gsi.avbpubkey:/avb/r-gsi.avbpubkey:/avb/s-gsi.avbpubkey system_ext                                              /system_ext            ext4    ro,barrier=1,discard                                 wait,slotselect,avb=vbmeta_system,logical,first_stage_mount product                                                 /product               ext4    ro,barrier=1,discard                                 wait,slotselect,avb=vbmeta_system,logical,first_stage_mount vendor                                                  /vendor                ext4    ro,barrier=1,discard                                 wait,slotselect,avb,logical,first_stage_mount odm                                                     /odm                   ext4    ro,barrier=1,discard                                 wait,slotselect,avb,logical,first_stage_mount /dev/block/by-name/metadata                             /metadata              ext4    noatime,nosuid,nodev,discard                         wait,check,formattable,first_stage_mount /dev/block/bootdevice/by-name/persist                   /mnt/vendor/persist    ext4    noatime,nosuid,nodev,barrier=1                       wait /dev/block/bootdevice/by-name/userdata                  /data                  ext4    noatime,nosuid,nodev,barrier=1,noauto_da_alloc,discard    latemount,wait,formattable,encryptable=footer,quota,reservedsize=128M /dev/block/bootdevice/by-name/misc                      /misc                  emmc    defaults                                             defaults /devices/platform/soc/8804000.sdhci/mmc_host*           /storage/sdcard1       vfat    nosuid,nodev                                         wait,voldmanaged=sdcard1:auto,encryptable=footer /devices/platform/soc/1da4000.ufshc_card/host*          /storage/sdcard1       vfat    nosuid,nodev                                         wait,voldmanaged=sdcard1:auto,encryptable=footer /*.ssusb/*.dwc3/xhci-hcd.*.auto*   /storage/usbotg        vfat    nosuid,nodev                                         wait,voldmanaged=usbotg:auto /devices/platform/soc/*.hsusb/*.dwc3/xhci-hcd.*.auto*   /storage/usbotg        vfat    nosuid,nodev                                         wait,voldmanaged=usbotg:auto /dev/block/bootdevice/by-name/modem                     /vendor/firmware_mnt   vfat    ro,shortname=lower,uid=1000,gid=1000,dmask=227,fmask=337,context=u:object_r:firmware_file:s0 wait,slotselect /dev/block/bootdevice/by-name/dsp                       /vendor/dsp            ext4    ro,nosuid,nodev,barrier=1                            wait,slotselect /dev/block/bootdevice/by-name/bluetooth                 /vendor/bt_firmware    vfat    ro,shortname=lower,uid=1002,gid=3002,dmask=227,fmask=337,context=u:object_r:bt_firmware_file:s0 wait,slotselect /dev/block/bootdevice/by-name/qmcs                      /mnt/vendor/qmcs       vfat    noatime,nosuid,nodev,context=u:object_r:vendor_qmcs_file:s0   wait,check,formattable /dev/block/bootdevice/by-name/data2                     /mnt/data2              ext4    discard                                              latemount /dev/block/bootdevice/by-name/data3                     /mnt/data3              ext4    discard                                              latemount