build.prop 中的 property 在哪一個階段可以開始使用..

很多人很喜歡在 build.prop 中加東西。

build.prop 在 bionic/libc/include/sys/_system_properties.h :  #define PROP_PATH_SYSTEM_BUILD "/system/build.prop"

然後在 system/core/init/ 中ref...

void start_property_service(void)
{
    int fd;

    load_properties_from_file(PROP_PATH_SYSTEM_BUILD);
    load_properties_from_file(PROP_PATH_SYSTEM_DEFAULT);
    load_override_properties();
    /* Read persistent properties after all default values have been loaded. */
    load_persistent_properties();

#ifdef HAVE_SELINUX
    fd = create_socket(PROP_SERVICE_NAME, SOCK_STREAM, 0666, 0, 0, NULL);
#else
    fd = create_socket(PROP_SERVICE_NAME, SOCK_STREAM, 0666, 0, 0);
#endif
    if(fd < 0) return;
    fcntl(fd, F_SETFD, FD_CLOEXEC);
    fcntl(fd, F_SETFL, O_NONBLOCK);

    listen(fd, 8);
    property_set_fd = fd;
}

然後是在init.c :

static int property_service_init_action(int nargs, char **args)
{
    /* read any property files on system or data and
     * fire up the property service.  This must happen
     * after the ro.foo properties are set above so
     * that /data/local.prop cannot interfere with them.
     */
    start_property_service();
    return 0;
}

在 init 的 main process 中，可以看到啟動的順序：

    INFO("reading config file\n");
    init_parse_config_file("/init.rc");

    action_for_each_trigger("early-init", action_add_queue_tail);

    queue_builtin_action(wait_for_coldboot_done_action, "wait_for_coldboot_done");
    queue_builtin_action(keychord_init_action, "keychord_init");
    queue_builtin_action(console_init_action, "console_init");

    /* execute all the boot actions to get us started */
    action_for_each_trigger("init", action_add_queue_tail);

    /* skip mounting filesystems in charger mode */
    if (!is_charger) {
        action_for_each_trigger("early-fs", action_add_queue_tail);
        action_for_each_trigger("fs", action_add_queue_tail);
        action_for_each_trigger("post-fs", action_add_queue_tail);
        action_for_each_trigger("post-fs-data", action_add_queue_tail);
    }

    queue_builtin_action(property_service_init_action, "property_service_init");
    queue_builtin_action(signal_init_action, "signal_init");
    queue_builtin_action(check_startup_action, "check_startup");

    if (is_charger) {
        action_for_each_trigger("charger", action_add_queue_tail);
    } else {
        action_for_each_trigger("early-boot", action_add_queue_tail);
        action_for_each_trigger("boot", action_add_queue_tail);
    }

        /* run all property triggers based on current state of the properties */
    queue_builtin_action(queue_property_triggers_action, "queue_property_triggers");

所以在 build.prop 中的設定值，在 signal_init 階段後，就可以使用了。

---

其實從 code 來看，各個　prop 的順序是..

• /default.prop
• /system/build.prop
• /system/default.prop
• /data/local.prop

看 /system/default.prop 的產生經過...
在 android/build/ 中...依照 product_name, 會有一堆...