static char *initcall_level_names[] __initdata = {
        "early",
        "core",
        "postcore",
        "arch",
        "subsys",
        "fs",
        "device",
        "late",
};

include..

#define __define_initcall(fn, id) \
        static initcall_t __initcall_##fn##id __used \
        __attribute__((__section__(".initcall" #id ".init"))) = fn

/*
 * Early initcalls run before initializing SMP.
 *
 * Only for built-in code, not modules.
 */
#define early_initcall(fn)              __define_initcall(fn, early)

/*
 * A "pure" initcall has no dependencies on anything else, and purely
 * initializes variables that couldn't be statically initialized.
 *
 * This only exists for built-in code, not for modules.
 * Keep main.c:initcall_level_names[] in sync.
 */
#define pure_initcall(fn)               __define_initcall(fn, 0)

#define core_initcall(fn)               __define_initcall(fn, 1)
#define core_initcall_sync(fn)          __define_initcall(fn, 1s)
#define postcore_initcall(fn)           __define_initcall(fn, 2)
#define postcore_initcall_sync(fn)      __define_initcall(fn, 2s)
#define arch_initcall(fn)               __define_initcall(fn, 3)
#define arch_initcall_sync(fn)          __define_initcall(fn, 3s)
#define subsys_initcall(fn)             __define_initcall(fn, 4)
#define subsys_initcall_sync(fn)        __define_initcall(fn, 4s)
#define fs_initcall(fn)                 __define_initcall(fn, 5)
#define fs_initcall_sync(fn)            __define_initcall(fn, 5s)
#define rootfs_initcall(fn)             __define_initcall(fn, rootfs)
#define device_initcall(fn)             __define_initcall(fn, 6)
#define device_initcall_sync(fn)        __define_initcall(fn, 6s)
#define late_initcall(fn)               __define_initcall(fn, 7)
#define late_initcall_sync(fn)          __define_initcall(fn, 7s)

#define __initcall(fn) device_initcall(fn)

啟動程序會依照 initcall_level_names[] 的順序把 section 內 function 一一呼叫。

所以 module 有 init function 要在啟動時被呼叫，就自己決定一下該在什麼時候，然後宣告..
以 sound_core.c 為例：

static int __init init_soundcore(void)
{
        int rc;

        rc = init_oss_soundcore();
        if (rc)
                return rc;

        sound_class = class_create(THIS_MODULE, "sound");
        if (IS_ERR(sound_class)) {
                cleanup_oss_soundcore();
                return PTR_ERR(sound_class);
        }

        sound_class->devnode = sound_devnode;

        return 0;
}

static void __exit cleanup_soundcore(void)
{
        cleanup_oss_soundcore();
        class_destroy(sound_class);
}

subsys_initcall(init_soundcore);
module_exit(cleanup_soundcore);

就可以，

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