brd: use __register_blkdev to allocate devices on demand

Use the simpler mechanism attached to major_name to allocate a brd device
when a currently unregistered minor is accessed.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/brd.c

@@ -426,14 +426,15 @@ static void brd_free(struct brd_device *brd)
 	kfree(brd);
 }
 
-static struct brd_device *brd_init_one(int i, bool *new)
+static void brd_probe(dev_t dev)
 {
 	struct brd_device *brd;
+	int i = MINOR(dev) / max_part;
 
-	*new = false;
+	mutex_lock(&brd_devices_mutex);
 	list_for_each_entry(brd, &brd_devices, brd_list) {
 		if (brd->brd_number == i)
-			goto out;
+			goto out_unlock;
 	}
 
 	brd = brd_alloc(i);
@@ -442,9 +443,9 @@ static struct brd_device *brd_init_one(int i, bool *new)
 		add_disk(brd->brd_disk);
 		list_add_tail(&brd->brd_list, &brd_devices);
 	}
-	*new = true;
-out:
-	return brd;
+
+out_unlock:
+	mutex_unlock(&brd_devices_mutex);
 }
 
 static void brd_del_one(struct brd_device *brd)
@@ -454,23 +455,6 @@ static void brd_del_one(struct brd_device *brd)
 	brd_free(brd);
 }
 
-static struct kobject *brd_probe(dev_t dev, int *part, void *data)
-{
-	struct brd_device *brd;
-	struct kobject *kobj;
-	bool new;
-
-	mutex_lock(&brd_devices_mutex);
-	brd = brd_init_one(MINOR(dev) / max_part, &new);
-	kobj = brd ? get_disk_and_module(brd->brd_disk) : NULL;
-	mutex_unlock(&brd_devices_mutex);
-
-	if (new)
-		*part = 0;
-
-	return kobj;
-}
-
 static inline void brd_check_and_reset_par(void)
 {
 	if (unlikely(!max_part))
@@ -510,11 +494,12 @@ static int __init brd_init(void)
 	 *	dynamically.
 	 */
 
-	if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
+	if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe))
 		return -EIO;
 
 	brd_check_and_reset_par();
 
+	mutex_lock(&brd_devices_mutex);
 	for (i = 0; i < rd_nr; i++) {
 		brd = brd_alloc(i);
 		if (!brd)
@@ -532,9 +517,7 @@ static int __init brd_init(void)
 		brd->brd_disk->queue = brd->brd_queue;
 		add_disk(brd->brd_disk);
 	}
-
-	blk_register_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS,
-				  THIS_MODULE, brd_probe, NULL, NULL);
+	mutex_unlock(&brd_devices_mutex);
 
 	pr_info("brd: module loaded\n");
 	return 0;
@@ -544,6 +527,7 @@ static int __init brd_init(void)
 		list_del(&brd->brd_list);
 		brd_free(brd);
 	}
+	mutex_unlock(&brd_devices_mutex);
 	unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
 
 	pr_info("brd: module NOT loaded !!!\n");
@@ -557,7 +541,6 @@ static void __exit brd_exit(void)
 	list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
 		brd_del_one(brd);
 
-	blk_unregister_region(MKDEV(RAMDISK_MAJOR, 0), 1UL << MINORBITS);
 	unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
 
 	pr_info("brd: module unloaded\n");