loop: 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/loop.c

@@ -2235,24 +2235,18 @@ static int loop_lookup(struct loop_device **l, int i)
 	return ret;
 }
 
-static struct kobject *loop_probe(dev_t dev, int *part, void *data)
+static void loop_probe(dev_t dev)
 {
+	int idx = MINOR(dev) >> part_shift;
 	struct loop_device *lo;
-	struct kobject *kobj;
-	int err;
+
+	if (max_loop && idx >= max_loop)
+		return;
 
 	mutex_lock(&loop_ctl_mutex);
-	err = loop_lookup(&lo, MINOR(dev) >> part_shift);
-	if (err < 0)
-		err = loop_add(&lo, MINOR(dev) >> part_shift);
-	if (err < 0)
-		kobj = NULL;
-	else
-		kobj = get_disk_and_module(lo->lo_disk);
+	if (loop_lookup(&lo, idx) < 0)
+		loop_add(&lo, idx);
 	mutex_unlock(&loop_ctl_mutex);
-
-	*part = 0;
-	return kobj;
 }
 
 static long loop_control_ioctl(struct file *file, unsigned int cmd,
@@ -2372,14 +2366,11 @@ static int __init loop_init(void)
 		goto err_out;
 
 
-	if (register_blkdev(LOOP_MAJOR, "loop")) {
+	if (__register_blkdev(LOOP_MAJOR, "loop", loop_probe)) {
 		err = -EIO;
 		goto misc_out;
 	}
 
-	blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
-				  THIS_MODULE, loop_probe, NULL, NULL);
-
 	/* pre-create number of devices given by config or max_loop */
 	mutex_lock(&loop_ctl_mutex);
 	for (i = 0; i < nr; i++)
@@ -2405,16 +2396,11 @@ static int loop_exit_cb(int id, void *ptr, void *data)
 
 static void __exit loop_exit(void)
 {
-	unsigned long range;
-
-	range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;
-
 	mutex_lock(&loop_ctl_mutex);
 
 	idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
 	idr_destroy(&loop_index_idr);
 
-	blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range);
 	unregister_blkdev(LOOP_MAJOR, "loop");
 
 	misc_deregister(&loop_misc);