block: rework requesting modules for unclaimed devices

Instead of reusing the ranges in bdev_map, add a new helper that is
called if no ranges was found.  This is a first step to unpeel and
eventually remove the complex ranges structure.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -1031,6 +1031,13 @@ static ssize_t disk_badblocks_store(struct device *dev,
 	return badblocks_store(disk->bb, page, len, 0);
 }
 
+static void request_gendisk_module(dev_t devt)
+{
+	if (request_module("block-major-%d-%d", MAJOR(devt), MINOR(devt)) > 0)
+		/* Make old-style 2.4 aliases work */
+		request_module("block-major-%d", MAJOR(devt));
+}
+
 static struct gendisk *lookup_gendisk(dev_t dev, int *partno)
 {
 	struct kobject *kobj;
@@ -1055,6 +1062,14 @@ static struct gendisk *lookup_gendisk(dev_t dev, int *partno)
 		probe = p->probe;
 		best = p->range - 1;
 		*partno = dev - p->dev;
+
+		if (!probe) {
+			mutex_unlock(&bdev_map_lock);
+			module_put(owner);
+			request_gendisk_module(dev);
+			goto retry;
+		}
+
 		if (p->lock && p->lock(dev, data) < 0) {
 			module_put(owner);
 			continue;
@@ -1293,15 +1308,6 @@ static const struct seq_operations partitions_op = {
 };
 #endif
 
-
-static struct kobject *base_probe(dev_t devt, int *partno, void *data)
-{
-	if (request_module("block-major-%d-%d", MAJOR(devt), MINOR(devt)) > 0)
-		/* Make old-style 2.4 aliases work */
-		request_module("block-major-%d", MAJOR(devt));
-	return NULL;
-}
-
 static void bdev_map_init(void)
 {
 	struct bdev_map *base;
@@ -1313,7 +1319,6 @@ static void bdev_map_init(void)
 
 	base->dev = 1;
 	base->range = ~0 ;
-	base->probe = base_probe;
 	for (i = 0; i < 255; i++)
 		bdev_map[i] = base;
 }