block: factor out a part_devt helper

Add a helper to find the dev_t for a disk + partno tuple.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210525061301.2242282-8-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -1227,6 +1227,19 @@ static int __init proc_genhd_init(void)
 module_init(proc_genhd_init);
 #endif /* CONFIG_PROC_FS */
 
+dev_t part_devt(struct gendisk *disk, u8 partno)
+{
+	struct block_device *part = bdget_disk(disk, partno);
+	dev_t devt = 0;
+
+	if (part) {
+		devt = part->bd_dev;
+		bdput(part);
+	}
+
+	return devt;
+}
+
 dev_t blk_lookup_devt(const char *name, int partno)
 {
 	dev_t devt = MKDEV(0, 0);
@@ -1236,7 +1249,6 @@ dev_t blk_lookup_devt(const char *name, int partno)
 	class_dev_iter_init(&iter, &block_class, NULL, &disk_type);
 	while ((dev = class_dev_iter_next(&iter))) {
 		struct gendisk *disk = dev_to_disk(dev);
-		struct block_device *part;
 
 		if (strcmp(dev_name(dev), name))
 			continue;
@@ -1247,13 +1259,10 @@ dev_t blk_lookup_devt(const char *name, int partno)
 			 */
 			devt = MKDEV(MAJOR(dev->devt),
 				     MINOR(dev->devt) + partno);
-			break;
-		}
-		part = bdget_disk(disk, partno);
-		if (part) {
-			devt = part->bd_dev;
-			bdput(part);
-			break;
+		} else {
+			devt = part_devt(disk, partno);
+			if (devt)
+				break;
 		}
 	}
 	class_dev_iter_exit(&iter);

include/linux/genhd.h

@@ -333,6 +333,7 @@ static inline void bd_unlink_disk_holder(struct block_device *bdev,
 }
 #endif /* CONFIG_SYSFS */
 
+dev_t part_devt(struct gendisk *disk, u8 partno);
 dev_t blk_lookup_devt(const char *name, int partno);
 void blk_request_module(dev_t devt);
 #ifdef CONFIG_BLOCK

init/do_mounts.c

@@ -133,14 +133,8 @@ static dev_t devt_from_partuuid(const char *uuid_str)
 		 * Attempt to find the requested partition by adding an offset
 		 * to the partition number found by UUID.
 		 */
-		struct block_device *part;
-
-		part = bdget_disk(dev_to_disk(dev),
-				  dev_to_bdev(dev)->bd_partno + offset);
-		if (part) {
-			devt = part->bd_dev;
-			bdput(part);
-		}
+		devt = part_devt(dev_to_disk(dev),
+				 dev_to_bdev(dev)->bd_partno + offset);
 	} else {
 		devt = dev->devt;
 	}