block/genhd: port disk_scan_partitions() to file

This may run from a kernel thread via device_add_disk(). So this could
also use __fput_sync() if we were worried about EBUSY. But when it is
called from a kernel thread it's always BLK_OPEN_READ so EBUSY can't
really happen even if we do BLK_OPEN_RESTRICT_WRITES or BLK_OPEN_EXCL.

Otherwise it's called from an ioctl on the block device which is only
called from userspace and can rely on task work.

Link: https://lore.kernel.org/r/20240123-vfs-bdev-file-v2-3-adbd023e19cc@kernel.orgReviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

block/genhd.c

@@ -342,7 +342,7 @@ EXPORT_SYMBOL_GPL(disk_uevent);
 
 int disk_scan_partitions(struct gendisk *disk, blk_mode_t mode)
 {
-	struct bdev_handle *handle;
+	struct file *file;
 	int ret = 0;
 
 	if (disk->flags & (GENHD_FL_NO_PART | GENHD_FL_HIDDEN))
@@ -366,12 +366,12 @@ int disk_scan_partitions(struct gendisk *disk, blk_mode_t mode)
 	}
 
 	set_bit(GD_NEED_PART_SCAN, &disk->state);
-	handle = bdev_open_by_dev(disk_devt(disk), mode & ~BLK_OPEN_EXCL, NULL,
-				  NULL);
-	if (IS_ERR(handle))
-		ret = PTR_ERR(handle);
+	file = bdev_file_open_by_dev(disk_devt(disk), mode & ~BLK_OPEN_EXCL,
+				     NULL, NULL);
+	if (IS_ERR(file))
+		ret = PTR_ERR(file);
 	else
-		bdev_release(handle);
+		fput(file);
 
 	/*
 	 * If blkdev_get_by_dev() failed early, GD_NEED_PART_SCAN is still set,