btrfs: Make btrfs_find_device_by_path return struct btrfs_device

Currently this function returns an error code as well as uses one of
its arguments as a return value for struct btrfs_device. Change the
function so that it returns btrfs_device directly and use the usual
"encode error in pointer" mechanics if something goes wrong. No
functional changes.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -2108,9 +2108,8 @@ void btrfs_destroy_dev_replace_tgtdev(struct btrfs_device *tgtdev)
 	call_rcu(&tgtdev->rcu, free_device_rcu);
 }
 
-static int btrfs_find_device_by_path(struct btrfs_fs_info *fs_info,
-				     const char *device_path,
-				     struct btrfs_device **device)
+static struct btrfs_device *btrfs_find_device_by_path(
+		struct btrfs_fs_info *fs_info, const char *device_path)
 {
 	int ret = 0;
 	struct btrfs_super_block *disk_super;
@@ -2118,21 +2117,21 @@ static int btrfs_find_device_by_path(struct btrfs_fs_info *fs_info,
 	u8 *dev_uuid;
 	struct block_device *bdev;
 	struct buffer_head *bh;
+	struct btrfs_device *device;
 
-	*device = NULL;
 	ret = btrfs_get_bdev_and_sb(device_path, FMODE_READ,
 				    fs_info->bdev_holder, 0, &bdev, &bh);
 	if (ret)
-		return ret;
+		return ERR_PTR(ret);
 	disk_super = (struct btrfs_super_block *)bh->b_data;
 	devid = btrfs_stack_device_id(&disk_super->dev_item);
 	dev_uuid = disk_super->dev_item.uuid;
-	*device = btrfs_find_device(fs_info, devid, dev_uuid, disk_super->fsid);
+	device = btrfs_find_device(fs_info, devid, dev_uuid, disk_super->fsid);
 	brelse(bh);
-	if (!*device)
-		ret = -ENOENT;
+	if (!device)
+		device = ERR_PTR(-ENOENT);
 	blkdev_put(bdev, FMODE_READ);
-	return ret;
+	return device;
 }
 
 int btrfs_find_device_missing_or_by_path(struct btrfs_fs_info *fs_info,
@@ -2155,11 +2154,13 @@ int btrfs_find_device_missing_or_by_path(struct btrfs_fs_info *fs_info,
 
 		if (!*device)
 			return BTRFS_ERROR_DEV_MISSING_NOT_FOUND;
-
-		return 0;
 	} else {
-		return btrfs_find_device_by_path(fs_info, device_path, device);
+		*device = btrfs_find_device_by_path(fs_info, device_path);
+		if (IS_ERR(*device))
+			return PTR_ERR(*device);
 	}
+
+	return 0;
 }
 
 /*