Btrfs: add direct I/O helper to return mirror count from extent_map.

index 6aa04e4..3dda2ce 100644
@@ -2574,10 +2574,20 @@ void btrfs_mapping_tree_free(struct btrfs_mapping_tree *tree)
 	}
 }
 
+int btrfs_map_num_copies(struct extent_map *em)
+{
+	struct map_lookup *map = (struct map_lookup *)em->bdev;
+
+	if (map->type & (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1))
+		return map->num_stripes;
+	if (map->type & BTRFS_BLOCK_GROUP_RAID10)
+		return map->sub_stripes;
+	return 1; 
+}
+
 int btrfs_num_copies(struct btrfs_mapping_tree *map_tree, u64 logical, u64 len)
 {
 	struct extent_map *em;
-	struct map_lookup *map;
 	struct extent_map_tree *em_tree = &map_tree->map_tree;
 	int ret;
 

@@ -2587,13 +2597,9 @@ int btrfs_num_copies(struct btrfs_mapping_tree *map_tree, u64 logical, u64 len)
 	BUG_ON(!em);
 
 	BUG_ON(em->start > logical || em->start + em->len < logical);
-	map = (struct map_lookup *)em->bdev;
-	if (map->type & (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1))
-		ret = map->num_stripes;
-	else if (map->type & BTRFS_BLOCK_GROUP_RAID10)
-		ret = map->sub_stripes;
-	else
-		ret = 1;
+
+	ret = btrfs_map_num_copies(em);
+
 	free_extent_map(em);
 	return ret;
 }

index 226200d..732c8c5 100644
@@ -195,4 +195,5 @@ int find_free_dev_extent(struct btrfs_trans_handle *trans,
 int btrfs_map_stripe_count(struct extent_map *em);
 struct block_device *btrfs_map_stripe_bdev(struct extent_map *em, int stripe);
 u64 btrfs_map_stripe_physical(struct extent_map *em, int stripe);
+int btrfs_map_num_copies(struct extent_map *em);
 #endif