diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c
index cf68fcf..c5715a6 100644
--- a/fs/btrfs/struct-funcs.c
+++ b/fs/btrfs/struct-funcs.c
@@ -95,3 +95,19 @@
 
 #include "ctree.h"
 
+void btrfs_node_key(struct extent_buffer *eb,
+		    struct btrfs_disk_key *disk_key, int nr)
+{
+	unsigned long ptr = btrfs_node_key_ptr_offset(nr);
+	if (eb->map_token && ptr >= eb->map_start &&
+	    ptr + sizeof(*disk_key) <= eb->map_start + eb->map_len) {
+		memcpy(disk_key, eb->kaddr + ptr - eb->map_start,
+			sizeof(*disk_key));
+		return;
+	} else if (eb->map_token) {
+		unmap_extent_buffer(eb, eb->map_token, KM_USER1);
+		eb->map_token = NULL;
+	}
+	read_eb_member(eb, (struct btrfs_key_ptr *)ptr,
+		       struct btrfs_key_ptr, key, disk_key);
+}