diff --git a/include/linux/futex.h b/include/linux/futex.h
index 3f153b4..820125c 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -100,6 +100,35 @@
 extern int
 handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi);
 
+/*
+ * Futexes are matched on equal values of this key.
+ * The key type depends on whether it's a shared or private mapping.
+ * Don't rearrange members without looking at hash_futex().
+ *
+ * offset is aligned to a multiple of sizeof(u32) (== 4) by definition.
+ * We set bit 0 to indicate if it's an inode-based key.
+ */
+union futex_key {
+	struct {
+		unsigned long pgoff;
+		struct inode *inode;
+		int offset;
+	} shared;
+	struct {
+		unsigned long address;
+		struct mm_struct *mm;
+		int offset;
+	} private;
+	struct {
+		unsigned long word;
+		void *ptr;
+		int offset;
+	} both;
+};
+int get_futex_key(u32 __user *uaddr, union futex_key *key);
+void get_futex_key_refs(union futex_key *key);
+void drop_futex_key_refs(union futex_key *key);
+
 #ifdef CONFIG_FUTEX
 extern void exit_robust_list(struct task_struct *curr);
 extern void exit_pi_state_list(struct task_struct *curr);