+/*
+ * 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 use the two low order bits of offset to tell what is the kind of key :
+ * 00 : Private process futex (PTHREAD_PROCESS_PRIVATE)
+ * (no reference on an inode or mm)
+ * 01 : Shared futex (PTHREAD_PROCESS_SHARED)
+ * mapped on a file (reference on the underlying inode)
+ * 10 : Shared futex (PTHREAD_PROCESS_SHARED)
+ * (but private mapping on an mm, and reference taken on it)
+*/
+
+#define FUT_OFF_INODE 1 /* We set bit 0 if key has a reference on inode */
+#define FUT_OFF_MMSHARED 2 /* We set bit 1 if key has a reference on mm */
+
+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;
+};
+