futex: get_futex_key, get_key_refs and drop_key_refs

lguest uses the convenient futex infrastructure for inter-domain I/O, so
expose get_futex_key, get_key_refs (renamed get_futex_key_refs) and
drop_key_refs (renamed drop_futex_key_refs).  Also means we need to expose the
union that these use.

No code changes.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/include/linux/futex.h b/include/linux/futex.h
index 3f153b4e156c..820125c628c1 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -100,6 +100,35 @@ long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
 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);