futex: make clock selectable for FUTEX_WAIT_BITSET

FUTEX_WAIT_BITSET could be used instead of FUTEX_WAIT by setting the
bit set to FUTEX_BITSET_MATCH_ANY, but FUTEX_WAIT uses CLOCK_REALTIME
while FUTEX_WAIT_BITSET uses CLOCK_MONOTONIC.

Add a flag to select CLOCK_REALTIME for FUTEX_WAIT_BITSET so glibc can
replace the FUTEX_WAIT logic which needs to do gettimeofday() calls
before and after the syscall to convert the absolute timeout to a
relative timeout for FUTEX_WAIT.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Ulrich Drepper <drepper@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/futex.h b/include/linux/futex.h
index 8f627b9ae2b1..3bf5bb5a34f9 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -25,7 +25,8 @@ union ktime;
 #define FUTEX_WAKE_BITSET       10
 
 #define FUTEX_PRIVATE_FLAG      128
-#define FUTEX_CMD_MASK          ~FUTEX_PRIVATE_FLAG
+#define FUTEX_CLOCK_REALTIME    256
+#define FUTEX_CMD_MASK          ~(FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)
 
 #define FUTEX_WAIT_PRIVATE      (FUTEX_WAIT | FUTEX_PRIVATE_FLAG)
 #define FUTEX_WAKE_PRIVATE      (FUTEX_WAKE | FUTEX_PRIVATE_FLAG)