1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 79a1cea7f6ed..88b9256169f8 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -18,6 +18,17 @@ struct cpu_timer_list {
         int firing;
 };
 
+/*
+ * Bit fields within a clockid:
+ *
+ * The most significant 29 bits hold either a pid or a file descriptor.
+ *
+ * Bit 2 indicates whether a cpu clock refers to a thread or a process.
+ *
+ * Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or FD=3.
+ *
+ * A clockid is invalid if bits 2, 1, and 0 are all set.
+ */
 #define CPUCLOCK_PID(clock)             ((pid_t) ~((clock) >> 3))
 #define CPUCLOCK_PERTHREAD(clock) \
         (((clock) & (clockid_t) CPUCLOCK_PERTHREAD_MASK) != 0)
@@ -29,6 +40,8 @@ struct cpu_timer_list {
 #define CPUCLOCK_VIRT           1
 #define CPUCLOCK_SCHED          2
 #define CPUCLOCK_MAX            3
+#define CLOCKFD                 CPUCLOCK_MAX
+#define CLOCKFD_MASK            (CPUCLOCK_PERTHREAD_MASK|CPUCLOCK_CLOCK_MASK)
 
 #define MAKE_PROCESS_CPUCLOCK(pid, clock) \
         ((~(clockid_t) (pid) << 3) | (clockid_t) (clock))