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Subject[tip:timers/core] posix-timers: Add support for fd based clocks
Commit-ID:  81e294cba2596f5f10848bbe19d98b344c2a2d5c
Gitweb: http://git.kernel.org/tip/81e294cba2596f5f10848bbe19d98b344c2a2d5c
Author: Richard Cochran <richard.cochran@omicron.at>
AuthorDate: Tue, 1 Feb 2011 13:52:32 +0000
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 2 Feb 2011 15:28:19 +0100

posix-timers: Add support for fd based clocks

Extend the negative clockids which are currently used by posix cpu
timers to encode the PID with a file descriptor based type which
encodes the fd in the upper bits.

Originally-from: Richard Cochran <richard.cochran@omicron.at>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <johnstul@us.ibm.com>
LKML-Reference: <20110201134420.062860200@linutronix.de>
---
include/linux/posix-timers.h | 13 +++++++++++++
kernel/posix-timers.c | 2 +-
2 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 79a1cea..88b9256 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))
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 5a5a4f1..df629d8 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -488,7 +488,7 @@ static void release_posix_timer(struct k_itimer *tmr, int it_id_set)
static struct k_clock *clockid_to_kclock(const clockid_t id)
{
if (id < 0)
- return &clock_posix_cpu;
+ return (id & CLOCKFD_MASK) == CLOCKFD ? NULL : &clock_posix_cpu;

if (id >= MAX_CLOCKS || !posix_clocks[id].clock_getres)
return NULL;

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