This is the new timerfd API as it is implemented by the following patch:
int timerfd_create(int clockid);

int timerfd_settime(int ufd, int flags,

		    const struct itimerspec *utmr,

		    struct itimerspec *otmr);

int timerfd_gettime(int ufd, struct itimerspec *otmr);
The timerfd_create() API creates an un-programmed timerfd fd. The "clockid"

parameter can be either CLOCK_MONOTONIC or CLOCK_REALTIME.

The timerfd_settime() API give new settings by the timerfd fd, by optionally

retrieving the previous expiration time (in case the "otmr" parameter is not NULL).

The time value specified in "utmr" is absolute, if the TFD_TIMER_ABSTIME bit

is set in the "flags" parameter. Otherwise it's a relative time.

The timerfd_gettime() API returns the next expiration time of the timer, or {0, 0}

if the timerfd has not been set yet.

Like the previous timerfd API implementation, read(2) and poll(2) are supported

(with the same interface).

Here's a simple test program I used to exercise the new timerfd APIs:
http://www.xmailserver.org/timerfd-test2.c
Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
- Davide
---

 fs/compat.c              |   32 ++++++-

 fs/timerfd.c             |  199 ++++++++++++++++++++++++++++++-----------------

 include/linux/compat.h   |    7 +

 include/linux/syscalls.h |    7 +

 4 files changed, 168 insertions(+), 77 deletions(-)
Index: linux-2.6.mod/fs/timerfd.c

===================================================================

--- linux-2.6.mod.orig/fs/timerfd.c	2007-09-23 15:18:09.000000000 -0700

+++ linux-2.6.mod/fs/timerfd.c	2007-09-23 15:25:55.000000000 -0700

@@ -23,15 +23,17 @@
 struct timerfd_ctx {

 	struct hrtimer tmr;

+	int clockid;

 	ktime_t tintv;

 	wait_queue_head_t wqh;

 	int expired;

+	u64 ticks;

 };
 /*

  * This gets called when the timer event triggers. We set the "expired"

  * flag, but we do not re-arm the timer (in case it's necessary,

- * tintv.tv64 != 0) until the timer is read.

+ * tintv.tv64 != 0) until...
[ message continues ]

Davide,
Can you please restructure the struct in a way which does not result in

padding by the compiler ?
struct timerfd_ctx {

	struct hrtimer tmr;

	ktime_t tintv;

	wait_queue_head_t wqh;

	u64 ticks;

	int expired;

	int clockid;
You need to use ctx->tmr.base->get_time() here, otherwise you might read
You really can avoid the goto here.
	tglx
-

Is the particular position of hrtimer_cb_get_time() in the code that would

break here? Because function was added by your patch ;)
Ack.
- Davide
-

For non high res systems we speed up the access to now by storing the

current time when we start to process the hrtimer softirq callbacks.
hrtimer_cb_get_time(timer) reads timer->base->now
For high resolution systems hrtimer_cb_get_time() resolves to

timer->base->get_time().
In the timerfd case we are not in softirq context and we read at any

given later time. Also on SMP the base->now variable might be changed by

the softirq running on the other CPU.
	tglx
-