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SubjectRe: [patch 6/9] signalfd/timerfd v3 - timerfd core ...
On Sun, 2007-03-11 at 16:13 -0700, Davide Libenzi wrote:
> On Sun, 11 Mar 2007, Davide Libenzi wrote:
> > This patch introduces a new system call for timers events delivered
> > though file descriptors. This allows timer event to be used with
> > standard POSIX poll(2), select(2) and read(2). As a consequence of
> > supporting the Linux f_op->poll subsystem, they can be used with
> > epoll(2) too.
> > The system call is defined as:
> >
> > int timerfd(int ufd, int clockid, int tmrtype, const struct timespec *utmr);
> >
> > The "ufd" parameter allows for re-use (re-programming) of an existing
> > timerfd w/out going through the close/open cycle (same as signalfd).
> > If "ufd" is -1, s new file descriptor will be created, otherwise the
> > existing "ufd" will be re-programmed.
> > The "clockid" parameter is either CLOCK_MONOTONIC or CLOCK_REALTIME.
> > The "tmrtype" parameter allows to specify the timer type. The following
> > values are supported:
> >
> > The time specified in the "utmr" parameter is a relative time
> > from NOW.
> >
> > The timer specified in the "utmr" parameter is an absolute time.
> >
> > The time specified in the "utmr" parameter is an interval at
> > which a continuous clock rate will be generated.
> >
> Duh! Forgot to update the documenation. Now timerfd() gets an itimerspec.
> For TFD_TIMER_REL only the it_interval is valid, and it's the relative
> time. For TFD_TIMER_ABS, only the it_value is valid, and that the expiry
> absolute time. For TFD_TIMER_SEQ, it_value tells when the first tick
> should be generated, and it_interval tells the period of the following
> ticks.

You should probably make it behave like the other things that use
itimerspec, just to avoid confusion -- i.e. timers are relative by
default, there's a flag that makes them absolute, they expire when
it_value specifies, and repeat every it_interval nanoseconds if
it_interval is non-zero.


int timerfd(int ufd, int clockid, int flags, const struct timespec

with TFD_TIMER_ABS in flags making the timer absolute instead of
relative (and no TFD_TIMER_REL or TFD_TIMER_SEQ at all).

Nicholas Miell <>

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