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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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