• Davide Libenzi's avatar
    signal/timer/event: timerfd core · b215e283
    Davide Libenzi authored
    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 flags, const struct itimerspec *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
    The "clockid" parameter is either CLOCK_MONOTONIC or CLOCK_REALTIME.  The time
    specified in the "utmr->it_value" parameter is the expiry time for the timer.
    If the TFD_TIMER_ABSTIME flag is set in "flags", this is an absolute time,
    otherwise it's a relative time.
    If the time specified in the "utmr->it_interval" is not zero (.tv_sec == 0,
    tv_nsec == 0), this is the period at which the following ticks should be
    The "utmr->it_interval" should be set to zero if only one tick is requested.
    Setting the "utmr->it_value" to zero will disable the timer, or will create a
    timerfd without the timer enabled.
    The function returns the new (or same, in case "ufd" is a valid timerfd
    descriptor) file, or -1 in case of error.
    As stated before, the timerfd file descriptor supports poll(2), select(2) and
    epoll(2).  When a timer event happened on the timerfd, a POLLIN mask will be
    The read(2) call can be used, and it will return a u32 variable holding the
    number of "ticks" that happened on the interface since the last call to
    read(2).  The read(2) call supportes the O_NONBLOCK flag too, and EAGAIN will
    be returned if no ticks happened.
    A quick test program, shows timerfd working correctly on my amd64 box:
    [akpm@linux-foundation.org: add sys_timerfd to sys_ni.c]
    Signed-off-by: default avatarDavide Libenzi <davidel@xmailserver.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
timerfd.h 228 Bytes