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this clock is like

.br clock_boottime ,

but will wake the system if it is suspended.

the caller must have the

.b cap_wake_alarm

capability in order to set a timer against this clock.

.pp

see

.br clock_getres (2)

for some further details on the above clocks.

.pp

the current value of each of these clocks can be retrieved using

.br clock_gettime (2).

.pp

starting with linux 2.6.27, the following values may be bitwise ored in

.ir flags

to change the behavior of

.br timerfd_create ():

.tp 14

.b tfd_nonblock

set the

.br o_nonblock

file status flag on the open file description (see

.br open (2))

referred to by the new file descriptor.

using this flag saves extra calls to

.br fcntl (2)

to achieve the same result.

.tp

.b tfd_cloexec

set the close-on-exec

.rb ( fd_cloexec )

flag on the new file descriptor.

see the description of the

.b o_cloexec

flag in

.br open (2)

for reasons why this may be useful.

.pp

in linux versions up to and including 2.6.26,

.i flags

must be specified as zero.

.ss timerfd_settime()

.br timerfd_settime ()

arms (starts) or disarms (stops)

the timer referred to by the file descriptor

.ir fd .

.pp

the

.i new_value

argument specifies the initial expiration and interval for the timer.

the

.i itimerspec

structure used for this argument contains two fields,

each of which is in turn a structure of type

.ir timespec :

.pp

.in +4n

.ex

struct timespec {

time_t tv_sec; /* seconds */

long tv_nsec; /* nanoseconds */

};

struct itimerspec {

struct timespec it_interval; /* interval for periodic timer */

struct timespec it_value; /* initial expiration */

};

.ee

.in

.pp

.i new_value.it_value

specifies the initial expiration of the timer,

in seconds and nanoseconds.

setting either field of

.i new_value.it_value

to a nonzero value arms the timer.

setting both fields of

.i new_value.it_value

to zero disarms the timer.

.pp

setting one or both fields of

.i new_value.it_interval

to nonzero values specifies the period, in seconds and nanoseconds,

for repeated timer expirations after the initial expiration.

if both fields of

.i new_value.it_interval

are zero, the timer expires just once, at the time specified by

.ir new_value.it_value .

.pp

by default,

the initial expiration time specified in

.i new_value

is interpreted relative to the current time

on the timer's clock at the time of the call (i.e.,

.i new_value.it_value

specifies a time relative to the current value of the clock specified by

.ir clockid ).

an absolute timeout can be selected via the

.i flags