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 $NetBSD: clock_settime.2,v 1.27 2016/09/27 11:11:43 wiz Exp $

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.Dd September 23, 2016
.Dt CLOCK_SETTIME 2
.Os
.Sh NAME
.Nm clock_settime ,
.Nm clock_gettime ,
.Nm clock_getres
.Nd clock and timer functions
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
n time.h .Ft int
.Fn clock_settime "clockid_t clock_id" "const struct timespec *tp"
.Ft int
.Fn clock_gettime "clockid_t clock_id" "struct timespec *tp"
.Ft int
.Fn clock_getres "clockid_t clock_id" "struct timespec *res"
.Sh DESCRIPTION
The
.Fn clock_settime
function sets the clock identified by
.Fa clock_id
to the absolute time specified by
.Fa tp .
If the time specified by
.Fa tp
is not a multiple of the resolution of the clock,
.Fa tp
is truncated to a multiple of the resolution.

p
The
.Fn clock_gettime
function stores the time of the clock identified by
.Fa clock_id
into the location specified by
.Fa tp .

p
The
.Fn clock_getres
function stores the resolution of the clock identified by
.Fa clock_id
into the location specified by
.Fa res ,
unless
.Fa res
is
.Dv NULL .

p
The following
.Fa clock_id
values are supported:
l -tag -width CLOCK_MONOTONIC t Dv CLOCK_REALTIME identifies the realtime clock for the system.
For this clock, the values specified by
.Fn clock_settime
and obtained by
.Fn clock_gettime
represent the amount of time (in seconds and nanoseconds)
since 00:00 Universal Coordinated Time, January 1, 1970.
t Dv CLOCK_MONOTONIC identifies a clock that increases at a steady rate (monotonically).
This clock
is not affected by calls to
.Xr adjtime 2
and
.Xr settimeofday 2
and will
fail with an
.Er EINVAL
error if it's the clock specified in a call to
.Fn clock_settime .
The origin of the clock is unspecified.
t Dv CLOCK_VIRTUAL identifies a clock that increments only when the CPU is running in
user mode on behalf of the calling process.
t Dv CLOCK_PROF identifies a clock that increments when the CPU is running in user
or kernel mode on behalf of the calling process.
t Dv CLOCK_PROCESS_CPUTIME_ID identifies a per process clock based on tick values.
This clock is not settable.
t Dv CLOCK_THREAD_CPUTIME_ID identifies a per thread clock based on tick values.
This clock is not settable.
.El

p
If the calling user is not the super-user, the
.Fn clock_settime
system call will fail, and the
.Fn clock_settime
function in the standard C library will try to use the
.Xr clockctl 4
device if present, thus making it possible for non privileged users to
set the system time.
If
.Xr clockctl 4
is not present or not accessible, then
.Fn clock_settime
returns
.Er EPERM .
.Sh RETURN VALUES
A value of 0 is returned on success.
Otherwise, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn clock_settime ,
.Fn clock_gettime
and
.Fn clock_getres
functions will fail if:
l -tag -width Er t Bq Er EINVAL The
.Fa clock_id
argument does not specify a known clock.
t Bq Er ENOSYS The function is not supported by this implementation.
.El

p
The
.Fn clock_settime
function will fail if:
l -tag -width Er t Bq Er EINVAL The
.Fa tp
argument is outside the range for the specified clock,
.Fa clock_id ;
or the
.Fa tp
argument specified a nanosecond value less than zero of greater than or equal
1000 million;
or the
.Fa clock_id
argument is a clock that can not be adjusted.
t Bq Er EPERM The
calling process does not have the appropriate privilege to set the specified
clock,
.Fa clock_id .
.El

p
The
.Fn clock_gettime
function will fail if:
l -tag -width Er t Bq Er EFAULT The
.Fa tp
argument specifies an address that is not a valid part of the process address
space.
.El
.Sh SEE ALSO
.Xr ctime 3 ,
.Xr time 3 ,
 .Xr timer_gettime 3 ,
.Xr clockctl 4
.Sh STANDARDS
The
.Fn clock_settime ,
.Fn clock_gettime
and
.Fn clock_getres
functions conform to
.St -p1003.1b-93 .