.\" $NetBSD: clock_settime.2,v 1.27 2016/09/27 11:11:43 wiz Exp $
.\"
.\" Copyright (c) 1999 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Klaus Klein.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.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
.In 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.
.Pp
The
.Fn clock_gettime
function stores the time of the clock identified by
.Fa clock_id
into the location specified by
.Fa tp .
.Pp
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 .
.Pp
The following
.Fa clock_id
values are supported:
.Bl -tag -width CLOCK_MONOTONIC
.It 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.
.It 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.
.It Dv CLOCK_VIRTUAL
identifies a clock that increments only when the CPU is running in
user mode on behalf of the calling process.
.It Dv CLOCK_PROF
identifies a clock that increments when the CPU is running in user
or kernel mode on behalf of the calling process.
.It Dv CLOCK_PROCESS_CPUTIME_ID
identifies a per process clock based on tick values.
This clock is not settable.
.It Dv CLOCK_THREAD_CPUTIME_ID
identifies a per thread clock based on tick values.
This clock is not settable.
.El
.Pp
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:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa clock_id
argument does not specify a known clock.
.It Bq Er ENOSYS
The function is not supported by this implementation.
.El
.Pp
The
.Fn clock_settime
function will fail if:
.Bl -tag -width Er
.It 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.
.It Bq Er EPERM
The
calling process does not have the appropriate privilege to set the specified
clock,
.Fa clock_id .
.El
.Pp
The
.Fn clock_gettime
function will fail if:
.Bl -tag -width Er
.It 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 .