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Diffstat (limited to 'lib/libc/sys/clock_gettime.2')
| -rw-r--r-- | lib/libc/sys/clock_gettime.2 | 168 |
1 files changed, 168 insertions, 0 deletions
diff --git a/lib/libc/sys/clock_gettime.2 b/lib/libc/sys/clock_gettime.2 new file mode 100644 index 0000000..583cc8f --- /dev/null +++ b/lib/libc/sys/clock_gettime.2 @@ -0,0 +1,168 @@ +.\" $OpenBSD: clock_gettime.2,v 1.4 1997/05/08 20:21:16 kstailey Exp $ +.\" +.\" Copyright (c) 1980, 1991, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" 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. +.\" 4. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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. +.\" +.\" $FreeBSD$ +.\" +.Dd December 29, 2009 +.Dt CLOCK_GETTIME 2 +.Os +.Sh NAME +.Nm clock_gettime , +.Nm clock_settime , +.Nm clock_getres +.Nd get/set/calibrate date and time +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In time.h +.Ft int +.Fn clock_gettime "clockid_t clock_id" "struct timespec *tp" +.Ft int +.Fn clock_settime "clockid_t clock_id" "const struct timespec *tp" +.Ft int +.Fn clock_getres "clockid_t clock_id" "struct timespec *tp" +.Sh DESCRIPTION +The +.Fn clock_gettime +and +.Fn clock_settime +system calls allow the calling process to retrieve or set the value +used by a clock which is specified by +.Fa clock_id . +.Pp +The +.Fa clock_id +argument +can be one of the following values: +.Dv CLOCK_REALTIME , +.Dv CLOCK_REALTIME_PRECISE , +.Dv CLOCK_REALTIME_FAST +for time that increments as +a wall clock should; +.Dv CLOCK_MONOTONIC , +.Dv CLOCK_MONOTONIC_PRECISE , +.Dv CLOCK_MONOTONIC_FAST +which increments in SI seconds; +.Dv CLOCK_UPTIME , +.Dv CLOCK_UPTIME_PRECISE , +.Dv CLOCK_UPTIME_FAST +which starts at zero when the kernel boots and increments +monotonically in SI seconds while the machine is running; +.Dv CLOCK_VIRTUAL +for time that increments only when +the CPU is running in user mode on behalf of the calling process; +.Dv CLOCK_PROF +for time that increments when the CPU is running in user or +kernel mode; or +.Dv CLOCK_SECOND +which returns the current second without performing a full time counter +query, using in-kernel cached value of current second. +.Pp +The clock IDs +.Fa CLOCK_REALTIME_FAST , +.Fa CLOCK_MONOTONIC_FAST , +.Fa CLOCK_UPTIME_FAST +are analogs of corresponding IDs without _FAST suffix but do not perform +a full time counter query, so their accuracy is one timer tick. +Similarly, +.Fa CLOCK_REALTIME_PRECISE , +.Fa CLOCK_MONOTONIC_PRECISE , +.Fa CLOCK_UPTIME_PRECISE +are used to get the most exact value as possible, at the expense of +execution time. +.Pp +The structure pointed to by +.Fa tp +is defined in +.In sys/timespec.h +as: +.Bd -literal +struct timespec { + time_t tv_sec; /* seconds */ + long tv_nsec; /* and nanoseconds */ +}; +.Ed +.Pp +Only the super-user may set the time of day, using only +.Fa CLOCK_REALTIME . +If the system securelevel is greater than 1 (see +.Xr init 8 ) , +the time may only be advanced. +This limitation is imposed to prevent a malicious super-user +from setting arbitrary time stamps on files. +The system time can still be adjusted backwards using the +.Xr adjtime 2 +system call even when the system is secure. +.Pp +The resolution (granularity) of a clock is returned by the +.Fn clock_getres +system call. +This value is placed in a (non-NULL) +.Fa *tp . +.Sh RETURN VALUES +.Rv -std +.Sh ERRORS +The following error codes may be set in +.Va errno : +.Bl -tag -width Er +.It Bq Er EINVAL +The +.Fa clock_id +argument +was not a valid value. +.It Bq Er EFAULT +The +.Fa *tp +argument address referenced invalid memory. +.It Bq Er EPERM +A user other than the super-user attempted to set the time. +.El +.Sh SEE ALSO +.Xr date 1 , +.Xr adjtime 2 , +.Xr ctime 3 , +.Xr timed 8 +.Sh STANDARDS +The +.Fn clock_gettime , +.Fn clock_settime , +and +.Fn clock_getres +system calls conform to +.St -p1003.1b-93 . +The clock IDs +.Fa CLOCK_REALTIME_FAST , +.Fa CLOCK_REALTIME_PRECISE , +.Fa CLOCK_MONOTONIC_FAST , +.Fa CLOCK_MONOTONIC_PRECISE , +.Fa CLOCK_UPTIME , +.Fa CLOCK_UPTIME_FAST , +.Fa CLOCK_UPTIME_PRECISE , +.Fa CLOCK_SECOND +are FreeBSD extensions to the POSIX interface. |
