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Diffstat (limited to 'man2/timerfd_create.2')
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diff --git a/man2/timerfd_create.2 b/man2/timerfd_create.2 deleted file mode 100644 index 1d6a0d2..0000000 --- a/man2/timerfd_create.2 +++ /dev/null @@ -1,704 +0,0 @@ -.\" Copyright (C) 2008 Michael Kerrisk <mtk.manpages@gmail.com> -.\" -.\" SPDX-License-Identifier: GPL-2.0-or-later -.\" -.TH timerfd_create 2 2023-10-31 "Linux man-pages 6.7" -.SH NAME -timerfd_create, timerfd_settime, timerfd_gettime \- -timers that notify via file descriptors -.SH LIBRARY -Standard C library -.RI ( libc ", " \-lc ) -.SH SYNOPSIS -.nf -.B #include <sys/timerfd.h> -.P -.BI "int timerfd_create(int " clockid ", int " flags ); -.P -.BI "int timerfd_settime(int " fd ", int " flags , -.BI " const struct itimerspec *" new_value , -.BI " struct itimerspec *_Nullable " old_value ); -.BI "int timerfd_gettime(int " fd ", struct itimerspec *" curr_value ); -.fi -.SH DESCRIPTION -These system calls create and operate on a timer -that delivers timer expiration notifications via a file descriptor. -They provide an alternative to the use of -.BR setitimer (2) -or -.BR timer_create (2), -with the advantage that the file descriptor may be monitored by -.BR select (2), -.BR poll (2), -and -.BR epoll (7). -.P -The use of these three system calls is analogous to the use of -.BR timer_create (2), -.BR timer_settime (2), -and -.BR timer_gettime (2). -(There is no analog of -.BR timer_getoverrun (2), -since that functionality is provided by -.BR read (2), -as described below.) -.\" -.SS timerfd_create() -.BR timerfd_create () -creates a new timer object, -and returns a file descriptor that refers to that timer. -The -.I clockid -argument specifies the clock that is used to mark the progress -of the timer, and must be one of the following: -.TP -.B CLOCK_REALTIME -A settable system-wide real-time clock. -.TP -.B CLOCK_MONOTONIC -A nonsettable monotonically increasing clock that measures time -from some unspecified point in the past that does not change -after system startup. -.TP -.BR CLOCK_BOOTTIME " (Since Linux 3.15)" -.\" commit 4a2378a943f09907fb1ae35c15de917f60289c14 -Like -.BR CLOCK_MONOTONIC , -this is a monotonically increasing clock. -However, whereas the -.B CLOCK_MONOTONIC -clock does not measure the time while a system is suspended, the -.B CLOCK_BOOTTIME -clock does include the time during which the system is suspended. -This is useful for applications that need to be suspend-aware. -.B CLOCK_REALTIME -is not suitable for such applications, since that clock is affected -by discontinuous changes to the system clock. -.TP -.BR CLOCK_REALTIME_ALARM " (since Linux 3.11)" -.\" commit 11ffa9d6065f344a9bd769a2452f26f2f671e5f8 -This clock is like -.BR CLOCK_REALTIME , -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. -.TP -.BR CLOCK_BOOTTIME_ALARM " (since Linux 3.11)" -.\" commit 11ffa9d6065f344a9bd769a2452f26f2f671e5f8 -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. -.P -See -.BR clock_getres (2) -for some further details on the above clocks. -.P -The current value of each of these clocks can be retrieved using -.BR clock_gettime (2). -.P -Starting with Linux 2.6.27, the following values may be bitwise ORed in -.I flags -to change the behavior of -.BR timerfd_create (): -.TP 14 -.B TFD_NONBLOCK -Set the -.B 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. -.P -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 . -.P -The -.I new_value -argument specifies the initial expiration and interval for the timer. -The -.I itimerspec -structure used for this argument is described in -.BR itimerspec (3type). -.P -.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. -.P -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 . -.P -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 -argument. -.P -The -.I flags -argument is a bit mask that can include the following values: -.TP -.B TFD_TIMER_ABSTIME -Interpret -.I new_value.it_value -as an absolute value on the timer's clock. -The timer will expire when the value of the timer's -clock reaches the value specified in -.IR new_value.it_value . -.TP -.B TFD_TIMER_CANCEL_ON_SET -If this flag is specified along with -.B TFD_TIMER_ABSTIME -and the clock for this timer is -.B CLOCK_REALTIME -or -.BR CLOCK_REALTIME_ALARM , -then mark this timer as cancelable if the real-time clock -undergoes a discontinuous change -.RB ( settimeofday (2), -.BR clock_settime (2), -or similar). -When such changes occur, a current or future -.BR read (2) -from the file descriptor will fail with the error -.BR ECANCELED . -.P -If the -.I old_value -argument is not NULL, then the -.I itimerspec -structure that it points to is used to return the setting of the timer -that was current at the time of the call; -see the description of -.BR timerfd_gettime () -following. -.\" -.SS timerfd_gettime() -.BR timerfd_gettime () -returns, in -.IR curr_value , -an -.I itimerspec -structure that contains the current setting of the timer -referred to by the file descriptor -.IR fd . -.P -The -.I it_value -field returns the amount of time -until the timer will next expire. -If both fields of this structure are zero, -then the timer is currently disarmed. -This field always contains a relative value, regardless of whether the -.B TFD_TIMER_ABSTIME -flag was specified when setting the timer. -.P -The -.I it_interval -field returns the interval of the timer. -If both fields of this structure are zero, -then the timer is set to expire just once, at the time specified by -.IR curr_value.it_value . -.SS Operating on a timer file descriptor -The file descriptor returned by -.BR timerfd_create () -supports the following additional operations: -.TP -.BR read (2) -If the timer has already expired one or more times since -its settings were last modified using -.BR timerfd_settime (), -or since the last successful -.BR read (2), -then the buffer given to -.BR read (2) -returns an unsigned 8-byte integer -.RI ( uint64_t ) -containing the number of expirations that have occurred. -(The returned value is in host byte order\[em]that is, -the native byte order for integers on the host machine.) -.IP -If no timer expirations have occurred at the time of the -.BR read (2), -then the call either blocks until the next timer expiration, -or fails with the error -.B EAGAIN -if the file descriptor has been made nonblocking -(via the use of the -.BR fcntl (2) -.B F_SETFL -operation to set the -.B O_NONBLOCK -flag). -.IP -A -.BR read (2) -fails with the error -.B EINVAL -if the size of the supplied buffer is less than 8 bytes. -.IP -If the associated clock is either -.B CLOCK_REALTIME -or -.BR CLOCK_REALTIME_ALARM , -the timer is absolute -.RB ( TFD_TIMER_ABSTIME ), -and the flag -.B TFD_TIMER_CANCEL_ON_SET -was specified when calling -.BR timerfd_settime (), -then -.BR read (2) -fails with the error -.B ECANCELED -if the real-time clock undergoes a discontinuous change. -(This allows the reading application to discover -such discontinuous changes to the clock.) -.IP -If the associated clock is either -.B CLOCK_REALTIME -or -.BR CLOCK_REALTIME_ALARM , -the timer is absolute -.RB ( TFD_TIMER_ABSTIME ), -and the flag -.B TFD_TIMER_CANCEL_ON_SET -was -.I not -specified when calling -.BR timerfd_settime (), -then a discontinuous negative change to the clock (e.g., -.BR clock_settime (2)) -may cause -.BR read (2) -to unblock, but return a value of 0 (i.e., no bytes read), -if the clock change occurs after the time expired, -but before the -.BR read (2) -on the file descriptor. -.TP -.BR poll (2) -.TQ -.BR select (2) -.TQ -(and similar) -The file descriptor is readable -(the -.BR select (2) -.I readfds -argument; the -.BR poll (2) -.B POLLIN -flag) -if one or more timer expirations have occurred. -.IP -The file descriptor also supports the other file-descriptor -multiplexing APIs: -.BR pselect (2), -.BR ppoll (2), -and -.BR epoll (7). -.TP -.BR ioctl (2) -The following timerfd-specific command is supported: -.RS -.TP -.BR TFD_IOC_SET_TICKS " (since Linux 3.17)" -.\" commit 5442e9fbd7c23172a1c9bc736629cd123a9923f0 -Adjust the number of timer expirations that have occurred. -The argument is a pointer to a nonzero 8-byte integer -.RI ( uint64_t *) -containing the new number of expirations. -Once the number is set, any waiter on the timer is woken up. -The only purpose of this command is to restore the expirations -for the purpose of checkpoint/restore. -This operation is available only if the kernel was configured with the -.B CONFIG_CHECKPOINT_RESTORE -option. -.RE -.TP -.BR close (2) -When the file descriptor is no longer required it should be closed. -When all file descriptors associated with the same timer object -have been closed, -the timer is disarmed and its resources are freed by the kernel. -.\" -.SS fork(2) semantics -After a -.BR fork (2), -the child inherits a copy of the file descriptor created by -.BR timerfd_create (). -The file descriptor refers to the same underlying -timer object as the corresponding file descriptor in the parent, -and -.BR read (2)s -in the child will return information about -expirations of the timer. -.\" -.SS execve(2) semantics -A file descriptor created by -.BR timerfd_create () -is preserved across -.BR execve (2), -and continues to generate timer expirations if the timer was armed. -.SH RETURN VALUE -On success, -.BR timerfd_create () -returns a new file descriptor. -On error, \-1 is returned and -.I errno -is set to indicate the error. -.P -.BR timerfd_settime () -and -.BR timerfd_gettime () -return 0 on success; -on error they return \-1, and set -.I errno -to indicate the error. -.SH ERRORS -.BR timerfd_create () -can fail with the following errors: -.TP -.B EINVAL -The -.I clockid -is not valid. -.TP -.B EINVAL -.I flags -is invalid; -or, in Linux 2.6.26 or earlier, -.I flags -is nonzero. -.TP -.B EMFILE -The per-process limit on the number of open file descriptors has been reached. -.TP -.B ENFILE -The system-wide limit on the total number of open files has been -reached. -.TP -.B ENODEV -Could not mount (internal) anonymous inode device. -.TP -.B ENOMEM -There was insufficient kernel memory to create the timer. -.TP -.B EPERM -.I clockid -was -.B CLOCK_REALTIME_ALARM -or -.B CLOCK_BOOTTIME_ALARM -but the caller did not have the -.B CAP_WAKE_ALARM -capability. -.P -.BR timerfd_settime () -and -.BR timerfd_gettime () -can fail with the following errors: -.TP -.B EBADF -.I fd -is not a valid file descriptor. -.TP -.B EFAULT -.IR new_value , -.IR old_value , -or -.I curr_value -is not a valid pointer. -.TP -.B EINVAL -.I fd -is not a valid timerfd file descriptor. -.P -.BR timerfd_settime () -can also fail with the following errors: -.TP -.B ECANCELED -See NOTES. -.TP -.B EINVAL -.I new_value -is not properly initialized (one of the -.I tv_nsec -falls outside the range zero to 999,999,999). -.TP -.B EINVAL -.\" This case only checked since Linux 2.6.29, and Linux 2.2.2[78].some-stable-version. -.\" In older kernel versions, no check was made for invalid flags. -.I flags -is invalid. -.SH STANDARDS -Linux. -.SH HISTORY -Linux 2.6.25, -glibc 2.8. -.SH NOTES -Suppose the following scenario for -.B CLOCK_REALTIME -or -.B CLOCK_REALTIME_ALARM -timer that was created with -.BR timerfd_create (): -.IP (1) 5 -The timer has been started -.RB ( timerfd_settime ()) -with the -.B TFD_TIMER_ABSTIME -and -.B TFD_TIMER_CANCEL_ON_SET -flags; -.IP (2) -A discontinuous change (e.g., -.BR settimeofday (2)) -is subsequently made to the -.B CLOCK_REALTIME -clock; and -.IP (3) -the caller once more calls -.BR timerfd_settime () -to rearm the timer (without first doing a -.BR read (2) -on the file descriptor). -.P -In this case the following occurs: -.IP \[bu] 3 -The -.BR timerfd_settime () -returns \-1 with -.I errno -set to -.BR ECANCELED . -(This enables the caller to know that the previous timer was affected -by a discontinuous change to the clock.) -.IP \[bu] -The timer -.I "is successfully rearmed" -with the settings provided in the second -.BR timerfd_settime () -call. -(This was probably an implementation accident, but won't be fixed now, -in case there are applications that depend on this behaviour.) -.SH BUGS -Currently, -.\" 2.6.29 -.BR timerfd_create () -supports fewer types of clock IDs than -.BR timer_create (2). -.SH EXAMPLES -The following program creates a timer and then monitors its progress. -The program accepts up to three command-line arguments. -The first argument specifies the number of seconds for -the initial expiration of the timer. -The second argument specifies the interval for the timer, in seconds. -The third argument specifies the number of times the program should -allow the timer to expire before terminating. -The second and third command-line arguments are optional. -.P -The following shell session demonstrates the use of the program: -.P -.in +4n -.EX -.RB "$" " a.out 3 1 100" -0.000: timer started -3.000: read: 1; total=1 -4.000: read: 1; total=2 -.BR "\[ha]Z " " # type control\-Z to suspend the program" -[1]+ Stopped ./timerfd3_demo 3 1 100 -.RB "$ " "fg" " # Resume execution after a few seconds" -a.out 3 1 100 -9.660: read: 5; total=7 -10.000: read: 1; total=8 -11.000: read: 1; total=9 -.BR "\[ha]C " " # type control\-C to suspend the program" -.EE -.in -.SS Program source -\& -.\" SRC BEGIN (timerfd_create.c) -.EX -.\" The commented out code here is what we currently need until -.\" the required stuff is in glibc -.\" -.\" -.\"/* Link with \-lrt */ -.\"#define _GNU_SOURCE -.\"#include <sys/syscall.h> -.\"#include <unistd.h> -.\"#include <time.h> -.\"#if defined(__i386__) -.\"#define __NR_timerfd_create 322 -.\"#define __NR_timerfd_settime 325 -.\"#define __NR_timerfd_gettime 326 -.\"#endif -.\" -.\"static int -.\"timerfd_create(int clockid, int flags) -.\"{ -.\" return syscall(__NR_timerfd_create, clockid, flags); -.\"} -.\" -.\"static int -.\"timerfd_settime(int fd, int flags, struct itimerspec *new_value, -.\" struct itimerspec *curr_value) -.\"{ -.\" return syscall(__NR_timerfd_settime, fd, flags, new_value, -.\" curr_value); -.\"} -.\" -.\"static int -.\"timerfd_gettime(int fd, struct itimerspec *curr_value) -.\"{ -.\" return syscall(__NR_timerfd_gettime, fd, curr_value); -.\"} -.\" -.\"#define TFD_TIMER_ABSTIME (1 << 0) -.\" -.\"//////////////////////////////////////////////////////////// -#include <err.h> -#include <inttypes.h> -#include <stdio.h> -#include <stdlib.h> -#include <sys/timerfd.h> -#include <time.h> -#include <unistd.h> -\& -static void -print_elapsed_time(void) -{ - int secs, nsecs; - static int first_call = 1; - struct timespec curr; - static struct timespec start; -\& - if (first_call) { - first_call = 0; - if (clock_gettime(CLOCK_MONOTONIC, &start) == \-1) - err(EXIT_FAILURE, "clock_gettime"); - } -\& - if (clock_gettime(CLOCK_MONOTONIC, &curr) == \-1) - err(EXIT_FAILURE, "clock_gettime"); -\& - secs = curr.tv_sec \- start.tv_sec; - nsecs = curr.tv_nsec \- start.tv_nsec; - if (nsecs < 0) { - secs\-\-; - nsecs += 1000000000; - } - printf("%d.%03d: ", secs, (nsecs + 500000) / 1000000); -} -\& -int -main(int argc, char *argv[]) -{ - int fd; - ssize_t s; - uint64_t exp, tot_exp, max_exp; - struct timespec now; - struct itimerspec new_value; -\& - if (argc != 2 && argc != 4) { - fprintf(stderr, "%s init\-secs [interval\-secs max\-exp]\en", - argv[0]); - exit(EXIT_FAILURE); - } -\& - if (clock_gettime(CLOCK_REALTIME, &now) == \-1) - err(EXIT_FAILURE, "clock_gettime"); -\& - /* Create a CLOCK_REALTIME absolute timer with initial - expiration and interval as specified in command line. */ -\& - new_value.it_value.tv_sec = now.tv_sec + atoi(argv[1]); - new_value.it_value.tv_nsec = now.tv_nsec; - if (argc == 2) { - new_value.it_interval.tv_sec = 0; - max_exp = 1; - } else { - new_value.it_interval.tv_sec = atoi(argv[2]); - max_exp = atoi(argv[3]); - } - new_value.it_interval.tv_nsec = 0; -\& - fd = timerfd_create(CLOCK_REALTIME, 0); - if (fd == \-1) - err(EXIT_FAILURE, "timerfd_create"); -\& - if (timerfd_settime(fd, TFD_TIMER_ABSTIME, &new_value, NULL) == \-1) - err(EXIT_FAILURE, "timerfd_settime"); -\& - print_elapsed_time(); - printf("timer started\en"); -\& - for (tot_exp = 0; tot_exp < max_exp;) { - s = read(fd, &exp, sizeof(uint64_t)); - if (s != sizeof(uint64_t)) - err(EXIT_FAILURE, "read"); -\& - tot_exp += exp; - print_elapsed_time(); - printf("read: %" PRIu64 "; total=%" PRIu64 "\en", exp, tot_exp); - } -\& - exit(EXIT_SUCCESS); -} -.EE -.\" SRC END -.SH SEE ALSO -.BR eventfd (2), -.BR poll (2), -.BR read (2), -.BR select (2), -.BR setitimer (2), -.BR signalfd (2), -.BR timer_create (2), -.BR timer_gettime (2), -.BR timer_settime (2), -.BR timespec (3), -.BR epoll (7), -.BR time (7) |