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Diffstat (limited to 'man/man2/pidfd_send_signal.2')
| -rw-r--r-- | man/man2/pidfd_send_signal.2 | 240 |
1 files changed, 240 insertions, 0 deletions
diff --git a/man/man2/pidfd_send_signal.2 b/man/man2/pidfd_send_signal.2 new file mode 100644 index 000000000..205808425 --- /dev/null +++ b/man/man2/pidfd_send_signal.2 @@ -0,0 +1,240 @@ +.\" Copyright (c) 2019 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH pidfd_send_signal 2 (date) "Linux man-pages (unreleased)" +.SH NAME +pidfd_send_signal \- send a signal to a process specified by a file descriptor +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.BR "#include <linux/signal.h>" " /* Definition of " SIG* " constants */" +.BR "#include <signal.h>" " /* Definition of " SI_* " constants */" +.BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */" +.B #include <unistd.h> +.P +.BI "int syscall(SYS_pidfd_send_signal, int " pidfd ", int " sig , +.BI " siginfo_t *_Nullable " info ", unsigned int " flags ); +.fi +.P +.IR Note : +glibc provides no wrapper for +.BR pidfd_send_signal (), +necessitating the use of +.BR syscall (2). +.SH DESCRIPTION +The +.BR pidfd_send_signal () +system call sends the signal +.I sig +to the target process referred to by +.IR pidfd , +a PID file descriptor that refers to a process. +.\" See the very detailed commit message for kernel commit +.\" 3eb39f47934f9d5a3027fe00d906a45fe3a15fad +.P +If the +.I info +argument points to a +.I siginfo_t +buffer, that buffer should be populated as described in +.BR rt_sigqueueinfo (2). +.P +If the +.I info +argument is a null pointer, +this is equivalent to specifying a pointer to a +.I siginfo_t +buffer whose fields match the values that are +implicitly supplied when a signal is sent using +.BR kill (2): +.P +.PD 0 +.IP \[bu] 3 +.I si_signo +is set to the signal number; +.IP \[bu] +.I si_errno +is set to 0; +.IP \[bu] +.I si_code +is set to +.BR SI_USER ; +.IP \[bu] +.I si_pid +is set to the caller's PID; and +.IP \[bu] +.I si_uid +is set to the caller's real user ID. +.PD +.P +The calling process must either be in the same PID namespace as the +process referred to by +.IR pidfd , +or be in an ancestor of that namespace. +.P +The +.I flags +argument is reserved for future use; +currently, this argument must be specified as 0. +.SH RETURN VALUE +On success, +.BR pidfd_send_signal () +returns 0. +On error, \-1 is returned and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EBADF +.I pidfd +is not a valid PID file descriptor. +.TP +.B EINVAL +.I sig +is not a valid signal. +.TP +.B EINVAL +The calling process is not in a PID namespace from which it can +send a signal to the target process. +.TP +.B EINVAL +.I flags +is not 0. +.TP +.B EPERM +The calling process does not have permission to send the signal +to the target process. +.TP +.B EPERM +.I pidfd +doesn't refer to the calling process, and +.I info.si_code +is invalid (see +.BR rt_sigqueueinfo (2)). +.TP +.B ESRCH +The target process does not exist +(i.e., it has terminated and been waited on). +.SH STANDARDS +Linux. +.SH HISTORY +Linux 5.1. +.SH NOTES +.SS PID file descriptors +The +.I pidfd +argument is a PID file descriptor, +a file descriptor that refers to process. +Such a file descriptor can be obtained in any of the following ways: +.IP \[bu] 3 +by opening a +.IR /proc/ pid +directory; +.IP \[bu] +using +.BR pidfd_open (2); +or +.IP \[bu] +via the PID file descriptor that is returned by a call to +.BR clone (2) +or +.BR clone3 (2) +that specifies the +.B CLONE_PIDFD +flag. +.P +The +.BR pidfd_send_signal () +system call allows the avoidance of race conditions that occur +when using traditional interfaces (such as +.BR kill (2)) +to signal a process. +The problem is that the traditional interfaces specify the target process +via a process ID (PID), +with the result that the sender may accidentally send a signal to +the wrong process if the originally intended target process +has terminated and its PID has been recycled for another process. +By contrast, +a PID file descriptor is a stable reference to a specific process; +if that process terminates, +.BR pidfd_send_signal () +fails with the error +.BR ESRCH . +.SH EXAMPLES +.\" SRC BEGIN (pidfd_send_signal.c) +.EX +#define _GNU_SOURCE +#include <fcntl.h> +#include <limits.h> +#include <signal.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <sys/syscall.h> +#include <unistd.h> +\& +static int +pidfd_send_signal(int pidfd, int sig, siginfo_t *info, + unsigned int flags) +{ + return syscall(SYS_pidfd_send_signal, pidfd, sig, info, flags); +} +\& +int +main(int argc, char *argv[]) +{ + int pidfd, sig; + char path[PATH_MAX]; + siginfo_t info; +\& + if (argc != 3) { + fprintf(stderr, "Usage: %s <pid> <signal>\en", argv[0]); + exit(EXIT_FAILURE); + } +\& + sig = atoi(argv[2]); +\& + /* Obtain a PID file descriptor by opening the /proc/PID directory + of the target process. */ +\& + snprintf(path, sizeof(path), "/proc/%s", argv[1]); +\& + pidfd = open(path, O_RDONLY); + if (pidfd == \-1) { + perror("open"); + exit(EXIT_FAILURE); + } +\& + /* Populate a \[aq]siginfo_t\[aq] structure for use with + pidfd_send_signal(). */ +\& + memset(&info, 0, sizeof(info)); + info.si_code = SI_QUEUE; + info.si_signo = sig; + info.si_errno = 0; + info.si_uid = getuid(); + info.si_pid = getpid(); + info.si_value.sival_int = 1234; +\& + /* Send the signal. */ +\& + if (pidfd_send_signal(pidfd, sig, &info, 0) == \-1) { + perror("pidfd_send_signal"); + exit(EXIT_FAILURE); + } +\& + exit(EXIT_SUCCESS); +} +.EE +.\" SRC END +.SH SEE ALSO +.BR clone (2), +.BR kill (2), +.BR pidfd_open (2), +.BR rt_sigqueueinfo (2), +.BR sigaction (2), +.BR pid_namespaces (7), +.BR signal (7) |