#include <signal.h>
int pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
unsigned int flags);
Note: There is no glibc wrapper for this system call; see NOTES.
If the info argument points to a siginfo_t buffer, that buffer should be populated as described in rt_sigqueueinfo(2).
If the info argument is a NULL pointer, this is equivalent to specifying a pointer to a siginfo_t buffer whose fields match the values that are implicitly supplied when a signal is sent using kill(2):
The calling process must either be in the same PID namespace as the process referred to by pidfd, or be in an ancestor of that namespace.
The flags argument is reserved for future use; currently, this argument must be specified as 0.
The pidfd_send_signal() system call allows the avoidance of race conditions that occur when using traditional interfaces (such as 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, pidfd_send_signal() fails with the error ESRCH.
#ifndef __NR_pidfd_send_signal #define __NR_pidfd_send_signal 424 #endif
static int
pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
unsigned int flags)
{
return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
}
int
main(int argc, char *argv[])
{
siginfo_t info;
char path[PATH_MAX];
int pidfd, sig;
if (argc != 3) {
fprintf(stderr, "Usage: %s <pid> <signal>\n", 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 'siginfo_t' 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);
}