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// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <limits.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#ifndef CLONE_PIDFD
#define CLONE_PIDFD 0x00001000
#endif
static int do_child(void *args)
{
printf("%d\n", getpid());
_exit(EXIT_SUCCESS);
}
static pid_t pidfd_clone(int flags, int *pidfd)
{
size_t stack_size = 1024;
char *stack[1024] = { 0 };
#ifdef __ia64__
return __clone2(do_child, stack, stack_size, flags | SIGCHLD, NULL, pidfd);
#else
return clone(do_child, stack + stack_size, flags | SIGCHLD, NULL, pidfd);
#endif
}
static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
unsigned int flags)
{
return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
}
static int pidfd_metadata_fd(pid_t pid, int pidfd)
{
int procfd, ret;
char path[100];
snprintf(path, sizeof(path), "/proc/%d", pid);
procfd = open(path, O_DIRECTORY | O_RDONLY | O_CLOEXEC);
if (procfd < 0) {
warn("Failed to open %s\n", path);
return -1;
}
/*
* Verify that the pid has not been recycled and our /proc/<pid> handle
* is still valid.
*/
ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);
if (ret < 0) {
switch (errno) {
case EPERM:
/* Process exists, just not allowed to signal it. */
break;
default:
warn("Failed to signal process\n");
close(procfd);
procfd = -1;
}
}
return procfd;
}
int main(int argc, char *argv[])
{
int pidfd = 0, ret = EXIT_FAILURE;
char buf[4096] = { 0 };
pid_t pid;
int procfd, statusfd;
ssize_t bytes;
pid = pidfd_clone(CLONE_PIDFD, &pidfd);
if (pid < 0)
exit(ret);
procfd = pidfd_metadata_fd(pid, pidfd);
close(pidfd);
if (procfd < 0)
goto out;
statusfd = openat(procfd, "status", O_RDONLY | O_CLOEXEC);
close(procfd);
if (statusfd < 0)
goto out;
bytes = read(statusfd, buf, sizeof(buf));
if (bytes > 0)
bytes = write(STDOUT_FILENO, buf, bytes);
close(statusfd);
ret = EXIT_SUCCESS;
out:
(void)wait(NULL);
exit(ret);
}
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