1// SPDX-License-Identifier: GPL-2.0
  2
  3#define _GNU_SOURCE
  4#include <err.h>
  5#include <errno.h>
  6#include <fcntl.h>
  7#include <inttypes.h>
  8#include <limits.h>
  9#include <sched.h>
 10#include <signal.h>
 11#include <stdio.h>
 12#include <stdlib.h>
 13#include <string.h>
 14#include <sys/stat.h>
 15#include <sys/syscall.h>
 16#include <sys/types.h>
 17#include <sys/wait.h>
 18#include <unistd.h>
 19
 20#ifndef CLONE_PIDFD
 21#define CLONE_PIDFD 0x00001000
 22#endif
 23
 24#ifndef __NR_pidfd_send_signal
 25#define __NR_pidfd_send_signal -1
 26#endif
 27
 28static int do_child(void *args)
 29{
 30	printf("%d\n", getpid());
 31	_exit(EXIT_SUCCESS);
 32}
 33
 34static pid_t pidfd_clone(int flags, int *pidfd)
 35{
 36	size_t stack_size = 1024;
 37	char *stack[1024] = { 0 };
 38
 39#ifdef __ia64__
 40	return __clone2(do_child, stack, stack_size, flags | SIGCHLD, NULL, pidfd);
 41#else
 42	return clone(do_child, stack + stack_size, flags | SIGCHLD, NULL, pidfd);
 43#endif
 44}
 45
 46static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
 47					unsigned int flags)
 48{
 49	return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
 50}
 51
 52static int pidfd_metadata_fd(pid_t pid, int pidfd)
 53{
 54	int procfd, ret;
 55	char path[100];
 56
 57	snprintf(path, sizeof(path), "/proc/%d", pid);
 58	procfd = open(path, O_DIRECTORY | O_RDONLY | O_CLOEXEC);
 59	if (procfd < 0) {
 60		warn("Failed to open %s\n", path);
 61		return -1;
 62	}
 63
 64	/*
 65	 * Verify that the pid has not been recycled and our /proc/<pid> handle
 66	 * is still valid.
 67	 */
 68	ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);
 69	if (ret < 0) {
 70		switch (errno) {
 71		case EPERM:
 72			/* Process exists, just not allowed to signal it. */
 73			break;
 74		default:
 75			warn("Failed to signal process\n");
 76			close(procfd);
 77			procfd = -1;
 78		}
 79	}
 80
 81	return procfd;
 82}
 83
 84int main(int argc, char *argv[])
 85{
 86	int pidfd = -1, ret = EXIT_FAILURE;
 87	char buf[4096] = { 0 };
 88	pid_t pid;
 89	int procfd, statusfd;
 90	ssize_t bytes;
 91
 92	pid = pidfd_clone(CLONE_PIDFD, &pidfd);
 93	if (pid < 0)
 94		err(ret, "CLONE_PIDFD");
 95	if (pidfd == -1) {
 96		warnx("CLONE_PIDFD is not supported by the kernel");
 97		goto out;
 98	}
 99
100	procfd = pidfd_metadata_fd(pid, pidfd);
101	close(pidfd);
102	if (procfd < 0)
103		goto out;
104
105	statusfd = openat(procfd, "status", O_RDONLY | O_CLOEXEC);
106	close(procfd);
107	if (statusfd < 0)
108		goto out;
109
110	bytes = read(statusfd, buf, sizeof(buf));
111	if (bytes > 0)
112		bytes = write(STDOUT_FILENO, buf, bytes);
113	close(statusfd);
114	ret = EXIT_SUCCESS;
115
116out:
117	(void)wait(NULL);
118
119	exit(ret);
120}

  1// SPDX-License-Identifier: GPL-2.0
  2
  3#define _GNU_SOURCE
  4#include <err.h>
  5#include <errno.h>
  6#include <fcntl.h>
  7#include <inttypes.h>
  8#include <limits.h>
  9#include <sched.h>
 10#include <signal.h>
 11#include <stdio.h>
 12#include <stdlib.h>
 13#include <string.h>
 14#include <sys/stat.h>
 15#include <sys/syscall.h>
 16#include <sys/types.h>
 17#include <sys/wait.h>
 18#include <unistd.h>
 19
 20#ifndef CLONE_PIDFD
 21#define CLONE_PIDFD 0x00001000
 22#endif
 23
 24#ifndef __NR_pidfd_send_signal
 25#define __NR_pidfd_send_signal -1
 26#endif
 27
 28static int do_child(void *args)
 29{
 30	printf("%d\n", getpid());
 31	_exit(EXIT_SUCCESS);
 32}
 33
 34static pid_t pidfd_clone(int flags, int *pidfd)
 35{
 36	size_t stack_size = 1024;
 37	char *stack[1024] = { 0 };
 38
 39#ifdef __ia64__
 40	return __clone2(do_child, stack, stack_size, flags | SIGCHLD, NULL, pidfd);
 41#else
 42	return clone(do_child, stack + stack_size, flags | SIGCHLD, NULL, pidfd);
 43#endif
 44}
 45
 46static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
 47					unsigned int flags)
 48{
 49	return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
 50}
 51
 52static int pidfd_metadata_fd(pid_t pid, int pidfd)
 53{
 54	int procfd, ret;
 55	char path[100];
 56
 57	snprintf(path, sizeof(path), "/proc/%d", pid);
 58	procfd = open(path, O_DIRECTORY | O_RDONLY | O_CLOEXEC);
 59	if (procfd < 0) {
 60		warn("Failed to open %s\n", path);
 61		return -1;
 62	}
 63
 64	/*
 65	 * Verify that the pid has not been recycled and our /proc/<pid> handle
 66	 * is still valid.
 67	 */
 68	ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);
 69	if (ret < 0) {
 70		switch (errno) {
 71		case EPERM:
 72			/* Process exists, just not allowed to signal it. */
 73			break;
 74		default:
 75			warn("Failed to signal process\n");
 76			close(procfd);
 77			procfd = -1;
 78		}
 79	}
 80
 81	return procfd;
 82}
 83
 84int main(int argc, char *argv[])
 85{
 86	int pidfd = -1, ret = EXIT_FAILURE;
 87	char buf[4096] = { 0 };
 88	pid_t pid;
 89	int procfd, statusfd;
 90	ssize_t bytes;
 91
 92	pid = pidfd_clone(CLONE_PIDFD, &pidfd);
 93	if (pid < 0)
 94		err(ret, "CLONE_PIDFD");
 95	if (pidfd == -1) {
 96		warnx("CLONE_PIDFD is not supported by the kernel");
 97		goto out;
 98	}
 99
100	procfd = pidfd_metadata_fd(pid, pidfd);
101	close(pidfd);
102	if (procfd < 0)
103		goto out;
104
105	statusfd = openat(procfd, "status", O_RDONLY | O_CLOEXEC);
106	close(procfd);
107	if (statusfd < 0)
108		goto out;
109
110	bytes = read(statusfd, buf, sizeof(buf));
111	if (bytes > 0)
112		bytes = write(STDOUT_FILENO, buf, bytes);
113	close(statusfd);
114	ret = EXIT_SUCCESS;
115
116out:
117	(void)wait(NULL);
118
119	exit(ret);
120}