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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
- #ifndef __NR_pidfd_send_signal
- #define __NR_pidfd_send_signal -1
- #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 = -1, 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)
- err(ret, "CLONE_PIDFD");
- if (pidfd == -1) {
- warnx("CLONE_PIDFD is not supported by the kernel");
- goto out;
- }
- 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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