Create Linux pidfds for several processes and dump their inode numbers.

pidfdino.c

#define _GNU_SOURCE
#include <sys/fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <wait.h>

#include <stdio.h>

static int pidfd_open(pid_t pid, unsigned flags)
{
	enum { __NR_pidfd_open = 434 };
	return syscall(__NR_pidfd_open, pid, flags);
}

int main(int argc, char *argv[])
{
	for( int i = 0; i < 10; ++i ){
		if( !fork() ){
			pid_t const pid = getpid();
			int fd = pidfd_open(pid, 0);
			struct statx st = {0};
			statx(fd, "", AT_EMPTY_PATH, STATX_TYPE|STATX_INO, &st);
			printf( "pid=%u: inode=%llu\n",
			        (unsigned)pid, (unsigned long long)st.stx_ino);
			raise(SIGSTOP);
			return 0;
		}
	}

	kill(0, SIGCONT);
	waitpid(-1, NULL, 0);

	return 0;
}