text: #define _GNU_SOURCE
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <signal.h>
  #include <limits.h>
  #include <unistd.h>
  #include <errno.h>
  #include <string.h>
  #include <fcntl.h>
  
  #include <linux/unistd.h>
  #include <linux/kcmp.h>
  
  #include <sys/syscall.h>
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <sys/wait.h>
  
  static long sys_kcmp(int pid1, int pid2, int type, int fd1, int fd2)
  {
  	return syscall(__NR_kcmp, pid1, pid2, type, fd1, fd2);
  }
  
  int main(int argc, char **argv)
  {
  	const char kpath[] = "kcmp-test-file";
  	int pid1, pid2;
  	int fd1, fd2;
  	int status;
  
  	fd1 = open(kpath, O_RDWR | O_CREAT | O_TRUNC, 0644);
  	pid1 = getpid();
  
  	if (fd1 < 0) {
  		perror("Can't create file");
  		exit(1);
  	}
  
  	pid2 = fork();
  	if (pid2 < 0) {
  		perror("fork failed");
  		exit(1);
  	}
  
  	if (!pid2) {
  		int pid2 = getpid();
  		int ret;
  
  		fd2 = open(kpath, O_RDWR, 0644);
  		if (fd2 < 0) {
  			perror("Can't open file");
  			exit(1);
  		}
  
  		/* An example of output and arguments */
  		printf("pid1: %6d pid2: %6d FD: %2ld FILES: %2ld VM: %2ld "
  		       "FS: %2ld SIGHAND: %2ld IO: %2ld SYSVSEM: %2ld "
  		       "INV: %2ld\n",
  		       pid1, pid2,
  		       sys_kcmp(pid1, pid2, KCMP_FILE,		fd1, fd2),
  		       sys_kcmp(pid1, pid2, KCMP_FILES,		0, 0),
  		       sys_kcmp(pid1, pid2, KCMP_VM,		0, 0),
  		       sys_kcmp(pid1, pid2, KCMP_FS,		0, 0),
  		       sys_kcmp(pid1, pid2, KCMP_SIGHAND,	0, 0),
  		       sys_kcmp(pid1, pid2, KCMP_IO,		0, 0),
  		       sys_kcmp(pid1, pid2, KCMP_SYSVSEM,	0, 0),
  
  			/* This one should fail */
  		       sys_kcmp(pid1, pid2, KCMP_TYPES + 1,	0, 0));
  
  		/* This one should return same fd */
  		ret = sys_kcmp(pid1, pid2, KCMP_FILE, fd1, fd1);
  		if (ret) {
  			printf("FAIL: 0 expected but %d returned\n", ret);
  			ret = -1;
  		} else
  			printf("PASS: 0 returned as expected\n");
  
  		/* Compare with self */
  		ret = sys_kcmp(pid1, pid1, KCMP_VM, 0, 0);
  		if (ret) {
  			printf("FAIL: 0 expected but %li returned\n", ret);
  			ret = -1;
  		} else
  			printf("PASS: 0 returned as expected\n");
  
  		exit(ret);
  	}
  
  	waitpid(pid2, &status, P_ALL);
  
  	return 0;
  }
  