#include "apue.h"#include <fcntl.h>pid_tlock_test(int fd, int type, off_t offset, int whence, off_t len){	struct flock	lock;	lock.l_type = type;		/* F_RDLCK or F_WRLCK */	lock.l_start = offset;	/* byte offset, relative to l_whence */	lock.l_whence = whence;	/* SEEK_SET, SEEK_CUR, SEEK_END */	lock.l_len = len;		/* #bytes (0 means to EOF) */	if (fcntl(fd, F_GETLK, &lock) < 0)		err_sys("fcntl error");	if (lock.l_type == F_UNLCK)		return(0);		/* false, region isn't locked by another proc */	return(lock.l_pid);	/* true, return pid of lock owner */}