#include	<sys/types.h>
#include	<sys/stat.h>
#include	<fcntl.h>
#include	"ourhdr.h"

static void lockabyte(const char *, int, off_t);

int
main(void)
{
	int		fd;
	pid_t	pid;

		/* Create a file and write two bytes to it */
	if ( (fd = creat("templock", FILE_MODE)) < 0)
		err_sys("creat error");
	if (write(fd, "ab", 2) != 2)
		err_sys("write error");

	TELL_WAIT();
	if ( (pid = fork()) < 0)
		err_sys("fork error");

	else if (pid == 0) {			/* child */
		lockabyte("child", fd, 0);
		TELL_PARENT(getppid());
		WAIT_PARENT();
		lockabyte("child", fd, 1);

	} else {						/* parent */
		lockabyte("parent", fd, 1);
		TELL_CHILD(pid);
		WAIT_CHILD();
		lockabyte("parent", fd, 0);
	}
	exit(0);
}

static void
lockabyte(const char *name, int fd, off_t offset)
{
	if (writew_lock(fd, offset, SEEK_SET, 1) < 0)
		err_sys("%s: writew_lock error", name);

	printf("%s: got the lock, byte %d\n", name, offset);
}