#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

main(int argc, char *argv[])
{
	int flight, seats, fd;
	fd = open("seatfile", O_RDWR);
	if (fd < 0) {
		perror("cannot open seatfile");
		exit(2);
	}

	if (argc != 2) {
		printf("usage: %s flight_number\n", argv[0]);
		exit(1);
	}

	flight = atoi(argv[1]);

	lseek(fd, flight*sizeof(int), SEEK_SET);
	/* lockf(fd, F_LOCK, sizeof(int)); */
	read(fd, &seats, sizeof(int));
	seats--;
	sleep(1);
	printf("%d seats remaining on flight %d\n", seats, flight);
	lseek(fd, (off_t)(flight*sizeof(int)), SEEK_SET);
	write(fd, &seats, sizeof(int));
	/* lockf(fd, F_ULOCK, -sizeof(int)); */
	close(fd);
}