1#include <unistd.h>
 2#include <fcntl.h>
 3#include <errno.h>
 4
 5int lockf(int fd, int op, off_t size)
 6{
 7	struct flock l = {
 8		.l_type = F_WRLCK,
 9		.l_whence = SEEK_CUR,
10		.l_len = size,
11	};
12	switch (op) {
13	case F_TEST:
14		l.l_type = F_RDLCK;
15		if (fcntl(fd, F_GETLK, &l) < 0)
16			return -1;
17		if (l.l_type == F_UNLCK || l.l_pid == getpid())
18			return 0;
19		errno = EACCES;
20		return -1;
21	case F_ULOCK:
22		l.l_type = F_UNLCK;
23	case F_TLOCK:
24		return fcntl(fd, F_SETLK, &l);
25	case F_LOCK:
26		return fcntl(fd, F_SETLKW, &l);
27	}
28	errno = EINVAL;
29	return -1;
30}