2 short l_type; /* F_RDLCK, F_WRLCK, or F_UNLCK */
3 short l_whence; /* flag to choose starting offset */
4 long l_start; /* relative offset, in bytes */
5 long l_len; /* length, in bytes; 0 means lock to EOF */
6 short l_pid; /* returned with F_GETLK */
7 short l_xxx; /* reserved for future use */