struct_flock.c

struct flock {
  ......
    
  short l_type; // type of lock : F_RDLCK, F_WRLCK, F_UNLCK
                // F_RDLCK : reader's lock
                // F_WRLCK : writer's lock
                // F_UNLCK : unlock
  
  short l_whence; // SEEK_SET, SEEK_CUR, SEEK_END
  
  off_t l_start; // lock start position
  off_t l_len; // lock region length ( 0 for entire file)
  pid_t l_pid; // pid of a process that has a lock (used only in F_GETLK)
}