file_desc

    An open file descriptor obtained from a successful open, fcntl,
    or pipe function.

 request

    The operation to be performed.

 arg

    A variable that depends on the value of the request argument.

    For a request of F_DUPFD, F_SETFD, or F_SETFL, specify arg as an
    int.

    For a request of F_GETFD and F_GETFL, do not specify arg.

    For a request of F_GETLK, F_SETLK, or F_SETLKW specify arg as a
    pointer to a flock structure.