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# inet6_option_space

    INET6_OPTION_SPACE(3)   System Library Functions Manual  INET6_OPTION_SPACE(3)

    NAME
         inet6_option_space, inet6_option_init, inet6_option_append,
         inet6_option_alloc, inet6_option_next, inet6_option_find - IPv6 Hop-by-
         Hop and Destination Options manipulation

    SYNOPSIS
         #include <netinet/in.h>

         int
         inet6_option_space(int nbytes);

         int
         inet6_option_init(void *bp, struct cmsghdr **cmsgp, int type);

         int
         inet6_option_append(struct cmsghdr *cmsg, const u_int8_t *typep,
                 int multx, int plusy);

         u_int8_t *
         inet6_option_alloc(struct cmsghdr *cmsg, int datalen, int multx,
                 int plusy);;

         int
         inet6_option_next(const struct cmsghdr *cmsg, u_int8_t **tptrp);

         int
         inet6_option_find(const struct cmsghdr *cmsg, u_int8_t **tptrp,
                 int type);

    DESCRIPTION
         Building and parsing the Hop-by-Hop and Destination options is compli-
         cated due to alignment constranints, padding and ancillary data manipula-
         tion.  RFC2292 defines a set of functions to help the application.  The
         function prototypes for these functions are all in the <netinet/in.h>
         header.

       inet6_option_space
         inet6_option_space() returns the number of bytes required to hold an
         option when it is stored as ancillary data, including the cmsghdr struc-
         ture at the beginning, and any padding at the end (to make its size a
         multiple of 8 bytes).  The argument is the size of the structure defining
         the option, which must include any pad bytes at the beginning (the value
         y in the alignment term ``xn + y''), the type byte, the length byte, and
         the option data.

         Note: If multiple options are stored in a single ancillary data object,
         which is the recommended technique, this function overestimates the
         amount of space required by the size of N-1 cmsghdr structures, where N
         is the number of options to be stored in the object.  This is of little
         consequence, since it is assumed that most Hop-by-Hop option headers and
         Destination option headers carry only one option (appendix B of
         [RFC-2460]).

       inet6_option_init
         inet6_option_init() is called once per ancillary data object that will
         contain either Hop-by-Hop or Destination options.  It returns 0 on suc-
         cess or -1 on an error.

         bp is a pointer to previously allocated space that will contain the
         ancillary data object.  It must be large enough to contain all the indi-
         vidual options to be added by later calls to inet6_option_append() and
         inet6_option_alloc().

         cmsgp is a pointer to a pointer to a cmsghdr structure.  *cmsgp is ini-
         tialized by this function to point to the cmsghdr structure constructed
         by this function in the buffer pointed to by bp.

         type is either IPV6_HOPOPTS or IPV6_DSTOPTS.  This type is stored in the
         cmsg_type member of the cmsghdr structure pointed to by *cmsgp.

       inet6_option_append
         This function appends a Hop-by-Hop option or a Destination option into an
         ancillary data object that has been initialized by inet6_option_init().
         This function returns 0 if it succeeds or -1 on an error.

         cmsg is a pointer to the cmsghdr structure that must have been initial-
         ized by inet6_option_init().

         typep is a pointer to the 8-bit option type.  It is assumed that this
         field is immediately followed by the 8-bit option data length field,
         which is then followed immediately by the option data.  The caller ini-
         tializes these three fields (the type-length-value, or TLV) before call-
         ing this function.

         The option type must have a value from 2 to 255, inclusive.  (0 and 1 are
         reserved for the Pad1 and PadN options, respectively.)

         The option data length must have a value between 0 and 255, inclusive,
         and is the length of the option data that follows.

         multx is the value x in the alignment term ``xn + y''.  It must have a
         value of 1, 2, 4, or 8.

         plusy is the value y in the alignment term ``xn + y''.  It must have a
         value between 0 and 7, inclusive.

       inet6_option_alloc
         This function appends a Hop-by-Hop option or a Destination option into an
         ancillary data object that has been initialized by inet6_option_init().
         This function returns a pointer to the 8-bit option type field that
         starts the option on success, or NULL on an error.

         The difference between this function and inet6_option_append() is that
         the latter copies the contents of a previously built option into the
         ancillary data object while the current function returns a pointer to the
         space in the data object where the option's TLV must then be built by the
         caller.

         cmsg is a pointer to the cmsghdr structure that must have been initial-
         ized by inet6_option_init().

         datalen is the value of the option data length byte for this option.
         This value is required as an argument to allow the function to determine
         if padding must be appended at the end of the option.  (The
         inet6_option_append() function does not need a data length argument since
         the option data length must already be stored by the caller.)

         multx is the value x in the alignment term ``xn + y''.  It must have a
         value of 1, 2, 4, or 8.

         plusy is the value y in the alignment term ``xn + y''.  It must have a
         value between 0 and 7, inclusive.

       inet6_option_next
         This function processes the next Hop-by-Hop option or Destination option
         in an ancillary data object.  If another option remains to be processed,
         the return value of the function is 0 and *tptrp points to the 8-bit
         option type field (which is followed by the 8-bit option data length,
         followed by the option data).  If no more options remain to be processed,
         the return value is -1 and *tptrp is NULL.  If an error occurs, the
         return value is -1 and *tptrp is not NULL.

         cmsg is a pointer to cmsghdr structure of which cmsg_level equals
         IPPROTO_IPV6 and cmsg_type equals either IPV6_HOPOPTS or IPV6_DSTOPTS.

         tptrp is a pointer to a pointer to an 8-bit byte and *tptrp is used by
         the function to remember its place in the ancillary data object each time
         the function is called.  The first time this function is called for a
         given ancillary data object, *tptrp must be set to NULL.

         Each time this function returns success, *tptrp points to the 8-bit
         option type field for the next option to be processed.

       inet6_option_find
         This function is similar to the previously described inet6_option_next()
         function, except this function lets the caller specify the option type to
         be searched for, instead of always returning the next option in the
         ancillary data object.  cmsg is a pointer to cmsghdr structure of which
         cmsg_level equals IPPROTO_IPV6 and cmsg_type equals either IPV6_HOPOPTS
         or IPV6_DSTOPTS.

         tptrp is a pointer to a pointer to an 8-bit byte and *tptrp is used by
         the function to remember its place in the ancillary data object each time
         the function is called.  The first time this function is called for a
         given ancillary data object, *tptrp must be set to NULL.  ~ This function
         starts searching for an option of the specified type beginning after the
         value of *tptrp.  If an option of the specified type is located, this
         function returns 0 and *tptrp points to the 8- bit option type field for
         the option of the specified type.  If an option of the specified type is
         not located, the return value is -1 and *tptrp is NULL.  If an error
         occurs, the return value is -1 and *tptrp is not NULL.

    DIAGNOSTICS
         inet6_option_init() and inet6_option_append() return 0 on success or -1
         on an error.

         inet6_option_alloc() returns NULL on an error.

         On errors, inet6_option_next() and inet6_option_find() return -1 setting
         *tptrp to non NULL value.

    EXAMPLES
         RFC2292 gives comprehensive examples in chapter 6.

    SEE ALSO
         W. Stevens and M. Thomas, Advanced Sockets API for IPv6, RFC2292,
         February 1998.

         S. Deering and R. Hinden, Internet Protocol, Version 6 (IPv6)
         Specification, RFC2460, December 1998.

    HISTORY
         The implementation first appeared in KAME advanced networking kit.

    STANDARDS
         The functions are documented in ``Advanced Sockets API for IPv6''
         (RFC2292).

    BUGS
         The text was shamelessly copied from RFC2292.

    BSD                            December 10, 1999                           BSD

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