inet6_option_space

INET6_OPTION_SPACE(3)    BSD 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
    
2017-02-09
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