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INET6_OPTION_SPACE(3)
Contents
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inet6_option_space, inet6_option_init, inet6_option_append,
inet6_option_alloc, inet6_option_next, inet6_option_find -- IPv6 Hop-byHop
and Destination Options manipulation
Standard C Library (libc, -lc)
#include <sys/types.h>
#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);
Building and parsing the Hop-by-Hop and Destination options is complicated
due to alignment constraints, padding and ancillary data manipulation.
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
The inet6_option_space() function returns the number of bytes required to
hold an option when it is stored as ancillary data, including the cmsghdr
structure 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
The inet6_option_init() function is called once per ancillary data object
that will contain either Hop-by-Hop or Destination options. It returns 0
on success or -1 on an error.
The bp argument is a pointer to previously allocated space that will contain
the ancillary data object. It must be large enough to contain all
the individual options to be added by later calls to
inet6_option_append() and inet6_option_alloc().
The cmsgp argument is a pointer to a pointer to a cmsghdr structure. The
*cmsgp argument is initialized by this function to point to the cmsghdr
structure constructed by this function in the buffer pointed to by bp.
The type argument 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.
The cmsg argument is a pointer to the cmsghdr structure that must have
been initialized by inet6_option_init().
The typep argument 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
initializes these three fields (the type-length-value, or TLV) before
calling 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.
The multx argument is the value x in the alignment term ``xn + y''. It
must have a value of 1, 2, 4, or 8.
The plusy argument 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.
The cmsg argument is a pointer to the cmsghdr structure that must have
been initialized by inet6_option_init().
The datalen argument 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.)
The multx argument is the value x in the alignment term ``xn + y''. It
must have a value of 1, 2, 4, or 8.
The plusy argument 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.
The cmsg argument is a pointer to cmsghdr structure of which cmsg_level
equals IPPROTO_IPV6 and cmsg_type equals either IPV6_HOPOPTS or
IPV6_DSTOPTS.
The tptrp argument 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. The cmsg argument is a pointer to cmsghdr structure
of which cmsg_level equals IPPROTO_IPV6 and cmsg_type equals either
IPV6_HOPOPTS or IPV6_DSTOPTS.
The tptrp argument 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.
The inet6_option_init() and inet6_option_append() functions return 0 on
success or -1 on an error.
The inet6_option_alloc() function returns NULL on an error.
On errors, inet6_option_next() and inet6_option_find() return -1 setting
*tptrp to non NULL value.
RFC2292 gives comprehensive examples in chapter 6.
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.
The implementation first appeared in KAME advanced networking kit.
The functions are documented in ``Advanced Sockets API for IPv6''
(RFC2292).
The text was shamelessly copied from RFC2292.
FreeBSD 5.2.1 December 10, 1999 FreeBSD 5.2.1 [ Back ] |
