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ET6_OPTION_SPACE(3)
Contents
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IN 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
#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.
RFC 2292 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 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
inet6_option_init() 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.
bp 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().
cmsgp is a pointer to a pointer to a cmsghdr structure.
*cmsgp is initialized
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 initialized
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 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.
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 initialized
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.
RFC 2292 gives comprehensive examples in chapter 6.
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.
W. Stevens and M. Thomas, Advanced Sockets API for IPv6, RFC
2292,
February 1998.
S. Deering and R. Hinden, Internet Protocol, Version 6
(IPv6)
Specification, RFC 2460, December 1998.
The functions are documented in ``Advanced Sockets API for
IPv6'' (RFC
2292).
The implementation first appeared in KAME advanced networking kit.
The text was shamelessly copied from RFC 2292.
OpenBSD 3.6 December 10, 1999
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