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Dd December 10, 1999
Dt INET6_OPTION_SPACE 3
Os
\"
Sh NAME
Nm inet6_option_space ,
Nm inet6_option_init ,
Nm inet6_option_append ,
Nm inet6_option_alloc ,
Nm inet6_option_next ,
Nm inet6_option_find
Nd IPv6 Hop-by-Hop and Destination Options manipulation
\"
Sh SYNOPSIS
In netinet/in.h
Ft "int"
Fn inet6_option_space "int nbytes"
Ft "int"
Fn inet6_option_init "void *bp" "struct cmsghdr **cmsgp" "int type"
Ft "int"
Fn inet6_option_append "struct cmsghdr *cmsg" "const uint8_t *typep" "int multx" "int plusy"
Ft "uint8_t *"
Fn inet6_option_alloc "struct cmsghdr *cmsg" "int datalen" "int multx" "int plusy"
Ft "int"
Fn inet6_option_next "const struct cmsghdr *cmsg" "uint8_t **tptrp"
Ft "int"
Fn inet6_option_find "const struct cmsghdr *cmsg" "uint8_t **tptrp" "int type"
\"
Sh DESCRIPTION
\"
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
In netinet/in.h
header.
\"
Ss inet6_option_space
Fn inet6_option_space
returns the number of bytes required to hold an option when it is stored as
ancillary data, including the
Li cmsghdr
structure at the beginning,
and any padding at the end
Po
to make its size a multiple of 8 bytes
Pc .
The argument is the size of the structure defining the option,
which must include any pad bytes at the beginning
Po
the value
Li y
in the alignment term
Dq Li xn + y
Pc ,
the type byte, the length byte, and the option data.
Pp
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
Li N-1
Li cmsghdr
structures,
where
Li 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
Pq appendix B of [RFC 2460] .
\"
Ss inet6_option_init
Fn inet6_option_init
is called once per ancillary data object that will
contain either Hop-by-Hop or Destination options.
It returns
Li 0
on success or
Li -1
on an error.
Pp
Fa 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
Fn inet6_option_append
and
Fn inet6_option_alloc .
Pp
Fa cmsgp
is a pointer to a pointer to a
Li cmsghdr
structure.
Fa *cmsgp
is initialized by this function to point to the
Li cmsghdr
structure constructed by this function in the buffer pointed to by
Fa bp .
Pp
Fa type
is either
Dv IPV6_HOPOPTS
or
Dv IPV6_DSTOPTS .
This
Fa type
is stored in the
Li cmsg_type
member of the
Li cmsghdr
structure pointed to by
Fa *cmsgp .
\"
Ss 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
Fn inet6_option_init .
This function returns
Li 0
if it succeeds or
Li -1
on an error.
Pp
Fa cmsg
is a pointer to the
Li cmsghdr
structure that must have been
initialized by
Fn inet6_option_init .
Pp
Fa 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
Pq the type-length-value, or TLV
before calling this function.
Pp
The option type must have a value from
Li 2
to
Li 255 ,
inclusive.
Po
Li 0
and
Li 1
are reserved for the
Li Pad1
and
Li PadN
options, respectively.
Pc
Pp
The option data length must have a value between
Li 0
and
Li 255 ,
inclusive, and is the length of the option data that follows.
Pp
Fa multx
is the value
Li x
in the alignment term
Dq Li xn + y .
It must have a value of
Li 1 ,
Li 2 ,
Li 4 ,
or
Li 8 .
Pp
Fa plusy
is the value
Li y
in the alignment term
Dq Li xn + y .
It must have a value between
Li 0
and
Li 7 ,
inclusive.
\"
Ss 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
Fn inet6_option_init .
This function returns a pointer to the 8-bit
option type field that starts the option on success, or
Dv NULL
on an error.
Pp
The difference between this function and
Fn 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.
Pp
Fa cmsg
is a pointer to the
Li cmsghdr
structure that must have been
initialized by
Fn inet6_option_init .
Pp
Fa 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.
Po
The
Fn inet6_option_append
function does not need a data length argument
since the option data length must already be stored by the caller.
Pc
Pp
Fa multx
is the value
Li x
in the alignment term
Dq Li xn + y .
It must have a value of
Li 1 ,
Li 2 ,
Li 4 ,
or
Li 8 .
Pp
Fa plusy
is the value
Li y
in the alignment term
Dq Li xn + y .
It must have a value between
Li 0
and
Li 7 ,
inclusive.
\"
Ss 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
Li 0
and
Fa *tptrp
points to
the 8-bit option type field
Po
which is followed by the 8-bit option
data length, followed by the option data
Pc .
If no more options remain
to be processed, the return value is
Li -1
and
Fa *tptrp
is
Dv NULL .
If an error occurs, the return value is
Li -1
and
Fa *tptrp
is not
Dv NULL .
Pp
Fa cmsg
is a pointer to
Li cmsghdr
structure of which
Li cmsg_level
equals
Dv IPPROTO_IPV6
and
Li cmsg_type
equals either
Dv IPV6_HOPOPTS
or
Dv IPV6_DSTOPTS .
Pp
Fa tptrp
is a pointer to a pointer to an 8-bit byte and
Fa *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,
Fa *tptrp
must be set to
Dv NULL .
Pp
Each time this function returns success,
Fa *tptrp
points to the 8-bit
option type field for the next option to be processed.
\"
Ss inet6_option_find
This function is similar to the previously described
Fn 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.
Fa cmsg
is a
pointer to
Li cmsghdr
structure of which
Li cmsg_level
equals
Dv IPPROTO_IPV6
and
Li cmsg_type
equals either
Dv IPV6_HOPOPTS
or
Dv IPV6_DSTOPTS .
Pp
Fa tptrp
is a pointer to a pointer to an 8-bit byte and
Fa *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,
Fa *tptrp
must be set to
Dv NULL .
Pa
This function starts searching for an option of the specified type
beginning after the value of
Fa *tptrp .
If an option of the specified
type is located, this function returns
Li 0
and
Fa *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
Li -1
and
Fa *tptrp
is
Dv NULL .
If an error occurs, the return value is
Li -1
and
Fa *tptrp
is not
Dv NULL .
\"
Sh EXAMPLES
RFC 2292 gives comprehensive examples in chapter 6.
\"
Sh RETURN VALUES
Fn inet6_option_init
and
Fn inet6_option_append
return
Li 0
on success or
Li -1
on an error.
Pp
Fn inet6_option_alloc
returns
Dv NULL
on an error.
Pp
On errors,
Fn inet6_option_next
and
Fn inet6_option_find
return
Li -1
setting
Fa *tptrp
to non
Dv NULL
value.
\"
Sh SEE ALSO
Rs
%A W. Stevens
%A M. Thomas
%T "Advanced Sockets API for IPv6"
%N RFC 2292
%D February 1998
Re
Rs
%A S. Deering
%A R. Hinden
%T "Internet Protocol, Version 6 (IPv6) Specification"
%N RFC 2460
%D December 1998
Re
\"
Sh STANDARDS
The functions
are documented in
Dq Advanced Sockets API for IPv6
Pq RFC 2292 .
\"
Sh HISTORY
The implementation first appeared in KAME advanced networking kit.
\"
Sh BUGS
The text was shamelessly copied from RFC 2292.

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