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.\"     $OpenBSD: inet6_option_space.3,v 1.8 2001/06/23 05:57:04 deraadt Exp $

.\"     $KAME: inet6_option_space.3,v 1.7 2000/05/17 14:32:13 itojun Exp $

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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

.Fd #include 

.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 u_int8_t *typep" "int multx" "int plusy"

.Ft "u_int8_t *"

.Fn inet6_option_alloc "struct cmsghdr *cmsg" "int datalen" "int multx" "int plusy";

.Ft "int"

.Fn inet6_option_next "const struct cmsghdr *cmsg" "u_int8_t **tptrp"

.Ft "int"

.Fn inet6_option_find "const struct cmsghdr *cmsg" "u_int8_t **tptrp" "int type"

.\"

.Sh DESCRIPTION

.\"

Building and parsing the Hop-by-Hop and Destination options is

complicated due to alignment constranints, 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

.Aq Li 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 DIAGNOSTICS

.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 EXAMPLES

RFC2292 gives comprehensive examples in chapter 6.

.\"

.Sh SEE ALSO

.Rs

.%A W. Stevens

.%A M. Thomas

.%T "Advanced Sockets API for IPv6"

.%N RFC2292

.%D February 1998

.Re

.Rs

.%A S. Deering

.%A R. Hinden

.%T "Internet Protocol, Version 6 (IPv6) Specification"

.%N RFC2460

.%D December 1998

.Re

.\"

.Sh HISTORY

The implementation first appeared in KAME advanced networking kit.

.\"

.Sh STANDARDS

The functions

are documented in

.Dq Advanced Sockets API for IPv6

.Pq RFC2292 .

.\"

.Sh BUGS

The text was shamelessly copied from RFC2292.