.\"	$KAME: kame/kame/kame/libinet6/inet6_rth_space.3,v 1.4 2002/10/17 14:13:48 jinmei Exp $
.\"
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.\" $FreeBSD$
.\"
.Dd February 5, 2000
.Dt INET6_RTH_SPACE 3
.Os
.\"
.Sh NAME
.Nm inet6_rth_space
.Nm inet6_rth_init
.Nm inet6_rth_add
.Nm inet6_rth_reverse
.Nm inet6_rth_segments
.Nm inet6_rth_getaddr
.Nd IPv6 Routing Header Options manipulation
.\"
.Sh SYNOPSIS
.In netinet/in.h
.Ft socklen_t
.Fn inet6_rth_space "int" "int"
.Ft "void *"
.Fn inet6_rth_init "void *" "socklen_t" "int" "int"
.Ft int
.Fn inet6_rth_add "void *" "const struct in6_addr *"
.Ft int
.Fn inet6_rth_reverse "const void *" "void *"
.Ft int
.Fn inet6_rth_segments "const void *"
.Ft "struct in6_addr *"
.Fn inet6_rth_getaddr "const void *" "int"
.\"
.Sh DESCRIPTION
The IPv6 advanced API defines six
functions that the application calls to build and examine a Routing
header, and the ability to use sticky options or ancillary data to
communicate this information between the application and the kernel
using the IPV6_RTHDR option.
.Pp
Three functions build a Routing header:
.Bl -hang
.It Fn inet6_rth_space
returns #bytes required for Routing header
.It Fn inet6_rth_init
initializes buffer data for Routing header
.It Fn inet6_rth_add
adds one IPv6 address to the Routing header
.El
.Pp
Three functions deal with a returned Routing header:
.Bl -hang
.It Fn inet6_rth_reverse
reverses a Routing header
.It Fn inet6_rth_segments
returns #segments in a Routing header
.It Fn inet6_rth_getaddr
fetches one address from a Routing header
.El
.Pp
The function prototypes for these functions are defined as a result
of including the
.Aq Li netinet/in.h
header.
.\"
.Ss inet6_rth_space
.Fn inet6_rth_space
returns the number of bytes required to hold a Routing
header of the specified type containing the specified number of
.Li segments
.Po addresses.
.Pc
For an IPv6 Type 0 Routing header, the number
of
.Li segments
must be between 0 and 127, inclusive.
The return value is just the space for the Routing header.
When the application uses
ancillary data it must pass the returned length to
.Fn CMSG_LEN
to determine how much memory is needed for the ancillary data object
.Po
including the cmsghdr structure.
.Pc
.Pp
If the return value is 0, then either the type of the Routing header
is not supported by this implementation or the number of segments is
invalid for this type of Routing header.
.Pp
Note: This function returns the size but does not allocate the space
required for the ancillary data.
This allows an application to
allocate a larger buffer, if other ancillary data objects are
desired, since all the ancillary data objects must be specified to
.Fn sendmsg
as a single msg_control buffer.
.Ss inet6_rth_init
.Fn inet6_rth_init
initializes the buffer pointed to by
.Li bp
to contain a
Routing header of the specified type and sets ip6r_len based on the
.Li segments
parameter.
.Li bp_len
is only used to verify that the buffer is
large enough.
The ip6r_segleft field is set to zero;
.Fn inet6_rth_add
will increment it.
.Pp
When the application uses ancillary data the application must
initialize any cmsghdr fields.
.Pp
The caller must allocate the buffer and its size can be determined by
calling
.Fn inet6_rth_space .
.Pp
Upon success the return value is the pointer to the buffer
.Li bp ,
and this is then used as the first argument to the next two functions.
Upon an error the return value is NULL.
.\"
.Ss inet6_rth_add
.Fn inet6_rth_add
adds the IPv6 address pointed to by
.Li addr
to the end of the Routing header being constructed.
.Pp
If successful, the segleft member of the Routing Header is updated to
account for the new address in the Routing header and the return
value of the function is 0.
Upon an error the return value of the function is -1.
.\"
.Ss inet6_rth_reverse
.Fn inet6_rth_reverse
takes a Routing header extension header
.Po
pointed to by the first argument
.Li in
.Pc
and writes a new Routing header that sends
datagrams along the reverse of that route.
Both arguments are allowed to point to the same buffer
.Po
that is, the reversal can occur in place.
.Pc
.Pp
The return value of the function is 0 on success, or -1 upon an error.
.\"
.Ss inet6_rth_segments
.Fn inet6_rth_segments
returns the number of segments
.Po
addresses
.Pc
contained in the Routing header described by
.Li bp .
On success the return value is
zero or greater.
The return value of the function is -1 upon an error.
.\"
.Ss inet6_rth_getaddr
.Fn inet6_rth_getaddr
returns a pointer to the IPv6 address specified by
.Li index
.Po
which must have a value between 0 and one less than the value
returned by
.Fn inet6_rth_segments
.Pc
in the Routing header described by
.Li bp .
An application should first call
.Fn inet6_rth_segments
to obtain the number of segments in the Routing header.
.Pp
Upon an error the return value of the function is NULL.
.\"
.Sh DIAGNOSTICS
.Fn inet6_rth_space
and
.FN inet6_rth_getaddr
return 0 on errors.
.Pp
.Fn inet6_rthdr_init
returns
.Dv NULL
on error.
.Fn inet6_rth_add
and
.Fn inet6_rth_reverse
return0 on success, or -1 upon an error.
.\"
.Sh EXAMPLES
draft-ietf-ipngwg-rfc2292bis-08.txt
gives comprehensive examples in Section 22.
.Pp
KAME also provides examples in the advapitest directry of its kit.
.\"
.Sh SEE ALSO
.Rs
.%A W. Stevens
.%A M. Thomas
.%A E. Nordmark
.%A E. Jinmei
.%T "Advanced Sockets API for IPv6"
.%N draft-ietf-ipngwg-rfc2292bis-08
.%D October 2002
.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 draft-ietf-ipngwg-rfc2292bis-08.txt .
.\"
.Sh BUGS
The text was shamelessly copied from internet-drafts for RFC2292bis.