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+.\" Copyright (c) 1983, 1987, 1991, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     $Id: inet6_rthdr_space.3,v 1.5 2000/02/05 13:19:07 jinmei Exp $
+.\" $FreeBSD$
+.\"
+.Dd December 10, 1999
+.Dt INET6_OPTION_SPACE 3
+.Os KAME
+.\"
+.Sh NAME
+.Nm inet6_rthdr_space ,
+.Nm inet6_rthdr_init ,
+.Nm inet6_rthdr_add ,
+.Nm inet6_rthdr_lasthop ,
+.Nm inet6_rthdr_reversoe ,
+.Nm inet6_rthdr_segments ,
+.Nm inet6_rthdr_getaddr ,
+.Nm inet6_rthdr_getflags
+.Nd IPv6 Routing Header Options manipulation
+.\"
+.Sh SYNOPSIS
+.Fd #include <netinet/in.h>
+.Ft size_t
+.Fn inet6_rthdr_space "int type" "int segments"
+.Ft "struct cmsghdr *"
+.Fn inet6_rthdr_init "void *bp" "int type"
+.Ft int
+.Fn inet6_rthdr_add "struct cmsghdr *cmsg" "const struct in6_addr *addr" "unsigned int flags"
+.Ft int
+.Fn inet6_rthdr_lasthop "struct cmsghdr *cmsg" "unsigned int flags"
+.Ft int
+.Fn inet6_rthdr_reverse "const struct cmsghdr *in" "struct cmsghdr *out"
+.Ft int
+.Fn inet6_rthdr_segments "const struct cmsghdr *cmsg"
+.Ft "struct in6_addr *"
+.Fn inet6_rthdr_getaddr "struct cmsghdr *cmsg" "int index"
+.Ft int
+.Fn inet6_rthdr_getflags "const struct cmsghdr *cmsg" "int index"
+.\"
+.Sh DESCRIPTION
+RFC2292 IPv6 advanced API defines eight
+functions that the application calls to build and examine a Routing
+header.  Four functions build a Routing header:
+.Bl -hang
+.It Fn inet6_rthdr_space
+return #bytes required for ancillary data
+.It Fn inet6_rthdr_init
+initialize ancillary data for Routing header
+.It Fn inet6_rthdr_add
+add IPv6 address & flags to Routing header
+.It Fn inet6_rthdr_lasthop
+specify the flags for the final hop
+.El
+.Pp
+Four functions deal with a returned Routing header:
+.Bl -hang
+.It Fn inet6_rthdr_reverse
+reverse a Routing header
+.It Fn inet6_rthdr_segments
+return #segments in a Routing header
+.It Fn inet6_rthdr_getaddr
+fetch one address from a Routing header
+.It Fn inet6_rthdr_getflags
+fetch one flag from a Routing header
+.El
+.Pp
+The function prototypes for these functions are all in the
+.Aq Li netinet/in.h
+header.
+.\"
+.Ss inet6_rthdr_space
+This function returns the number of bytes required to hold a Routing
+header of the specified
+.Fa type
+containing the specified number of
+.Fa segments
+.Pq addresses .
+For an IPv6 Type 0 Routing header, the number
+of segments must be between 1 and 23, inclusive.  The return value
+includes the size of the cmsghdr structure that precedes the Routing
+header, and any required padding.
+.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
+.Xr sendmsg 2
+as a single
+.Li msg_control
+buffer.
+.\"
+.Ss inet6_rthdr_init
+This function initializes the buffer pointed to by
+.Fa bp
+to contain a
+.Li cmsghdr
+structure followed by a Routing header of the specified
+.Fa type .
+The
+.Li cmsg_len
+member of the
+.Li cmsghdr
+structure is initialized to the
+size of the structure plus the amount of space required by the
+Routing header.
+The
+.Li cmsg_level
+and
+.Li cmsg_type
+members are also initialized as required.
+.Pp
+The caller must allocate the buffer and its size can be determined by
+calling
+.Fn inet6_rthdr_space .
+.Pp
+Upon success the return value is the pointer to the
+.Li cmsghdr
+structure, and this is then used as the first argument to the next
+two functions.
+Upon an error the return value is
+.Dv NULL .
+.\"
+.Ss inet6_rthdr_add
+This function adds the address pointed to by
+.Fa addr
+to the end of the
+Routing header being constructed and sets the type of this hop to the
+value of
+.Fa flags .
+For an IPv6 Type 0 Routing header,
+.Fa flags
+must be
+either
+.Dv IPV6_RTHDR_LOOSE
+or
+.Dv IPV6_RTHDR_STRICT .
+.Pp
+If successful, the
+.Li cmsg_len
+member of the
+.Li cmsghdr
+structure 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_rthdr_lasthop
+This function specifies the Strict/Loose flag for the final hop of a
+Routing header.
+For an IPv6 Type 0 Routing header,
+.Fa flags
+must be either
+.Dv IPV6_RTHDR_LOOSE
+or
+.Dv IPV6_RTHDR_STRICT .
+.Pp
+The return value of the function is 0 upon success, or -1 upon an error.
+.Pp
+Notice that a Routing header specifying
+.Li N
+intermediate nodes requires
+.Li N+1
+Strict/Loose flags.
+This requires
+.Li N
+calls to
+.Fn inet6_rthdr_add
+followed by one call to
+.Fn inet6_rthdr_lasthop .
+.\"
+.Ss inet6_rthdr_reverse
+This function is not yet implemented.
+When implemented, this should behave as follows.
+.Pp
+This function takes a Routing header that was received as ancillary
+data
+.Po
+pointed to by the first argument,
+.Fa 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
+.Pq that is, the reversal can occur in place .
+.Pp
+The return value of the function is 0 on success, or -1 upon an
+error.
+.\"
+.Ss inet6_rthdr_segments
+This function returns the number of segments
+.Pq addresses
+contained in
+the Routing header described by
+.Fa cmsg .
+On success the return value is
+between 1 and 23, inclusive.
+The return value of the function is -1 upon an error.
+.\"
+.Ss inet6_rthdr_getaddr
+This function returns a pointer to the IPv6 address specified by
+.Fa index
+.Po
+which must have a value between 1 and the value returned by
+.Fn inet6_rthdr_segments
+.Pc
+in the Routing header described by
+.Fa cmsg .
+An
+application should first call
+.Fn inet6_rthdr_segments
+to obtain the number of segments in the Routing header.
+.Pp
+Upon an error the return value of the function is
+.Dv NULL .
+.\"
+.Ss inet6_rthdr_getflags
+This function returns the flags value specified by
+.Fa index
+.Po
+which must
+have a value between 0 and the value returned by
+.Fn inet6_rthdr_segments
+.Pc
+in the Routing header described by
+.Fa cmsg .
+For an IPv6 Type 0 Routing header the return value will be either
+.Dv IPV6_RTHDR_LOOSE
+or
+.Dv IPV6_RTHDR_STRICT .
+.Pp
+Upon an error the return value of the function is -1.
+.Pp
+Note: Addresses are indexed starting at 1, and flags starting at 0,
+to maintain consistency with the terminology and figures in RFC2460.
+.\"
+.Sh DIAGNOSTICS
+.Fn inet6_rthdr_space
+returns 0 on errors.
+.Pp
+.Fn inet6_rthdr_add ,
+.Fn inet6_rthdr_lasthop
+and
+.Fn inet6_rthdr_reverse
+return 0 on success, and returns -1 on error.
+.Pp
+.Fn inet6_rthdr_init
+and
+.Fn inet6_rthdr_getaddr
+return
+.Dv NULL
+on error.
+.Pp
+.Fn inet6_rthdr_segments
+and
+.Fn inet6_rthdr_getflags
+return -1 on error.
+.\"
+.Sh EXAMPLES
+RFC2292 gives comprehensive examples in chapter 8.
+.\"
+.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.
+.Pp
+.Fn inet6_rthdr_reverse
+is not implemented yet.