.\"	$OpenBSD: inet6_rthdr_space.3,v 1.13 2003/08/08 09:26:02 jmc Exp $
.\"	$KAME: inet6_rthdr_space.3,v 1.8 2000/05/17 14:30:15 itojun Exp $
.\"
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.Dd December 10, 1999
.Dt INET6_RTHDR_SPACE 3
.Os
.\"
.Sh NAME
.Nm inet6_rthdr_space ,
.Nm inet6_rthdr_init ,
.Nm inet6_rthdr_add ,
.Nm inet6_rthdr_lasthop ,
.Nm inet6_rthdr_reverse ,
.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
RFC 2292 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 Pa 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 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
(which must have a value between 1 and the value returned by
.Fn inet6_rthdr_segments )
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
(which must
have a value between 0 and the value returned by
.Fn inet6_rthdr_segments )
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 RFC 2460.
.\"
.Sh EXAMPLES
RFC 2292 gives comprehensive examples in chapter 8.
.\"
.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 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.
.Pp
.Fn inet6_rthdr_reverse
is not implemented yet.