202 lines
5.6 KiB
Groff
202 lines
5.6 KiB
Groff
.\"
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.\" Copyright 1996 Massachusetts Institute of Technology
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.\"
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.\" Permission to use, copy, modify, and distribute this software and
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.\" its documentation for any purpose and without fee is hereby
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.\" granted, provided that both the above copyright notice and this
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.\" permission notice appear in all copies, that both the above
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.\" copyright notice and this permission notice appear in all
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.\" supporting documentation, and that the name of M.I.T. not be used
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.\" in advertising or publicity pertaining to distribution of the
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.\" software without specific, written prior permission. M.I.T. makes
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.\" no representations about the suitability of this software for any
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.\" purpose. It is provided "as is" without express or implied
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.\" warranty.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
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.\" ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
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.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
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.\" SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $Id: rtalloc.9,v 1.1 1996/10/08 18:45:06 wollman Exp $
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.Dd October 8, 1996
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.Os
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.Dt RTALLOC 9
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.Sh NAME
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.Nm rtalloc ,
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.Nm rtalloc_ign ,
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.Nm rtalloc1
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.Nd look up a route in the kernel routing table
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.Sh SYNOPSIS
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.Fd #include <sys/socket.h>
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.Fd #include <net/route.h>
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.Ft void
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.Fn rtalloc "struct route *ro"
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.Ft void
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.Fn rtalloc_ign "struct route *ro" "u_long flags"
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.Ft "struct rtentry *"
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.Fn rtalloc1 "struct sockaddr *sa" "int report" "u_long flags"
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.Sh DESCRIPTION
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The kernel uses a radix tree structure to manage routes for the
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networking subsystem. The
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.Fn rtalloc
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family of routines is used by protocols to query this structure for a
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route corresponding to a particular end-node address, and to cause
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certain protocol\- and interface-specific actions to take place.
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.\" XXX - -mdoc should contain a standard request for getting em and
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\" en dashes.
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.Pp
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When a route with the flag
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.Dv RTF_CLONING
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or
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.Dv RTF_PRCLONING
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is retrieved, and the action of those flags is not masked, the
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.Nm rtalloc
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facility automatically generates a new route using information in the
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old route as a template, and in the case of
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.Dv RTF_CLONING ,
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sends an
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.Dv RTM_RESOLVE
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message to the appropriate interface-address route-management routine
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.Pq Fn ifa->ifa_rtrequest .
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.Dv RTF_PRCLONING
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routes are assumed to be managed by the protcol family and no
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resolution requests are made, but all routes generated by the cloning
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process retain a reference to the route from which they were
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generated.
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If the
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.Dv RTF_XRESOLVE
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flag is set, then the
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.Dv RTM_RESOLVE
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message is sent instead on the
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.Xr route 4
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socket interface, requesting that an external program resolve the
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address in question and modify the route appropriately.
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.Pp
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The default interface is
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.Fn rtalloc .
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Its only argument is
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.Ar ro ,
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a pointer to a
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.Dq Li "struct route" ,
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which is defined as follows:
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.Bd -literal -offset indent
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struct route {
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struct sockaddr ro_dst;
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struct rtentry *ro_rt;
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};
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.Ed
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Thus, this function can only be used for address families which are
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smaller than the default
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.Dq Li "struct sockaddr" .
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Before calling
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.Fn rtalloc
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for the first time, callers should ensure that unused bits of the
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structure are set to zero. On subsequent calls,
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.Fn rtalloc
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returns without performing a lookup if
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.Ar ro->ro_rt
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is non-null and the
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.Dv RTF_UP
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flag is set in the route's
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.Li rt_flags
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field.
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.Pp
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The
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.Fn rtalloc_ign
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interface can be used when the default actions of
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.Fn rtalloc
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in the presence of the
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.Dv RTF_CLONING
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and
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.Dv RTF_PRCLONING
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flags are undesired. The
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.Ar ro
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argument is the same as
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.Fn rtalloc ,
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but there is additionally a
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.Ar flags
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argument, which lists the flags in the route which are to be
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.Em ignored
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(ordinarily, one or both of
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.Dv RTF_CLONING
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or
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.Dv RTF_PRCLONING ) .
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.Pp
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The
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.Fn rtalloc1
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function is the most general form of
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.Fn rtalloc
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(and both of the other forms are implemented as calls to rtalloc1).
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It does not use the
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.Dq Li "struct route" ,
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and is therefore suitable for address families which require more
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space than is in a traditional
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.Dq Li "struct sockaddr" .
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Instead, it takes a
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.Dq Li "struct sockaddr *"
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directly as the
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.Ar sa
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argument. The second argument,
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.Ar report ,
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controls whether
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.Dv RTM_RESOLVE
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requests are sent to the lower layers when an
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.Dv RTF_CLONING
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or
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.Dv RTF_PRCLONING
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route is cloned. Ordinarily a value of one should be passed, except
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in the processing of those lower layers which use the cloning
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facility.
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The third argument,
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.Ar flags ,
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is a set of flags to ignore, as in
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.Fn rtalloc_ign .
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.Sh RETURN VALUES
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The
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.Fn rtalloc
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and
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.Fn rtalloc_ign
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functions do not return a value. The
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.Fn rtalloc1
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function returns a pointer to a routing-table entry if it succeeds,
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otherwise a null pointer. Lack of a route should in most cases be
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translated to the
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.Xr errno 2
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value
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.Er EHOSTUNREACH .
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.Sh SEE ALSO
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.Xr route 4 ,
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.Xr rtentry 9
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.Sh HISTORY
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The
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.Nm rtalloc
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facility first appeared in
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.Bx 4.2 ,
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although with much different internals. The
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.Fn rtalloc_ign
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function and the
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.Ar flags
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argument to
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.Fn rtalloc1
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first appeared in
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.Fx 2.0 .
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.Sh AUTHOR
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This manual page was written by Garrett Wollman, as were the changes
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to implement
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.Dv RTF_PRCLONING
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and the
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.Fn rtalloc_ign
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function and the
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.Ar flags
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argument to
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.Fn rtalloc1 .
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