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.\" $FreeBSD: src/share/man/man9/rtalloc.9,v 1.20.2.2.2.1 2010/12/21 17:09:25 kensmith Exp $
.\"
.Dd December 11, 2008
.Dt RTALLOC 9
.Os
.Sh NAME
.Nm rtalloc ,
.Nm rtalloc_ign ,
.Nm rtalloc1 ,
.Nm rtfree
.Nd look up a route in the kernel routing table
.Sh SYNOPSIS
.In sys/types.h
.In sys/socket.h
.In net/route.h
.Ft void
.Fn rtalloc "struct route *ro"
.Ft void
.Fn rtalloc_ign "struct route *ro" "u_long flags"
.Ft "struct rtentry *"
.Fn rtalloc1 "struct sockaddr *sa" "int report" "u_long flags"
.Ft void
.Fn rtfree "struct rt_entry *rt"
.Fn RTFREE "struct rt_entry *rt"
.Fn RT_LOCK "struct rt_entry *rt"
.Fn RT_UNLOCK "struct rt_entry *rt"
.Fn RT_ADDREF "struct rt_entry *rt"
.Fn RT_REMREF "struct rt_entry *rt"
.Sh DESCRIPTION
The kernel uses a radix tree structure to manage routes for the
networking subsystem.
The
.Fn rtalloc
family of routines is used by protocols to query this structure for a
route corresponding to a particular end-node address, and to cause
certain protocol\- and interface-specific actions to take place.
.\" XXX - -mdoc should contain a standard request for getting em and
.\" en dashes.
.Pp
.Dv RTF_PRCLONING
flag is obsolete and thus ignored by facility.
If the
.Dv RTF_XRESOLVE
flag is set, then the
.Dv RTM_RESOLVE
message is sent instead on the
.Xr route 4
socket interface, requesting that an external program resolve the
address in question and modify the route appropriately.
.Pp
The default interface is
.Fn rtalloc .
Its only argument is
.Fa ro ,
a pointer to a
.Dq Li "struct route" ,
which is defined as follows:
.Bd -literal -offset indent
struct route {
	struct sockaddr ro_dst;
	struct rtentry *ro_rt;
};
.Ed
.Pp
Thus, this function can only be used for address families which are
smaller than the default
.Dq Li "struct sockaddr" .
Before calling
.Fn rtalloc
for the first time, callers should ensure that unused bits of the
structure are set to zero.
On subsequent calls,
.Fn rtalloc
returns without performing a lookup if
.Fa ro->ro_rt
is non-null and the
.Dv RTF_UP
flag is set in the route's
.Li rt_flags
field.
.Pp
The
.Fn rtalloc_ign
interface can be used when the caller does not want to receive
the returned
.Fa rtentry
locked.
The
.Fa ro
argument is the same as
.Fn rtalloc ,
but there is additionally a
.Fa flags
argument, which is now only used to pass
.Dv RTF_RNH_LOCKED
indicating that the radix tree lock is already held.
Both
.Fn rtalloc
and
.Fn rtalloc_ign
functions return a pointer to an unlocked
.Vt "struct rtentry" .
.Pp
The
.Fn rtalloc1
function is the most general form of
.Fn rtalloc
(and both of the other forms are implemented as calls to rtalloc1).
It does not use the
.Dq Li "struct route" ,
and is therefore suitable for address families which require more
space than is in a traditional
.Dq Li "struct sockaddr" .
Instead, it takes a
.Dq Li "struct sockaddr *"
directly as the
.Fa sa
argument.
The second argument,
.Fa report ,
controls whether the lower layers are notified when a lookup fails.
The third argument,
.Fa flags ,
is a set of flags to ignore, as in
.Fn rtalloc_ign .
The
.Fn rtalloc1
function returns a pointer to a locked
.Vt "struct rtentry" .
.Pp
The
.Fn rtfree
function frees a locked route entry, e.g., a previously allocated by
.Fn rtalloc1 .
.Pp
The
.Fn RTFREE
macro is used to free unlocked route entries, previously allocated by
.Fn rtalloc
or
.Fn rtalloc_ign .
The
.Fn RTFREE
macro decrements the reference count on the routing table entry (see below),
and frees it if the reference count has reached zero.
.Pp
The preferred usage is allocating a route using
.Fn rtalloc
or
.Fn rtalloc_ign
and freeing using
.Fn RTFREE .
.Pp
The
.Fn RT_LOCK
macro is used to lock a routing table entry.
The
.Fn RT_UNLOCK
macro is used to unlock a routing table entry.
.Pp
The
.Fn RT_ADDREF
macro increments the reference count on a previously locked route entry.
The
.Fn RT_REMREF
macro decrements the reference count on a previously locked route entry.
.Sh RETURN VALUES
The
.Fn rtalloc ,
.Fn rtalloc_ign
and
.Fn rtfree
functions do not return a value.
The
.Fn rtalloc1
function returns a pointer to a routing-table entry if it succeeds,
otherwise a null pointer.
Lack of a route should in most cases be
translated to the
.Xr errno 2
value
.Er EHOSTUNREACH .
.Sh SEE ALSO
.Xr route 4 ,
.Xr rtentry 9
.Sh HISTORY
The
.Nm
facility first appeared in
.Bx 4.2 ,
although with much different internals.
The
.Fn rtalloc_ign
function and the
.Fa flags
argument to
.Fn rtalloc1
first appeared in
.Fx 2.0 .
Routing table locking was introduced in
.Fx 5.2 .
.Sh AUTHORS
This manual page was written by
.An Garrett Wollman ,
as were the changes to implement
.Dv RTF_PRCLONING
and the
.Fn rtalloc_ign
function and the
.Fa flags
argument to
.Fn rtalloc1 .