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RTALLOC(9)		 BSD Kernel Developer's	Manual		    RTALLOC(9)

NAME
     rtalloc, rtalloc_ign, rtalloc1, rtfree -- look up a route in the kernel
     routing table

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <net/route.h>

     void
     rtalloc(struct route *ro);

     void
     rtalloc_ign(struct	route *ro, u_long flags);

     struct rtentry *
     rtalloc1(struct sockaddr *sa, int report, u_long flags);

     void
     rtfree(struct rt_entry *rt);

     RTFREE(struct rt_entry *rt);

     RT_LOCK(struct rt_entry *rt);

     RT_UNLOCK(struct rt_entry *rt);

     RT_ADDREF(struct rt_entry *rt);

     RT_REMREF(struct rt_entry *rt);

DESCRIPTION
     The kernel	uses a radix tree structure to manage routes for the network-
     ing subsystem.  The 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.

     When a route with the flag	RTF_CLONING is retrieved, and the action of
     this flag is not masked, the rtalloc facility automatically generates a
     new route using information in the	old route as a template, and sends an
     RTM_RESOLVE message to the	appropriate interface-address route-management
     routine (ifa->ifa_rtrequest()).  This generated route is called cloned,
     and has RTF_WASCLONED flag	set.  RTF_PRCLONING flag is obsolete and thus
     ignored by	facility.  If the RTF_XRESOLVE flag is set, then the
     RTM_RESOLVE message is sent instead on the	route(4) socket	interface, re-
     questing that an external program resolve the address in question and
     modify the	route appropriately.

     The default interface is rtalloc().  Its only argument is ro, a pointer
     to	a "struct route", which	is defined as follows:

	   struct route	{
		   struct sockaddr ro_dst;
		   struct rtentry *ro_rt;
	   };

     Thus, this	function can only be used for address families which are
     smaller than the default "struct sockaddr".  Before calling rtalloc() for
     the first time, callers should ensure that	unused bits of the structure
     are set to	zero.  On subsequent calls, rtalloc() returns without perform-
     ing a lookup if ro-_ro_rt is non-null and the RTF_UP flag is set in the
     route's rt_flags field.

     The rtalloc_ign() interface can be	used when the default actions of
     rtalloc() in the presence of the RTF_CLONING flag is undesired.  The ro
     argument is the same as rtalloc(),	but there is additionally a flags ar-
     gument, which lists the flags in the route	which are to be	ignored	(in
     most cases	this is	RTF_CLONING flag).  Both rtalloc() and rtalloc_ign()
     functions return a	pointer	to an unlocked struct rtentry.

     The rtalloc1() function is	the most general form of rtalloc() (and	both
     of	the other forms	are implemented	as calls to rtalloc1).	It does	not
     use the "struct route", and is therefore suitable for address families
     which require more	space than is in a traditional "struct sockaddr".  In-
     stead, it takes a "struct sockaddr	*" directly as the sa argument.	 The
     second argument, report, controls whether RTM_RESOLVE requests are	sent
     to	the lower layers when an RTF_CLONING or	RTF_PRCLONING route is cloned.
     Ordinarily	a value	of one should be passed, except	in the processing of
     those lower layers	which use the cloning facility.	 The third argument,
     flags, is a set of	flags to ignore, as in rtalloc_ign().  The rtalloc1()
     function returns a	pointer	to a locked struct rtentry.

     The rtfree() function frees a locked route	entry, e.g., a previously al-
     located by	rtalloc1().

     The RTFREE() macro	is used	to free	unlocked route entries,	previously al-
     located by	rtalloc() or rtalloc_ign().  The RTFREE() macro	decrements the
     reference count on	the routing table entry	(see below), and frees it if
     the reference count has reached zero.

     The preferred usage is allocating a route using rtalloc() or
     rtalloc_ign() and freeing using RTFREE().

     The RT_LOCK() macro is used to lock a routing table entry.	 The
     RT_UNLOCK() macro is used to unlock a routing table entry.

     The RT_ADDREF() macro increments the reference count on a previously
     locked route entry.  The RT_REMREF() macro	decrements the reference count
     on	a previously locked route entry.

RETURN VALUES
     The rtalloc(), rtalloc_ign() and rtfree() functions do not	return a
     value.  The rtalloc1() function returns a pointer to a routing-table en-
     try if it succeeds, otherwise a null pointer.  Lack of a route should in
     most cases	be translated to the errno(2) value EHOSTUNREACH.

SEE ALSO
     route(4), rtentry(9)

HISTORY
     The rtalloc facility first	appeared in 4.2BSD, although with much differ-
     ent internals.  The rtalloc_ign() function	and the	flags argument to
     rtalloc1()	first appeared in FreeBSD 2.0.	Routing	table locking was in-
     troduced in FreeBSD 5.2.

AUTHORS
     This manual page was written by Garrett Wollman, as were the changes to
     implement RTF_PRCLONING and the rtalloc_ign() function and	the flags ar-
     gument to rtalloc1().

BSD			       October 11, 2004				   BSD

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | SEE ALSO | HISTORY | AUTHORS

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