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

     rtalloc1_fib, rtalloc_ign_fib, rtalloc_fib	-- look	up a route in the ker-
     nel routing table

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

     struct rtentry *
     rtalloc1_fib(struct sockaddr *dst,	int report, u_long flags,
	 u_int fibnum);

     rtalloc_fib(struct	route *ro, u_int fibnum);

     rtalloc_ign_fib(struct route *ro, u_long flags, u_int fibnum);

     RTFREE_LOCKED(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);

     RO_RTFREE(struct route *ro);

     rtfree(struct rt_entry *rt);

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

     rtalloc(struct route *ro);

     rtalloc_ign(struct	route *ro, u_long flags);

     options RADIX_MPATH

     The kernel	uses a radix tree structure to manage routes for the network-
     ing subsystem.  If	compiled with options RADIX_MPATH kernel may maintain
     several independent forwarding information	databases (FIBs).  The
     rtalloc() family of routines is used by protocols to query	these struc-
     tures for a route corresponding to	a particular end-node address, and to
     cause certain protocol- and interface-specific actions to take place.

     The rtalloc1_fib()	function is the	most general form of rtalloc(),	and
     all of the	other forms are	implemented as calls to	it.  It	takes a	struct
     sockaddr *	directly as the	dst argument.  The second argument, report,
     controls whether the routing sockets are notified when a lookup fails.
     The third argument, flags,	is a combination of the	following values:

	   RTF_RNH_LOCKED indicates that the radix tree	lock is	already	held

     The last argument fibnum specifies	number of forwarding information data-
     base (FIB)	on which the lookup should be performed.  In case of success
     the rtalloc1_fib()	function returns a pointer to a	locked struct rtentry
     with an additional	reference.

     The rtalloc_fib() is the most simple variant.  Its	main argument is ro, a
     pointer to	a struct route,	which is defined as follows:

	   struct route	{
		   struct rtentry *ro_rt;
		   struct llentry *ro_lle;
		   struct sockaddr ro_dst;

     Thus, this	function can only be used for address families which are
     smaller than the default struct sockaddr.	Before calling rtalloc_fib()
     for the first time, callers should	ensure that unused bits	of the struc-
     ture are set to zero.  The	second argument	fibnum is FIB number.  In case
     of	success	of the rtalloc_fib() the ro_rt points to a valid and unlocked
     rtentry(9), which has an additional reference put on it, freeing which is
     responsibility of the caller.  On subsequent calls, rtalloc_fib() returns
     without performing	a lookup if ro-_ro_rt is non-null and the RTF_UP flag
     is	set in the rtentry's rt_flags field.

     The rtalloc_ign_fib() function is the same	as the rtalloc_fib(), but
     there is additional flags argument, which is same as in rtalloc1_fib().

     The RTFREE_LOCKED() macro is used to unref	and possibly free a locked
     routing entry with	one our	reference, for example previously allocated by

     The RTFREE() macro	is used	to unref and possibly free an unlocked route
     entries with one our reference, for example previously allocated by
     rtalloc_fib() or rtalloc_ign_fib().

     Both RTFREE_LOCKED() and RTFREE() macros decrement	the reference count on
     the routing table entry, and proceed with actual freeing if the reference
     count has reached zero.

     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.  It should be used whenever a reference to an
     rtentry(9)	is going to be stored outside the routing table.

     The RT_REMREF() macro decrements the reference count on a previously
     locked route entry.  Its usage is contrary	to RT_ADDREF().

     The RO_RTFREE() macro is used to free route entry that is referenced by
     struct route.  At certain circumstances the latter	may not	hold a refer-
     ence on rtentry, and RO_RTFREE() treats such routes correctly.

     The rtfree() function does	the actual free	of the routing table entry,
     and shouldn't be called directly by facilities, that just perform routing
     table lookups.

     Prior to introduction of multiple routing tables functions	did not	re-
     quire the u_int fibnum argument.  Legacy rtalloc1(), rtalloc() and
     rtalloc_ign() functions are kept for compatibility, and are equivalent to
     calling new interface with	fibnum argument	equal to 0, which implies de-
     fault forwarding table.

     The rtalloc1_fib()	function returns a pointer to a	locked routing-table
     entry if it succeeds, otherwise a null pointer.  The rtalloc_fib()	and
     rtalloc_ign_fib() functions do not	return a value,	but they fill in the
     *ro_rt member of the *ro argument with a pointer to an unlocked routing-
     table entry if they succeed, otherwise a null pointer.  In	a case of suc-
     cess all functions	put a reference	on the routing-table entry, freeing of
     which is responsibility of	the caller.  Lack of a route should in most
     cases be translated to the	errno(2) value EHOSTUNREACH.

     route(4), rtentry(9)

     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.  Multiple	routing	tables were introduced in
     FreeBSD 8.0.

     The original version of this manual page was written by Garrett Wollman.
     It	was significantly updated by Gleb Smirnoff.

FreeBSD	13.0			 July 4, 2012			  FreeBSD 13.0


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