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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
     kernel 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
     networking 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
     structures for a route corresponding to a particular end-node address,
     and to cause certain protocol- and interface-specific actions to take

     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
     database (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
     structure 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
     reference 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
     require 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
     default 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
     success 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
     different internals.  The rtalloc_ign() function and the flags argument
     to rtalloc1() first appeared in FreeBSD 2.0.  Routing table locking was
     introduced 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 11.0-PRERELEASE          July 4, 2012          FreeBSD 11.0-PRERELEASE


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