RTALLOC(9) BSD Kernel Developer's Manual RTALLOC(9)
NAME
rtalloc1_fib, rtalloc_ign_fib, rtalloc_fib -- look up a route in the kernel routing table
SYNOPSIS
#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);
void
rtalloc_fib(struct route *ro, u_int fibnum);
void
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);
void
rtfree(struct rt_entry *rt);
struct rtentry *
rtalloc1(struct sockaddr *dst, int report, u_long flags);
void
rtalloc(struct route *ro);
void
rtalloc_ign(struct route *ro, u_long flags);
options RADIX_MPATH
DESCRIPTION
The kernel uses a radix tree structure to manage routes for the networking subsystem. If compiled with options RADIX_MPATH kernel may main-
tain 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
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 database (FIB) on which the lookup should be performed. In case of suc-
cess 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, free-
ing 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 rtalloc1_fib().
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.
LEGACY INTERFACE
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.
RETURN VALUES
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.
SEE ALSO
route(4), rtentry(9)
HISTORY
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.
AUTHORS
The original version of this manual page was written by Garrett Wollman. It was significantly updated by Gleb Smirnoff.
BSD
July 4, 2012 BSD