RTALLOC(9) FreeBSD 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
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
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
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
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.
FreeBSD 13.1-RELEASE-p6 July 4, 2012 FreeBSD 13.1-RELEASE-p6
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