table of contents
RTALLOC(9) | Kernel Developer's Manual | RTALLOC(9) |
NAME¶
rtalloc, rtalloc_ign, rtalloc1, rtfree — look up a route in the kernel routing tableSYNOPSIS¶
#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 networking 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.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flag is obsolete and thus ignored by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, requesting 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; };
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 performing 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 caller does
not want to receive the returned rtentry locked. The
ro argument is the same as rtalloc(),
but there is additionally a flags argument, which is now
only used to pass RTF_RNH_LOCKED
indicating that the
radix tree lock is already held. 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
”. Instead, it takes a “struct
sockaddr *
” directly as the sa argument.
The second argument, report, controls whether the lower
layers are notified when a lookup fails. 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 allocated by rtalloc1().
The RTFREE() macro is used to free unlocked route entries,
previously allocated 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 entry if it succeeds, otherwise a null pointer. Lack of a route should in most cases be translated to the errno(2) valueEHOSTUNREACH
.
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.AUTHORS¶
This manual page was written by Garrett Wollman, as were the changes to implementRTF_PRCLONING
and the
rtalloc_ign() function and the flags
argument to rtalloc1().December 11, 2008 | Debian |