freebsd-dev/share/man/man9/rtalloc.9

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.Dd July 4, 2012
.Dt RTALLOC 9
.Os
.Sh NAME
.Nm rtalloc1_fib ,
.Nm rtalloc_ign_fib ,
.Nm rtalloc_fib
.Nd look up a route in the kernel routing table
.Sh SYNOPSIS
.In sys/types.h
.In sys/socket.h
.In net/route.h
.Ft "struct rtentry *"
.Fn rtalloc1_fib "struct sockaddr *dst" "int report" "u_long flags" "u_int fibnum"
.Ft void
.Fn rtalloc_fib "struct route *ro" "u_int fibnum"
.Ft void
.Fn rtalloc_ign_fib "struct route *ro" "u_long flags" "u_int fibnum"
.Fn RTFREE_LOCKED "struct rt_entry *rt"
.Fn RTFREE "struct rt_entry *rt"
.Fn RT_LOCK "struct rt_entry *rt"
.Fn RT_UNLOCK "struct rt_entry *rt"
.Fn RT_ADDREF "struct rt_entry *rt"
.Fn RT_REMREF "struct rt_entry *rt"
.Fn RO_RTFREE "struct route *ro"
.Ft void
.Fn rtfree "struct rt_entry *rt"
.Ft "struct rtentry *"
.Fn rtalloc1 "struct sockaddr *dst" "int report" "u_long flags"
.Ft void
.Fn rtalloc "struct route *ro"
.Ft void
.Fn rtalloc_ign "struct route *ro" "u_long flags"
.Pp
.Cd options RADIX_MPATH
.Sh DESCRIPTION
The kernel uses a radix tree structure to manage routes for the
networking subsystem.
If compiled with
.Cd options RADIX_MPATH
kernel may maintain several independent forwarding information databases (FIBs).
The
.Fn 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.
.Pp
The
.Fn rtalloc1_fib
function is the most general form of
.Fn rtalloc ,
and all of the other forms are implemented as calls to it.
It takes a
.Fa "struct sockaddr *"
directly as the
.Fa dst
argument.
The second argument,
.Fa report ,
controls whether the routing sockets are notified when a lookup fails.
The third argument,
.Fa flags ,
is a combination of
the following values:
.Bl -item -offset indent
.It
.Dv RTF_RNH_LOCKED
indicates that the radix tree lock is already held
.El
.Pp
The last argument
.Fa fibnum
specifies number of forwarding information database (FIB) on which
the lookup should be performed.
In case of success the
.Fn rtalloc1_fib
function returns a pointer to a locked
.Vt "struct rtentry"
with an additional reference.
.Pp
The
.Fn rtalloc_fib
is the most simple variant.
Its main argument is
.Fa ro ,
a pointer to a
.Fa "struct route" ,
which is defined as follows:
.Bd -literal -offset indent
struct route {
	struct rtentry *ro_rt;
	struct llentry *ro_lle;
	struct sockaddr ro_dst;
};
.Ed
.Pp
Thus, this function can only be used for address families which are
smaller than the default
.Ft "struct sockaddr" .
Before calling
.Fn rtalloc_fib
for the first time, callers should ensure that unused bits of the
structure are set to zero.
The second argument
.Fa fibnum
is FIB number.
In case of success of the
.Fn rtalloc_fib
the
.Fa ro_rt
points to a valid and unlocked
.Xr rtentry 9 ,
which has an additional reference put on it, freeing which is
responsibility of the caller.
On subsequent calls,
.Fn rtalloc_fib
returns without performing a lookup if
.Fa ro->ro_rt
is non-null and the
.Dv RTF_UP
flag is set in the rtentry's
.Fa rt_flags
field.
.Pp
The
.Fn rtalloc_ign_fib
function is the same as the
.Fn rtalloc_fib ,
but there is additional
.Fa flags
argument, which is same as in
.Fn rtalloc1_fib .
.Pp
The
.Fn RTFREE_LOCKED
macro is used to unref and possibly free a locked routing entry
with one our reference, for example previously allocated by
.Fn rtalloc1_fib .
.Pp
The
.Fn RTFREE
macro is used to unref and possibly free an unlocked route entries with
one our reference, for example previously allocated by
.Fn rtalloc_fib
or
.Fn rtalloc_ign_fib .
.Pp
Both
.Fn RTFREE_LOCKED
and
.Fn RTFREE
macros decrement the reference count on the routing table entry,
and proceed with actual freeing if the reference count has reached zero.
.Pp
The
.Fn RT_LOCK
macro is used to lock a routing table entry.
.Pp
The
.Fn RT_UNLOCK
macro is used to unlock a routing table entry.
.Pp
The
.Fn RT_ADDREF
macro increments the reference count on a previously locked route entry.
It should be used whenever a reference to an
.Xr rtentry 9
is going to be stored outside the routing table.
.Pp
The
.Fn RT_REMREF
macro decrements the reference count on a previously locked route entry.
Its usage is contrary to
.Fn RT_ADDREF .
.Pp
The
.Fn 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
.Fn RO_RTFREE
treats such routes correctly.
.Pp
The
.Fn 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.
.Sh LEGACY INTERFACE
Prior to introduction of multiple routing tables functions did not
require the
.Fa "u_int fibnum"
argument.
Legacy
.Fn rtalloc1 ,
.Fn rtalloc
and
.Fn rtalloc_ign
functions are kept for compatibility, and are equivalent to
calling new interface with
.Fa fibnum
argument equal to
.Va 0 ,
which implies default forwarding table.
.Sh RETURN VALUES
The
.Fn rtalloc1_fib
function returns a pointer to a locked routing-table entry if it succeeds,
otherwise a null pointer.
The
.Fn rtalloc_fib
and
.Fn rtalloc_ign_fib
functions do not return a value, but they fill in the
.Fa *ro_rt
member of the
.Fa *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
.Xr errno 2
value
.Er EHOSTUNREACH .
.Sh SEE ALSO
.Xr route 4 ,
.Xr rtentry 9
.Sh HISTORY
The
.Nm rtalloc
facility first appeared in
.Bx 4.2 ,
although with much different internals.
The
.Fn rtalloc_ign
function and the
.Fa flags
argument to
.Fn rtalloc1
first appeared in
.Fx 2.0 .
Routing table locking was introduced in
.Fx 5.2 .
Multiple routing tables were introduced in
.Fx 8.0 .
.Sh AUTHORS
The original version of this manual page was written by
.An -nosplit
.An "Garrett Wollman" .
It was significantly updated by
.An "Gleb Smirnoff" .