From: Stefan Tomanek <redacted>
Date: Tue, 30 Jul 2013 09:46:36 +0200

This change adds a new operation to the fib_rules_ops struct; it allows the
suppression of routing decisions if certain criteria are not met by its
results.

The first implemented constraint is a minimum prefix length added to the
structures of routing rules. If a rule is added with a minimum prefix length

quoted

0, only routes meeting this threshold will be considered. Any other (more

general) routing table entries will be ignored.

When configuring a system with multiple network uplinks and default routes, it
is often convinient to reference the main routing table multiple times - but
omitting the default route. Using this patch and a modified "ip" utility, this
can be achieved by using the following command sequence:

  $ ip route add table secuplink default via 10.42.23.1

  $ ip rule add pref 100            table main prefixlength 1
  $ ip rule add pref 150 fwmark 0xA table secuplink

With this setup, packets marked 0xA will be processed by the additional routing
table "secuplink", but only if no suitable route in the main routing table can
be found. By using a minimal prefixlength of 1, the default route (/0) of the
table "main" is hidden to packets processed by rule 100; packets traveling to
destinations with more specific routing entries are processed as usual.

Signed-off-by: Stefan Tomanek <redacted>

I just want to mention that the more quirky crap we put into the FIB
rules layer, the harder it will every be to make a scalable data
structure for FIB rule handling.

Right now it's basically a linear walk of rules, with processing at
each level.

And every single ipv4 route lookup is going to go through this entire
process.

Anyways, there are coding style problems in your change which you'll
need to address:

+		if (!err && ops->suppress && ops->suppress(rule, arg)) {
+			continue;
+		}

Since statement basic blocks should not use curly braces.

+		if (!(arg->flags & FIB_LOOKUP_NOREF)) {
+			fib_info_put(result->fi);
+		}

Likewise.