route-table: Allow parsing routes without nexthop.

A recent commit[0] added condition to "route_table_parse__" function that
causes it to throw error when parsing route without "nexthop
information" (either RTA_OIF, RTA_GATEWAY, RTA_VIA or RTA_MULTIPATH). While
this requirement is reasonable for regular routes, there are some route types
that don't need nexthop. One of these types is "blackhole" route, that we intend
to use in OVN for route advertising (RTN_BLACKHOLE)[1].

This change does not enforce the above-mentioned condition for those special
route types that don't require "nexthop information".

[0] openvswitch@91fc511
[1] https://mail.openvswitch.org/pipermail/ovs-dev/2025-January/419383.html

Signed-off-by: Martin Kalcok <[email protected]>
Signed-off-by: 0-day Robot <[email protected]>

lib/route-table.c

@@ -220,6 +220,24 @@ route_table_reset(void)
     }
 }
 
+
+/* Returns true if the given route requires nexhop information (output
+   interface, nexthop IP, ...). Returns false for special route types, like
+   blackhole, that don't need this information.
+ */
+static bool
+route_needs_nexthop(const struct rtmsg *rtm) {
+    switch (rtm->rtm_type) {
+        case RTN_BLACKHOLE:
+        case RTN_THROW:
+        case RTN_UNREACHABLE:
+        case RTN_PROHIBIT:
+            return false;
+        default:
+            return true;
+    }
+}
+
 static int
 route_table_parse__(struct ofpbuf *buf, size_t ofs,
                     const struct nlmsghdr *nlmsg,
@@ -430,7 +448,7 @@ route_table_parse__(struct ofpbuf *buf, size_t ofs,
                                        &mp_change.rd.nexthops);
             }
         }
-        if (!attrs[RTA_OIF] && !attrs[RTA_GATEWAY]
+        if (route_needs_nexthop(rtm) && !attrs[RTA_OIF] && !attrs[RTA_GATEWAY]
                 && !attrs[RTA_VIA] && !attrs[RTA_MULTIPATH]) {
             VLOG_DBG_RL(&rl, "route message needs an RTA_OIF, RTA_GATEWAY, "
                              "RTA_VIA or RTA_MULTIPATH attribute");