ovs-vswitchd: Do not use system routing table with --disable-system.

The --disable-system option indicates that the user wants to avoid using
the host's datapath.  This is also a good indication that the user does
not want to use other host resources such as the routing table, so this
commit implements that.

This fixes a failure in the test "ptap - recirculate after packet_type
change" when the host routing table contained an entry that affected the
generated flow.  Without this patch, the commands:

led to a failure in that test.

Reported-by: Timothy Redaelli <tredaelli@redhat.com>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2018-March/046406.html
Tested-By: Timothy Redaelli <tredaelli@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

lib/ovs-router.c

@@ -54,6 +54,10 @@ static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
 static struct ovs_mutex mutex = OVS_MUTEX_INITIALIZER;
 static struct classifier cls;
 
+/* By default, use the system routing table.  For system-independent testing,
+ * the unit tests disable using the system routing table. */
+static bool use_system_routing_table = true;
+
 struct ovs_router_entry {
     struct cls_rule cr;
     char output_bridge[IFNAMSIZ];
@@ -71,13 +75,22 @@ ovs_router_entry_cast(const struct cls_rule *cr)
     return cr ? CONTAINER_OF(cr, struct ovs_router_entry, cr) : NULL;
 }
 
+/* Disables obtaining routes from the system routing table, for testing
+ * purposes. */
+void
+ovs_router_disable_system_routing_table(void)
+{
+    use_system_routing_table = false;
+}
+
 static bool
 ovs_router_lookup_fallback(const struct in6_addr *ip6_dst, char output_bridge[],
                            struct in6_addr *src6, struct in6_addr *gw6)
 {
     ovs_be32 src;
 
-    if (!route_table_fallback_lookup(ip6_dst, output_bridge, gw6)) {
+    if (!use_system_routing_table
+        || !route_table_fallback_lookup(ip6_dst, output_bridge, gw6)) {
         return false;
     }
     if (netdev_get_in4_by_name(output_bridge, (struct in_addr *)&src)) {
@@ -238,7 +251,9 @@ void
 ovs_router_insert(uint32_t mark, const struct in6_addr *ip_dst, uint8_t plen,
                   const char output_bridge[], const struct in6_addr *gw)
 {
-    ovs_router_insert__(mark, plen, ip_dst, plen, output_bridge, gw);
+    if (use_system_routing_table) {
+        ovs_router_insert__(mark, plen, ip_dst, plen, output_bridge, gw);
+    }
 }
 
 static void

lib/ovs-router.h

@@ -34,6 +34,9 @@ void ovs_router_insert(uint32_t mark, const struct in6_addr *ip_dst,
                        uint8_t plen,
                        const char output_bridge[], const struct in6_addr *gw);
 void ovs_router_flush(void);
+
+void ovs_router_disable_system_routing_table(void);
+
 #ifdef  __cplusplus
 }
 #endif

vswitchd/ovs-vswitchd.c

@@ -38,6 +38,7 @@
 #include "openflow/openflow.h"
 #include "ovsdb-idl.h"
 #include "ovs-rcu.h"
+#include "ovs-router.h"
 #include "openvswitch/poll-loop.h"
 #include "simap.h"
 #include "stream-ssl.h"
@@ -219,6 +220,7 @@ parse_options(int argc, char *argv[], char **unixctl_pathp)
 
         case OPT_DISABLE_SYSTEM:
             dp_blacklist_provider("system");
+            ovs_router_disable_system_routing_table();
             break;
 
         case '?':