BFD-FIB interactions

- single-hop BFD: attach a delegate to the appropriate adjacency
- multi-hop BFD [not supported yet]: attach a delegate to the FIB entry.

adjacency/fib_entry state tracks the BFD session state. when the state is down the object does not contribute forwarding hence and hence dependent objects will not use it.
For example, if a route is ECMP via two adjacencies and one of them is BFD down, then only the other is used to forward (i.e. we don't drop half the traffic).

Change-Id: I0ef53e20e73b067001a132cd0a3045408811a822
Signed-off-by: Neale Ranns <nranns@cisco.com>

1 files changed, 184 insertions, 0 deletions

diff --git a/src/vnet/adj/adj_bfd.c b/src/vnet/adj/adj_bfd.c
new file mode 100644
index 00000000000..3d294c4646e
--- /dev/null
+++ b/src/vnet/adj/adj_bfd.c
@@ -0,0 +1,184 @@
+/*
+ * Copyright (c) 2016 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <vnet/bfd/bfd_main.h>
+
+#include <vnet/adj/adj_delegate.h>
+#include <vnet/adj/adj_nbr.h>
+#include <vnet/fib/fib_walk.h>
+
+static adj_bfd_state_t
+adj_bfd_bfd_state_to_fib (bfd_state_e bstate)
+{
+    switch (bstate)
+    {
+    case BFD_STATE_up:
+        return (ADJ_BFD_STATE_UP);
+    case BFD_STATE_down:
+    case BFD_STATE_admin_down:
+    case BFD_STATE_init:
+        return (ADJ_BFD_STATE_DOWN);
+    }
+    return (ADJ_BFD_STATE_DOWN);
+}
+
+static void
+adj_bfd_update_walk (adj_index_t ai)
+{
+    /*
+     * initiate a backwalk of dependent children
+     * to notify of the state change of this adj.
+     */
+    fib_node_back_walk_ctx_t ctx = {
+        .fnbw_reason = FIB_NODE_BW_REASON_FLAG_ADJ_UPDATE,
+    };
+    fib_walk_sync(FIB_NODE_TYPE_ADJ, ai, &ctx);
+}
+
+/**
+ * @brief Callback function registered with BFD module to receive notifications
+ * of the CRUD of BFD sessions
+ * would be static but for the fact it's called from the unit-tests
+ */
+void
+adj_bfd_notify (bfd_listen_event_e event,
+                const bfd_session_t *session)
+{
+    const bfd_udp_key_t *key;
+    fib_protocol_t fproto;
+    adj_delegate_t *aed;
+    adj_index_t ai;
+
+    if (BFD_HOP_TYPE_SINGLE != session->hop_type)
+    {
+        /*
+         * multi-hop BFD sessions attach directly to the FIB entry
+         * single-hop adj to the associate adjacency.
+         */
+        return;
+    }
+
+    key = &session->udp.key;
+
+    fproto = (ip46_address_is_ip4 (&key->peer_addr) ?
+              FIB_PROTOCOL_IP4:
+              FIB_PROTOCOL_IP6);
+
+    /*
+     * find the adj that corresponds to the BFD session.
+     */
+    ai = adj_nbr_add_or_lock(fproto,
+                             fib_proto_to_link(fproto),
+                             &key->peer_addr,
+                             key->sw_if_index);
+
+    switch (event)
+    {
+    case BFD_LISTEN_EVENT_CREATE:
+        /*
+         * The creation of a new session
+         */
+        if ((ADJ_INDEX_INVALID != ai) &&
+            (aed = adj_delegate_get(adj_get(ai),
+                                    ADJ_DELEGATE_BFD)))
+        {
+            /*
+             * already got state for this adj
+             */
+        }
+        else
+        {
+            /*
+             * lock the adj. add the delegate.
+             * Lockinging the adj prevents it being removed and thus maintains
+             * the BFD derived states
+             */
+            adj_lock(ai);
+
+            aed = adj_delegate_find_or_add(adj_get(ai), ADJ_DELEGATE_BFD);
+
+            /*
+             * pretend the session is up and skip the walk.
+             * If we set it down then we get traffic loss on new children.
+             * if we walk then we lose traffic for existing children. Wait
+             * for the first BFD UP/DOWN before we let the session's state
+             * influence forwarding.
+             */
+            aed->ad_bfd_state = ADJ_BFD_STATE_UP;
+            aed->ad_bfd_index = session->bs_idx;
+        }
+        break;
+
+    case BFD_LISTEN_EVENT_UPDATE:
+        /*
+         * state change up/dowm and
+         */
+        aed = adj_delegate_get(adj_get(ai), ADJ_DELEGATE_BFD);
+
+        if (NULL != aed)
+        {
+            aed->ad_bfd_state = adj_bfd_bfd_state_to_fib(session->local_state);
+            adj_bfd_update_walk(ai);
+        }
+        /*
+         * else
+         *   not an adj with BFD state
+         */
+        break;
+
+    case BFD_LISTEN_EVENT_DELETE:
+        /*
+         * session has been removed.
+         */
+
+        if (adj_delegate_get(adj_get(ai), ADJ_DELEGATE_BFD))
+        {
+            /*
+             * has an associated BFD tracking delegate
+             * remove the BFD tracking deletgate, update children, then
+             * unlock the adj
+             */
+            adj_delegate_remove(adj_get(ai), ADJ_DELEGATE_BFD);
+
+            adj_bfd_update_walk(ai);
+            adj_unlock(ai);
+        }
+        /*
+         * else
+         *  no BFD associated state
+         */
+        break;
+    }
+
+    /*
+     * unlock match of the add-or-lock at the start
+     */
+    adj_unlock(ai);
+}
+
+static clib_error_t *
+adj_bfd_main_init (vlib_main_t * vm)
+{
+    clib_error_t * error = NULL;
+
+    if ((error = vlib_call_init_function (vm, bfd_main_init)))
+        return (error);
+
+    bfd_register_listener(adj_bfd_notify);
+
+    return (error);
+}
+
+VLIB_INIT_FUNCTION (adj_bfd_main_init);