fib: only update glean for interface if necessary

Type: improvement

If an interface address is added, the glean adjacency for it's covering
prefix is updated with that address. In the case of multiple addresses
within the same prefix being added, the most recently added one will end
up being used as the sender protocol address for ARP requests.

Similar behavior occurs when an interface address is deleted. The glean
adjacency is updated to some appropriate entry under it's covering
prefix. If there were multiple interface addresses configured, we may
update the address on the adjacency even though the address currently in
use is not the one being deleted.

Add a new value PROVIDES_GLEAN to fib_entry_src_flag_t. The flag
identifies whether a source interface entry is being used as the address
for the glean adjacency for the covering prefix.

Update logic so that the glean is only updated on adding an interface
address if there is not already a sibling entry in use which has the
flag set. Also, only update the glean on deleting an interface address
if the address being deleted has the flag set.

Also update unit test which validates expected behavior in the case
where multiple addresses within a prefix are configured on an interface.

Signed-off-by: Matthew Smith <mgsmith@netgate.com>
Change-Id: I7d918b8dd703735b20ec76e0a60af6d7e571b766
(cherry picked from commit 9e5694b405e0200725a993f0c17d452fab508435)

3 files changed, 93 insertions, 17 deletions

diff --git a/src/vnet/fib/fib_entry.h b/src/vnet/fib/fib_entry.h
index 223928354b7..7331f803ec4 100644
--- a/src/vnet/fib/fib_entry.h
+++ b/src/vnet/fib/fib_entry.h
@@ -154,9 +154,13 @@ typedef enum fib_entry_src_attribute_t_ {
      */
     FIB_ENTRY_SRC_ATTRIBUTE_INHERITED,
     /**
+     * the source is currently used as glean src address
+     */
+    FIB_ENTRY_SRC_ATTRIBUTE_PROVIDES_GLEAN,
+    /**
      * Marker. add new entries before this one.
      */
-    FIB_ENTRY_SRC_ATTRIBUTE_LAST = FIB_ENTRY_SRC_ATTRIBUTE_INHERITED,
+    FIB_ENTRY_SRC_ATTRIBUTE_LAST = FIB_ENTRY_SRC_ATTRIBUTE_PROVIDES_GLEAN,
 } fib_entry_src_attribute_t;
 
 
@@ -166,6 +170,7 @@ typedef enum fib_entry_src_attribute_t_ {
     [FIB_ENTRY_SRC_ATTRIBUTE_ACTIVE] = "active", \
     [FIB_ENTRY_SRC_ATTRIBUTE_STALE] = "stale",      \
     [FIB_ENTRY_SRC_ATTRIBUTE_INHERITED] = "inherited", \
+    [FIB_ENTRY_SRC_ATTRIBUTE_PROVIDES_GLEAN] = "provides-glean", \
 }
 
 #define FOR_EACH_FIB_SRC_ATTRIBUTE(_item)      		\
@@ -180,6 +185,7 @@ typedef enum fib_entry_src_flag_t_ {
     FIB_ENTRY_SRC_FLAG_ACTIVE = (1 << FIB_ENTRY_SRC_ATTRIBUTE_ACTIVE),
     FIB_ENTRY_SRC_FLAG_STALE = (1 << FIB_ENTRY_SRC_ATTRIBUTE_STALE),
     FIB_ENTRY_SRC_FLAG_INHERITED = (1 << FIB_ENTRY_SRC_ATTRIBUTE_INHERITED),
+    FIB_ENTRY_SRC_FLAG_PROVIDES_GLEAN = (1 << FIB_ENTRY_SRC_ATTRIBUTE_PROVIDES_GLEAN),
 } __attribute__ ((packed)) fib_entry_src_flag_t;
 
 extern u8 * format_fib_entry_src_flags(u8 *s, va_list *args);
diff --git a/src/vnet/fib/fib_entry_src_interface.c b/src/vnet/fib/fib_entry_src_interface.c
index 402369d1dfc..c5028dc8798 100644
--- a/src/vnet/fib/fib_entry_src_interface.c
+++ b/src/vnet/fib/fib_entry_src_interface.c
@@ -87,8 +87,16 @@ fib_entry_src_interface_update_glean (fib_entry_t *cover,
             if (fib_prefix_is_cover(&adj->sub_type.glean.rx_pfx,
                                     &local->fe_prefix))
             {
-                adj->sub_type.glean.rx_pfx.fp_addr = local->fe_prefix.fp_addr;
-                return (1);
+		fib_entry_src_t *local_src;
+
+		local_src = fib_entry_src_find (local, FIB_SOURCE_INTERFACE);
+		if (local_src != NULL)
+		  {
+		    adj->sub_type.glean.rx_pfx.fp_addr =
+		      local->fe_prefix.fp_addr;
+		    local_src->fes_flags |= FIB_ENTRY_SRC_FLAG_PROVIDES_GLEAN;
+		    return (1);
+		  }
             }
         }
     }
@@ -116,6 +124,52 @@ fib_entry_src_interface_path_swap (fib_entry_src_t *src,
     src->fes_pl = fib_path_list_create(pl_flags, paths);
 }
 
+typedef struct fesi_find_glean_ctx_t_ {
+  fib_node_index_t glean_node_index;
+} fesi_find_glean_ctx_t;
+
+static walk_rc_t
+fib_entry_src_interface_find_glean_walk (fib_entry_t *cover,
+					 fib_node_index_t covered,
+					 void *ctx)
+{
+  fesi_find_glean_ctx_t *find_glean_ctx = ctx;
+  fib_entry_t *covered_entry;
+  fib_entry_src_t *covered_src;
+
+  covered_entry = fib_entry_get (covered);
+  covered_src = fib_entry_src_find (covered_entry, FIB_SOURCE_INTERFACE);
+  if ((covered_src != NULL) &&
+      (covered_src->fes_flags & FIB_ENTRY_SRC_FLAG_PROVIDES_GLEAN))
+    {
+      find_glean_ctx->glean_node_index = covered;
+      return WALK_STOP;
+    }
+
+  return WALK_CONTINUE;
+}
+
+static fib_entry_t *
+fib_entry_src_interface_find_glean (fib_entry_t *cover)
+{
+  fib_entry_src_t *src;
+
+  src = fib_entry_src_find (cover, FIB_SOURCE_INTERFACE);
+  if (src == NULL)
+    /* the cover is not an interface source */
+    return NULL;
+
+  fesi_find_glean_ctx_t ctx = {
+    .glean_node_index = ~0,
+  };
+
+  fib_entry_cover_walk (cover, fib_entry_src_interface_find_glean_walk,
+			&ctx);
+
+  return (ctx.glean_node_index == ~0) ? NULL :
+					fib_entry_get (ctx.glean_node_index);
+}
+
 /*
  * Source activate. 
  * Called when the source is teh new longer best source on the entry
@@ -128,6 +182,8 @@ fib_entry_src_interface_activate (fib_entry_src_t *src,
 
     if (FIB_ENTRY_FLAG_LOCAL & src->fes_entry_flags)
     {
+	u8 update_glean;
+
 	/*
 	 * Track the covering attached/connected cover. This is so that
 	 * during an attached export of the cover, this local prefix is
@@ -141,10 +197,17 @@ fib_entry_src_interface_activate (fib_entry_src_t *src,
 
 	cover = fib_entry_get(src->u.interface.fesi_cover);
 
+	/*
+	 * Before adding as a child of the cover, check whether an existing
+	 * child has already been used to populate the glean adjacency. If so,
+	 * we don't need to update the adjacency.
+	 */
+	update_glean = (fib_entry_src_interface_find_glean (cover) == NULL);
 	src->u.interface.fesi_sibling =
 	    fib_entry_cover_track(cover, fib_entry_get_index(fib_entry));
 
-        fib_entry_src_interface_update_glean(cover, fib_entry);
+	if (update_glean)
+	  fib_entry_src_interface_update_glean(cover, fib_entry);
     }
 
     return (!0);
@@ -167,15 +230,19 @@ fib_entry_src_interface_deactivate (fib_entry_src_t *src,
     if (FIB_NODE_INDEX_INVALID != src->u.interface.fesi_cover)
     {
 	cover = fib_entry_get(src->u.interface.fesi_cover);
-
 	fib_entry_cover_untrack(cover, src->u.interface.fesi_sibling);
 
 	src->u.interface.fesi_cover = FIB_NODE_INDEX_INVALID;
 	src->u.interface.fesi_sibling = ~0;
 
-        fib_entry_cover_walk(cover,
-                             fib_entry_src_interface_update_glean_walk,
-                             NULL);
+	/* If this was the glean address, find a new one */
+	if (src->fes_flags & FIB_ENTRY_SRC_FLAG_PROVIDES_GLEAN)
+	  {
+	    fib_entry_cover_walk(cover,
+				fib_entry_src_interface_update_glean_walk,
+				NULL);
+	    src->fes_flags &= ~FIB_ENTRY_SRC_FLAG_PROVIDES_GLEAN;
+	  }
     }
 }
 
diff --git a/test/test_neighbor.py b/test/test_neighbor.py
index 041d78245a5..403e93ff2c4 100644
--- a/test/test_neighbor.py
+++ b/test/test_neighbor.py
@@ -2126,27 +2126,30 @@ class ARPTestCase(VppTestCase):
 
         #
         # add a local address in the same subnet
-        #  the source addresses are equivalent. VPP happens to
-        #  choose the last one that was added
+        #  the source addresses are equivalent.
+        # VPP leaves the glean address being used for a prefix
+        # in place until that address is deleted.
+        #
         conn3 = VppIpInterfaceAddress(self, self.pg1, "10.0.1.2", 24).add_vpp_config()
 
         rxs = self.send_and_expect(self.pg0, [p2], self.pg1)
         for rx in rxs:
-            self.verify_arp_req(rx, self.pg1.local_mac, "10.0.1.2", "10.0.1.128")
+            self.verify_arp_req(rx, self.pg1.local_mac, "10.0.1.1", "10.0.1.128")
 
         #
-        # remove
+        # remove first address, which is currently in use
+        # the second address should be used now
         #
-        conn3.remove_vpp_config()
+        conn2.remove_vpp_config()
         rxs = self.send_and_expect(self.pg0, [p2], self.pg1)
         for rx in rxs:
-            self.verify_arp_req(rx, self.pg1.local_mac, "10.0.1.1", "10.0.1.128")
+            self.verify_arp_req(rx, self.pg1.local_mac, "10.0.1.2", "10.0.1.128")
 
         #
-        # add back, this time remove the first one
+        # add first address back. Second address should continue
+        # being used.
         #
-        conn3 = VppIpInterfaceAddress(self, self.pg1, "10.0.1.2", 24).add_vpp_config()
-
+        conn2 = VppIpInterfaceAddress(self, self.pg1, "10.0.1.1", 24).add_vpp_config()
         rxs = self.send_and_expect(self.pg0, [p2], self.pg1)
         for rx in rxs:
             self.verify_arp_req(rx, self.pg1.local_mac, "10.0.1.2", "10.0.1.128")