tools/zep_dispatch: allow to pin nodes to MAC address

Positions in the topology are handed out first come first serve.
This makes it hard to have a reproducable setup if the ZEP dispatcher is
restarted (e.g. to modify the topology).

Fix this by allowing to specify a MAC address for each node.
If a node with a pinned MAC address connects, it will always be assigned to
the same topology node.

dist/tools/zep_dispatch/Makefile

@@ -21,6 +21,8 @@ RIOT_INCLUDE += -I$(RIOTBASE)/sys/include
 
 SRCS := $(wildcard *.c)
 SRCS += $(RIOTBASE)/sys/net/link_layer/ieee802154/ieee802154.c
+SRCS += $(RIOTBASE)/sys/fmt/fmt.c
+SRCS += $(RIOTBASE)/sys/net/link_layer/l2util/l2util.c
 
 $(BINARY): $(SRCS)
 	$(CC) $(CFLAGS) $(CFLAGS_EXTRA) $(SRCS) -o $@

dist/tools/zep_dispatch/example.topo

@@ -1,3 +1,6 @@
+# uncomment to pin node A to a specific MAC address
+# A := BA:7C:18:E4:C0:45:65:AF
+
 # A and B are connected with an ideal link
 A	B
 # A and C are connected with a symmetric link with 10% packet loss

dist/tools/zep_dispatch/topology.c

@@ -37,6 +37,8 @@ struct edge {
     float weight_b_a;
 };
 
+size_t l2util_addr_from_str(const char *str, uint8_t *out);
+
 static char *_fmt_addr(char *out, size_t out_len, const uint8_t *addr, uint8_t addr_len)
 {
     char *start = out;
@@ -70,9 +72,8 @@ static struct node *_find_or_create_node(list_node_t *nodes, const char *name)
     struct node *node = _find_node_by_name(nodes, name);
 
     if (node == NULL) {
-        node = malloc(sizeof(*node));
+        node = calloc(1, sizeof(*node));
         strncpy(node->name, name, sizeof(node->name) - 1);
-        node->mac_len = 0;
         list_add(nodes, &node->next);
     }
 
@@ -96,6 +97,17 @@ static bool _parse_line(char *line, list_node_t *nodes, list_node_t *edges)
         return false;
     }
 
+    /* add node with a defined MAC address */
+    if (strcmp(b, ":=") == 0) {
+        struct node *n = _find_or_create_node(nodes, a);
+        if (n == NULL) {
+            return false;
+        }
+
+        n->mac_len = l2util_addr_from_str(e_ab, n->mac);
+        return true;
+    }
+
     if (e_ab == NULL) {
         e_ab = "1";
     }
@@ -255,9 +267,16 @@ bool topology_add(topology_t *t, const uint8_t *mac, uint8_t mac_len,
             continue;
         }
 
-        /* abort if node is already in list */
+        /* node is already in the list - either it is connected or MAC was pinned */
         if (memcmp(super->mac, mac, mac_len) == 0) {
-            return true;
+            if (super->addr.sin6_port == addr->sin6_port) {
+                /* abort if node is already connected */
+                return true;
+            } else {
+                /* use pre-allocated node */
+                empty = super;
+                break;
+            }
         }
     }