topo-BAC: Factor out link-establishment into xlink

namespace_demo/lib.sh

 # lib.sh is library of common shell functions for topo-*
 
+PID=$$
+
 # `xunshare <dir> ...`  -- unshare net/mount/... namespaces to be referenced by dir
 xunshare() {
     ref=$1
@@ -16,3 +18,30 @@ xnsenter() {
     shift
     nsenter --mount=$ref/mnt --net=$ref/net --wd=. "$@"
 }
+
+
+# `xlink A B` sets up veth links in between nodes A and B going through bridge brAB:
+#
+#       A  ------- brAB -------  B
+#        a-b  brAB.a  brAB.b  b-a
+xlink() {
+    A=$1
+    B=$2
+    a="${A,,}" # A -> a
+    b="${B,,}" # B -> b
+
+    xnsenter $A -- ip link add $a-$b type veth peer br$A$B.$a
+    xnsenter $A -- ip link set br$A$B.$a netns $PID
+    xnsenter $A -- ip link set $a-$b up
+    ip link set br$A$B.$a up
+
+    xnsenter $B -- ip link add $b-$a type veth peer br$A$B.$b
+    xnsenter $B -- ip link set br$A$B.$b netns $PID
+    xnsenter $B -- ip link set $b-$a up
+    ip link set br$A$B.$b up
+
+    ip link add br$A$B type bridge # vlan_filtering 1 mcast_snooping 0
+    ip link set br$A$B.$a master br$A$B
+    ip link set br$A$B.$b master br$A$B
+    ip link set br$A$B up
+}

namespace_demo/topo-B-A-C.sh

@@ -2,10 +2,10 @@
 # topo B-A-C creates the following network topology:
 #
 #
-#     ns:B           tns:A            ns:C
+#     ns:B            ns:A            ns:C
 #
 #       B  --- br0 ---  A  --- br1 ---  C
-#        b1  B1   A1  a1 a2  A2   C1  c1
+#        b-a         a-b a-c         c-a
 #
 #
 # should be run under unshare -mrun .
@@ -15,56 +15,29 @@
 
 . lib.sh
 
-PID=$$
-
-# B-br0-A
-xunshare B -- ip link set lo up
-xnsenter B -- ip link add b1 type veth peer B1
-xnsenter B -- ip link set B1 netns $PID
-xnsenter B -- ip link set b1 up
-ip link set B1 up
 
+# lo on everything
 xunshare A -- ip link set lo up
-xnsenter A -- ip link add a1 type veth peer A1
-xnsenter A -- ip link set A1 netns $PID
-xnsenter A -- ip link set a1 up
-ip link set A1 up
-
-ip link add br0 type bridge # vlan_filtering 1 mcast_snooping 0
-ip link set B1 master br0
-ip link set A1 master br0
-ip link set br0 up
-
-# A-br1-C
-xnsenter A -- ip link add a2 type veth peer A2
-xnsenter A -- ip link set A2 netns $PID
-xnsenter A -- ip link set a2 up
-ip link set A2 up
-
+xunshare B -- ip link set lo up
 xunshare C -- ip link set lo up
-xnsenter C -- ip link add c1 type veth peer C1
-xnsenter C -- ip link set C1 netns $PID
-xnsenter C -- ip link set c1 up
-ip link set C1 up
 
-ip link add br1 type bridge # vlan_filtering 1 mcast_snooping 0
-ip link set C1 master br1
-ip link set A2 master br1
-ip link set br1 up
+# links
+xlink B A   # B-A
+xlink A C   # A-C
 
 
 # addresses
-xnsenter B -- ip addr add 10.0.0.1/24 dev b1
-xnsenter A -- ip addr add 10.0.0.2/24 dev a1
-xnsenter C -- ip addr add 20.0.0.1/24 dev c1
-xnsenter A -- ip addr add 20.0.0.2/24 dev a2
+xnsenter B -- ip addr add 10.0.0.1/24 dev b-a
+xnsenter A -- ip addr add 10.0.0.2/24 dev a-b
+xnsenter C -- ip addr add 20.0.0.1/24 dev c-a
+xnsenter A -- ip addr add 20.0.0.2/24 dev a-c
 
 # multicast routing
-xnsenter B -- ip route add 224.0.0.0/4 dev b1
-xnsenter C -- ip route add 224.0.0.0/4 dev c1
+xnsenter B -- ip route add 224.0.0.0/4 dev b-a
+xnsenter C -- ip route add 224.0.0.0/4 dev c-a
 
-xnsenter A -- ip route add    224.0.0.0/4 dev a1   # NOTE on A 224.0.0.0/4 is routed
-xnsenter A -- ip route append 224.0.0.0/4 dev a2   # to _both_ a1 and a2
+xnsenter A -- ip route add    224.0.0.0/4 dev a-b   # NOTE on A 224.0.0.0/4 is routed
+xnsenter A -- ip route append 224.0.0.0/4 dev a-c   # to _both_ a-b and a-c
 
 
 # mount private /var/run so that smcrouted can be started