From 8e50e0759df13a341f40a2221953506e1e0ceacb Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Tue, 23 Sep 2014 14:49:00 +0100
Subject: [PATCH] Make attach and detach idempotent

---
 weaver/weave | 38 ++++++++++++++++++++------------------
 1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/weaver/weave b/weaver/weave
index d7a617ed..de0e72e7 100755
--- a/weaver/weave
+++ b/weaver/weave
@@ -113,7 +113,6 @@ container_netns_preamble() {
         echo "Container $1 unknown to Docker." >&2
         exit 1
     }
-
     NSPID=$DOCKERPID
 
     [ ! -d /var/run/netns ] && mkdir -p /var/run/netns
@@ -133,20 +132,21 @@ container_netns_cleanup() {
 configure_container_networking() {
     container_netns_preamble $1
 
-    EXITCODE=1
-
     # If veth name already exists then assume we set it up already;
-    # just add the IP address
+    # just add the IP address, if it's not already there
     if ip link show $LOCAL_IFNAME >/dev/null 2>&1 ; then
-        if ip netns exec $NSPID ip addr add $2 dev $CONTAINER_IFNAME ; then
-            EXITCODE=0
-        else
-            echo "Failed to attach address $2 to container $1" >&2
+        if ! ip netns exec $NSPID ip addr list dev $CONTAINER_IFNAME | grep -qF $2 ; then
+            if ! ip netns exec $NSPID ip addr add $2 dev $CONTAINER_IFNAME ; then
+                echo "Failed to attach address $2 to container $1" >&2
+                container_netns_cleanup
+                return 1
+            fi
         fi
         container_netns_cleanup
-        return $EXITCODE
+        return 0
     fi
 
+    EXITCODE=1
     IP_TMPFILE=/tmp/weave_ip_output_$$
     rm -f $IP_TMPFILE
     if ip link add name $LOCAL_IFNAME mtu $MTU type veth peer name $GUEST_IFNAME mtu $MTU >$IP_TMPFILE 2>&1 ; then
@@ -185,19 +185,21 @@ detach() {
     container_netns_preamble $1
 
     EXITCODE=1
-    if ip netns exec $NSPID ip addr del $2 dev $CONTAINER_IFNAME ; then
-        # if no inet addresses remain then delete the veth
-        if [ -z "$(ip netns exec $NSPID ip -f inet addr list dev ethwe)" ] ; then
-            if ip link del $LOCAL_IFNAME type veth ; then
-                EXITCODE=0
+    if ip netns exec $NSPID ip addr list dev $CONTAINER_IFNAME | grep -qF $2 ; then
+        if ip netns exec $NSPID ip addr del $2 dev $CONTAINER_IFNAME ; then
+            # if no inet addresses remain then delete the veth
+            if [ -z "$(ip netns exec $NSPID ip -f inet addr list dev ethwe)" ] ; then
+                if ip link del $LOCAL_IFNAME type veth ; then
+                    EXITCODE=0
+                else
+                    echo "Failed to delete virtual ethernet device $LOCAL_IFNAME from container $1" >&2
+                fi
             else
-                echo "Failed to delete virtual ethernet device $LOCAL_IFNAME from container $1" >&2
+                EXITCODE=0
             fi
         else
-            EXITCODE=0
+            echo "Failed to detach address $2 from container $1" >&2
         fi
-    else
-        echo "Failed to detach address $2 from container $1" >&2
     fi
 
     container_netns_cleanup