Merge pull request #2541 from weaveworks/issues/2540-withnetns

Change namespace via nsenter, for plugin arp-config step

common/utils.go

@@ -6,7 +6,6 @@ import (
 	"os"
 	"strings"
 
-	"github.com/j-keck/arping"
 	"github.com/vishvananda/netlink"
 	"github.com/vishvananda/netns"
 
@@ -167,20 +166,3 @@ func GetBridgeNetDev(bridgeName string) (NetDev, error) {
 
 	return linkToNetDev(link)
 }
-
-// Do post-attach configuration of all veths we have created
-func ConfigureARPforVeths(processID int, prefix string) error {
-	_, err := FindNetDevs(processID, func(link netlink.Link) bool {
-		ifName := link.Attrs().Name
-		if strings.HasPrefix(ifName, prefix) {
-			weavenet.ConfigureARPCache(ifName)
-			if addrs, err := netlink.AddrList(link, netlink.FAMILY_V4); err == nil {
-				for _, addr := range addrs {
-					arping.GratuitousArpOverIfaceByName(addr.IPNet.IP, ifName)
-				}
-			}
-		}
-		return false
-	})
-	return err
-}

net/netns.go

@@ -1,7 +1,10 @@
 package net
 
 import (
+	"bytes"
 	"errors"
+	"fmt"
+	"os/exec"
 	"runtime"
 
 	"github.com/vishvananda/netlink"
@@ -63,3 +66,27 @@ func WithNetNSLinkByPidUnsafe(pid int, ifName string, work func(link netlink.Lin
 
 	return WithNetNSLinkUnsafe(ns, ifName, work)
 }
+
+// A safe version of WithNetNS* which creates a process executing
+// "nsenter --net=<ns-path> weaveutil <cmd> [args]".
+func WithNetNS(nsPath string, cmd string, args ...string) (string, error) {
+	var stdout, stderr bytes.Buffer
+
+	args = append([]string{"--net=" + nsPath, "weaveutil", cmd}, args...)
+	c := exec.Command("nsenter", args...)
+	c.Stdout = &stdout
+	c.Stderr = &stderr
+	if err := c.Run(); err != nil {
+		return "", fmt.Errorf("%s: %s", string(stderr.Bytes()), err)
+	}
+
+	return string(stdout.Bytes()), nil
+}
+
+func WithNetNSByPid(pid int, cmd string, args ...string) (string, error) {
+	return WithNetNS(NSPathByPid(pid), cmd, args...)
+}
+
+func NSPathByPid(pid int) string {
+	return fmt.Sprintf("/proc/%d/ns/net", pid)
+}

plugin/net/watcher.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 
 	weaveapi "github.com/weaveworks/weave/api"
-	"github.com/weaveworks/weave/common"
 	"github.com/weaveworks/weave/common/docker"
 	weavenet "github.com/weaveworks/weave/net"
 )
@@ -46,7 +45,7 @@ func (w *watcher) ContainerStarted(id string) {
 			if err := w.weave.RegisterWithDNS(id, fqdn, net.IPAddress); err != nil {
 				w.driver.warn("ContainerStarted", "unable to register %s with weaveDNS: %s", id, err)
 			}
-			if err := common.ConfigureARPforVeths(info.State.Pid, weavenet.VethName); err != nil {
+			if _, err := weavenet.WithNetNSByPid(info.State.Pid, "configure-arp", weavenet.VethName); err != nil {
 				w.driver.warn("ContainerStarted", "unable to configure interfaces: %s", err)
 			}
 		}

prog/weaveutil/main.go

@@ -23,6 +23,7 @@ func init() {
 		"process-addrs":          processAddrs,
 		"attach-container":       attach,
 		"detach-container":       detach,
+		"configure-arp":          configureARP,
 	}
 }
 

prog/weaveutil/netdev.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"strings"
+
+	"github.com/j-keck/arping"
+	"github.com/vishvananda/netlink"
+
+	weavenet "github.com/weaveworks/weave/net"
+)
+
+func configureARP(args []string) error {
+	if len(args) != 1 {
+		cmdUsage("configure-arp", "<iface-name-prefix>")
+	}
+	prefix := args[0]
+
+	links, err := netlink.LinkList()
+	if err != nil {
+		return err
+	}
+	for _, link := range links {
+		ifName := link.Attrs().Name
+		if strings.HasPrefix(ifName, prefix) {
+			weavenet.ConfigureARPCache(ifName)
+			if addrs, err := netlink.AddrList(link, netlink.FAMILY_V4); err == nil {
+				for _, addr := range addrs {
+					arping.GratuitousArpOverIfaceByName(addr.IPNet.IP, ifName)
+				}
+			}
+		}
+	}
+
+	return nil
+}