From a6a822268c637bc99ff5f7967e3a9d757e504ea0 Mon Sep 17 00:00:00 2001
From: Eugene Yakubovich <eugene.yakubovich@coreos.com>
Date: Tue, 19 May 2015 12:02:41 -0700
Subject: [PATCH] add DHCP IPAM plugin

The plugin binary actually functions in two modes. The first mode
is a regular CNI plugin. The second mode (when stared with "daemon" arg)
runs a DHCP client daemon. When executed as a CNI plugin, it issues
an RPC request to the daemon for actual processing. The daemon is
required since a DHCP lease needs to be maintained by periodically
renewing it. One instance of the daemon can server arbitrary number
of containers/leases.
---
 ns/ns.go | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/ns/ns.go b/ns/ns.go
index 82291f98..20548b9b 100644
--- a/ns/ns.go
+++ b/ns/ns.go
@@ -48,19 +48,30 @@ func SetNS(f *os.File, flags uintptr) error {
 
 // WithNetNSPath executes the passed closure under the given network
 // namespace, restoring the original namespace afterwards.
-func WithNetNSPath(nspath string, f func(*os.File) error) error {
+// Changing namespaces must be done on a goroutine that has been
+// locked to an OS thread. If lockThread arg is true, this function
+// locks the goroutine prior to change namespace and unlocks before
+// returning
+func WithNetNSPath(nspath string, lockThread bool, f func(*os.File) error) error {
 	ns, err := os.Open(nspath)
 	if err != nil {
 		return fmt.Errorf("Failed to open %v: %v", nspath, err)
 	}
 	defer ns.Close()
-
-	return WithNetNS(ns, f)
+	return WithNetNS(ns, lockThread, f)
 }
 
 // WithNetNS executes the passed closure under the given network
 // namespace, restoring the original namespace afterwards.
-func WithNetNS(ns *os.File, f func(*os.File) error) error {
+// Changing namespaces must be done on a goroutine that has been
+// locked to an OS thread. If lockThread arg is true, this function
+// locks the goroutine prior to change namespace and unlocks before
+// returning
+func WithNetNS(ns *os.File, lockThread bool, f func(*os.File) error) error {
+	if lockThread {
+		runtime.LockOSThread()
+		defer runtime.UnlockOSThread()
+	}
 	// save a handle to current (host) network namespace
 	thisNS, err := os.Open("/proc/self/ns/net")
 	if err != nil {