Use sysfs to set hairpin mode

Set the hairpin mode using the sysfs interface which
looks like it is working all the way to the oldest
of RHEL6.6 kernels.

Signed-off-by: Jana Radhakrishnan <mrjana@docker.com>

Makefile

@@ -40,6 +40,7 @@ check-format:
 
 run-tests:
 	@echo "Running tests... "
+	@sudo mount -o rw,remount -t sysfs sysfs /sys
 	@echo "mode: count" > coverage.coverprofile
 	@for dir in $$(find . -maxdepth 10 -not -path './.git*' -not -path '*/_*' -type d); do \
 	    if ls $$dir/*.go &> /dev/null; then \
@@ -49,15 +50,15 @@ run-tests:
 		ret=$$? ;\
 		if [ $$ret -ne 0 ]; then exit $$ret; fi ;\
 		popd &> /dev/null; \
-	        if [ -f $$dir/profile.tmp ]; then \
-		        cat $$dir/profile.tmp | tail -n +2 >> coverage.coverprofile ; \
+		if [ -f $$dir/profile.tmp ]; then \
+			cat $$dir/profile.tmp | tail -n +2 >> coverage.coverprofile ; \
 				rm $$dir/profile.tmp ; \
-            fi ; \
-        fi ; \
+	    fi ; \
+	fi ; \
 	done
 	@echo "Done running tests"
 
-check-local: 	check-format check-code run-tests 
+check-local:	check-format check-code run-tests
 
 install-deps:
 	apt-get update && apt-get -y install iptables

circle.yml

@@ -1,12 +1,13 @@
 machine:
     services:
         - docker
-
+    post:
+        - sudo mount -o rw,remount -t sysfs sysfs /sys
+
 dependencies:
     override:
         - echo "Nothing to install"
 
 test:
     override:
-        - make circle-ci
-
+        - sudo make circle-ci

drivers/bridge/bridge.go

@@ -3,8 +3,10 @@ package bridge
 import (
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"net"
 	"os/exec"
+	"path/filepath"
 	"strconv"
 	"sync"
 
@@ -772,6 +774,23 @@ func addToBridge(ifaceName, bridgeName string) error {
 	return ioctlAddToBridge(iface, master)
 }
 
+func setHairpinMode(ifaceName string, enable bool) error {
+	path := filepath.Join("/sys/class/net", ifaceName, "brport/hairpin_mode")
+
+	var val []byte
+	if enable {
+		val = []byte{'1', '\n'}
+	} else {
+		val = []byte{'0', '\n'}
+	}
+
+	if err := ioutil.WriteFile(path, val, 0644); err != nil {
+		return fmt.Errorf("unable to set hairpin mode on %s: %v", ifaceName, err)
+	}
+
+	return nil
+}
+
 func (d *driver) CreateEndpoint(nid, eid types.UUID, epInfo driverapi.EndpointInfo, epOptions map[string]interface{}) error {
 	var (
 		ipv6Addr *net.IPNet
@@ -902,7 +921,7 @@ func (d *driver) CreateEndpoint(nid, eid types.UUID, epInfo driverapi.EndpointIn
 	}
 
 	if !config.EnableUserlandProxy {
-		err = netlink.LinkSetHairpin(host, true)
+		err = setHairpinMode(hostIfName, true)
 		if err != nil {
 			return err
 		}

netutils/test_utils.go

@@ -32,6 +32,14 @@ func SetupTestNetNS(t *testing.T) func() {
 		t.Fatal("Failed to open netns file")
 	}
 
+	if err := syscall.Unmount("/sys", syscall.MNT_DETACH); err != nil {
+		t.Fatalf("unmount /sys failed: %v", err)
+	}
+
+	if err := syscall.Mount("sysfs", "/sys", "sysfs", 0, ""); err != nil {
+		t.Fatalf("remount sysfs within netns failed: %v", err)
+	}
+
 	return func() {
 		if err := syscall.Close(fd); err != nil {
 			t.Logf("Warning: netns closing failed (%v)", err)