libnetwork: Clean up sysfs-based operations

- The oldest kernel version currently supported is v3.10. Bridge
parameters can be set through netlink since v3.8 (see
torvalds/linux@25c71c7). As such, we don't need to fallback to sysfs to
set hairpin mode.
- `scanInterfaceStats()` is never called, so no need to keep it alive.
- Document why `default_pvid` is set through sysfs

Signed-off-by: Albin Kerouanton <albinker@gmail.com>

libnetwork/drivers/bridge/bridge.go

@@ -9,10 +9,8 @@ import (
 	"net"
 	"os"
 	"os/exec"
-	"path/filepath"
 	"strconv"
 	"sync"
-	"syscall"
 
 	"github.com/docker/docker/libnetwork/datastore"
 	"github.com/docker/docker/libnetwork/discoverapi"
@@ -891,32 +889,10 @@ func addToBridge(nlh *netlink.Handle, ifaceName, bridgeName string) error {
 
 func setHairpinMode(nlh *netlink.Handle, link netlink.Link, enable bool) error {
 	err := nlh.LinkSetHairpin(link, enable)
-	if err != nil && err != syscall.EINVAL {
-		// If error is not EINVAL something else went wrong, bail out right away
+	if err != nil {
 		return fmt.Errorf("unable to set hairpin mode on %s via netlink: %v",
 			link.Attrs().Name, err)
 	}
-
-	// Hairpin mode successfully set up
-	if err == nil {
-		return nil
-	}
-
-	// The netlink method failed with EINVAL which is probably because of an older
-	// kernel. Try one more time via the sysfs method.
-	path := filepath.Join("/sys/class/net", link.Attrs().Name, "brport/hairpin_mode")
-
-	var val []byte
-	if enable {
-		val = []byte{'1', '\n'}
-	} else {
-		val = []byte{'0', '\n'}
-	}
-
-	if err := os.WriteFile(path, val, 0644); err != nil {
-		return fmt.Errorf("unable to set hairpin mode on %s via sysfs: %v", link.Attrs().Name, err)
-	}
-
 	return nil
 }
 

libnetwork/drivers/overlay/ov_network.go

@@ -124,6 +124,8 @@ func setDefaultVlan() {
 	}
 
 	brName := os.Args[2]
+	// IFLA_BR_VLAN_DEFAULT_PVID was added in Linux v4.4 (see torvalds/linux@0f963b7), so we can't use netlink for
+	// setting this until Docker drops support for CentOS/RHEL 7 (kernel 3.10, eol date: 2024-06-30).
 	path := filepath.Join("/sys/class/net", brName, "bridge/default_pvid")
 	data := []byte{'0', '\n'}
 

libnetwork/osl/interface_linux.go

@@ -3,7 +3,6 @@ package osl
 import (
 	"fmt"
 	"net"
-	"regexp"
 	"sync"
 	"syscall"
 	"time"
@@ -418,30 +417,6 @@ func setInterfaceRoutes(nlh *netlink.Handle, iface netlink.Link, i *nwIface) err
 	return nil
 }
 
-// In older kernels (like the one in Centos 6.6 distro) sysctl does not have netns support. Therefore
-// we cannot gather the statistics from /sys/class/net/<dev>/statistics/<counter> files. Per-netns stats
-// are naturally found in /proc/net/dev in kernels which support netns (ifconfig relies on that).
-const (
-	base = "[ ]*%s:([ ]+[0-9]+){16}"
-)
-
-func scanInterfaceStats(data, ifName string, i *types.InterfaceStatistics) error {
-	var (
-		bktStr string
-		bkt    uint64
-	)
-
-	regex := fmt.Sprintf(base, ifName)
-	re := regexp.MustCompile(regex)
-	line := re.FindString(data)
-
-	_, err := fmt.Sscanf(line, "%s %d %d %d %d %d %d %d %d %d %d %d %d %d %d %d %d",
-		&bktStr, &i.RxBytes, &i.RxPackets, &i.RxErrors, &i.RxDropped, &bkt, &bkt, &bkt,
-		&bkt, &i.TxBytes, &i.TxPackets, &i.TxErrors, &i.TxDropped, &bkt, &bkt, &bkt, &bkt)
-
-	return err
-}
-
 func checkRouteConflict(nlh *netlink.Handle, address *net.IPNet, family int) error {
 	routes, err := nlh.RouteList(nil, family)
 	if err != nil {

libnetwork/osl/sandbox_linux_test.go

@@ -158,32 +158,6 @@ func verifyCleanup(t *testing.T, s Sandbox, wait bool) {
 	}
 }
 
-func TestScanStatistics(t *testing.T) {
-	data :=
-		"Inter-|   Receive                                                |  Transmit\n" +
-			"	face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed\n" +
-			"  eth0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0\n" +
-			" wlan0: 7787685   11141    0    0    0     0          0         0  1681390    7220    0    0    0     0       0          0\n" +
-			"    lo:  783782    1853    0    0    0     0          0         0   783782    1853    0    0    0     0       0          0\n" +
-			"lxcbr0:       0       0    0    0    0     0          0         0     9006      61    0    0    0     0       0          0\n"
-
-	i := &types.InterfaceStatistics{}
-
-	if err := scanInterfaceStats(data, "wlan0", i); err != nil {
-		t.Fatal(err)
-	}
-	if i.TxBytes != 1681390 || i.TxPackets != 7220 || i.RxBytes != 7787685 || i.RxPackets != 11141 {
-		t.Fatalf("Error scanning the statistics")
-	}
-
-	if err := scanInterfaceStats(data, "lxcbr0", i); err != nil {
-		t.Fatal(err)
-	}
-	if i.TxBytes != 9006 || i.TxPackets != 61 || i.RxBytes != 0 || i.RxPackets != 0 {
-		t.Fatalf("Error scanning the statistics")
-	}
-}
-
 func TestDisableIPv6DAD(t *testing.T) {
 	defer testutils.SetupTestOSContext(t)()