link: netkit: Add support for Headroom and Tailroom attributes.

IFLA_NETKIT_HEADROOM and IFLA_NETKIT_TAILROOM attributes were added to upstream kernel 6.14, allowing Netkit devices to be configured with appropriate headroom/tailroom space to accommodate additional headers, packet length changes and so forth. Signed-off-by: Alasdair McWilliam <alasdair.mcwilliam@isovalent.com>
2025-09-26 20:01:13 +08:00 · 2025-08-21 11:00:57 +01:00
parent 349c84c717
commit cf66e1d224
4 changed files with 112 additions and 5 deletions
--- a/link.go
+++ b/link.go
@@ -410,6 +410,8 @@ type Netkit struct {
 	PeerPolicy    NetkitPolicy
 	Scrub         NetkitScrub
 	PeerScrub     NetkitScrub
+	Headroom      uint16
+	Tailroom      uint16
 	supportsScrub bool
 	isPrimary     bool
 	peerLinkAttrs LinkAttrs
--- a/link_linux.go
+++ b/link_linux.go
@@ -2802,6 +2802,15 @@ func addNetkitAttrs(nk *Netkit, linkInfo *nl.RtAttr, flag int) error {
 	data.AddRtAttr(nl.IFLA_NETKIT_SCRUB, nl.Uint32Attr(uint32(nk.Scrub)))
 	data.AddRtAttr(nl.IFLA_NETKIT_PEER_SCRUB, nl.Uint32Attr(uint32(nk.PeerScrub)))

+	// Any headroom or tailroom set on the primary device attributes will result in
+	// the kernel carrying them over into the peer device attributes for us.
+	if nk.Headroom > 0 {
+		data.AddRtAttr(nl.IFLA_NETKIT_HEADROOM, nl.Uint16Attr(nk.Headroom))
+	}
+	if nk.Tailroom > 0 {
+		data.AddRtAttr(nl.IFLA_NETKIT_TAILROOM, nl.Uint16Attr(nk.Tailroom))
+	}
+
 	if (flag & unix.NLM_F_EXCL) == 0 {
 		// Modifying peer link attributes will not take effect
 		return nil
@@ -2870,6 +2879,10 @@ func parseNetkitData(link Link, data []syscall.NetlinkRouteAttr) {
 		case nl.IFLA_NETKIT_PEER_SCRUB:
 			netkit.supportsScrub = true
 			netkit.PeerScrub = NetkitScrub(native.Uint32(datum.Value[0:4]))
+		case nl.IFLA_NETKIT_HEADROOM:
+			netkit.Headroom = native.Uint16(datum.Value[0:2])
+		case nl.IFLA_NETKIT_TAILROOM:
+			netkit.Tailroom = native.Uint16(datum.Value[0:2])
 		}
 	}
 }
--- a/link_test.go
+++ b/link_test.go
@@ -23,10 +23,12 @@ import (
 )

 const (
-	testTxQLen    int = 100
-	defaultTxQLen int = 1000
-	testTxQueues  int = 4
-	testRxQueues  int = 8
+	testTxQLen    int    = 100
+	defaultTxQLen int    = 1000
+	testTxQueues  int    = 4
+	testRxQueues  int    = 8
+	testHeadroom  uint16 = 32
+	testTailroom  uint16 = 64
 )

 func testLinkAddDel(t *testing.T, link Link) {
@@ -87,6 +89,12 @@ func testLinkAddDel(t *testing.T, link Link) {
 			if resultPrimary.SupportsScrub() && resultPrimary.PeerScrub != inputPrimary.PeerScrub {
 				t.Fatalf("Peer Scrub is %d, should be %d", int(resultPrimary.PeerScrub), int(inputPrimary.PeerScrub))
 			}
+			if resultPrimary.Headroom != inputPrimary.Headroom {
+				t.Fatalf("Headroom is %d, should be %d", resultPrimary.Headroom, inputPrimary.Headroom)
+			}
+			if resultPrimary.Tailroom != inputPrimary.Tailroom {
+				t.Fatalf("Tailroom is %d, should be %d", resultPrimary.Tailroom, inputPrimary.Tailroom)
+			}
 			if inputPrimary.Mode == NETKIT_MODE_L2 && inputPrimary.HardwareAddr != nil {
 				if inputPrimary.HardwareAddr.String() != resultPrimary.HardwareAddr.String() {
 					t.Fatalf("Hardware address is %s, should be %s", resultPrimary.HardwareAddr.String(), inputPrimary.HardwareAddr.String())
@@ -123,6 +131,12 @@ func testLinkAddDel(t *testing.T, link Link) {
 				if resultPrimary.Scrub != resultPeer.PeerScrub {
 					t.Fatalf("PeerScrub from peer is %d, should be %d", int(resultPeer.PeerScrub), int(resultPrimary.Scrub))
 				}
+				if resultPrimary.Headroom != resultPeer.Headroom {
+					t.Fatalf("Headroom from peer is %d, should be %d", resultPeer.Headroom, resultPeer.Headroom)
+				}
+				if resultPrimary.Tailroom != resultPeer.Tailroom {
+					t.Fatalf("Tailroom from peer is %d, should be %d", resultPeer.Tailroom, resultPeer.Tailroom)
+				}
 				if inputPrimary.Mode == NETKIT_MODE_L2 && inputPrimary.peerLinkAttrs.HardwareAddr != nil {
 					if inputPrimary.peerLinkAttrs.HardwareAddr.String() != resultPeer.HardwareAddr.String() {
 						t.Fatalf("Peer hardware address is %s, should be %s", resultPeer.HardwareAddr.String(), inputPrimary.peerLinkAttrs.HardwareAddr.String())
@@ -1261,6 +1275,82 @@ func TestLinkAddDelNetkit(t *testing.T) {
 	testLinkAddDel(t, netkit)
 }

+func TestLinkAddDelNetkitWithHeadroom(t *testing.T) {
+	minKernelRequired(t, 6, 14)
+	tearDown := setUpNetlinkTest(t)
+	defer tearDown()
+
+	netkit := &Netkit{
+		LinkAttrs: LinkAttrs{
+			Name:         "foo",
+			HardwareAddr: net.HardwareAddr{0x00, 0x11, 0x22, 0x33, 0x44, 0x55},
+		},
+		Mode:       NETKIT_MODE_L2,
+		Policy:     NETKIT_POLICY_FORWARD,
+		PeerPolicy: NETKIT_POLICY_BLACKHOLE,
+		Scrub:      NETKIT_SCRUB_DEFAULT,
+		PeerScrub:  NETKIT_SCRUB_NONE,
+		Headroom:   testHeadroom,
+	}
+	peerAttr := &LinkAttrs{
+		Name:         "bar",
+		HardwareAddr: net.HardwareAddr{0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB},
+	}
+	netkit.SetPeerAttrs(peerAttr)
+	testLinkAddDel(t, netkit)
+}
+
+func TestLinkAddDelNetkitWithTailroom(t *testing.T) {
+	minKernelRequired(t, 6, 14)
+	tearDown := setUpNetlinkTest(t)
+	defer tearDown()
+
+	netkit := &Netkit{
+		LinkAttrs: LinkAttrs{
+			Name:         "foo",
+			HardwareAddr: net.HardwareAddr{0x00, 0x11, 0x22, 0x33, 0x44, 0x55},
+		},
+		Mode:       NETKIT_MODE_L2,
+		Policy:     NETKIT_POLICY_FORWARD,
+		PeerPolicy: NETKIT_POLICY_BLACKHOLE,
+		Scrub:      NETKIT_SCRUB_DEFAULT,
+		PeerScrub:  NETKIT_SCRUB_NONE,
+		Tailroom:   testTailroom,
+	}
+	peerAttr := &LinkAttrs{
+		Name:         "bar",
+		HardwareAddr: net.HardwareAddr{0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB},
+	}
+	netkit.SetPeerAttrs(peerAttr)
+	testLinkAddDel(t, netkit)
+}
+
+func TestLinkAddDelNetkitWithHeadAndTailroom(t *testing.T) {
+	minKernelRequired(t, 6, 14)
+	tearDown := setUpNetlinkTest(t)
+	defer tearDown()
+
+	netkit := &Netkit{
+		LinkAttrs: LinkAttrs{
+			Name:         "foo",
+			HardwareAddr: net.HardwareAddr{0x00, 0x11, 0x22, 0x33, 0x44, 0x55},
+		},
+		Mode:       NETKIT_MODE_L2,
+		Policy:     NETKIT_POLICY_FORWARD,
+		PeerPolicy: NETKIT_POLICY_BLACKHOLE,
+		Scrub:      NETKIT_SCRUB_DEFAULT,
+		PeerScrub:  NETKIT_SCRUB_NONE,
+		Headroom:   testHeadroom,
+		Tailroom:   testTailroom,
+	}
+	peerAttr := &LinkAttrs{
+		Name:         "bar",
+		HardwareAddr: net.HardwareAddr{0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB},
+	}
+	netkit.SetPeerAttrs(peerAttr)
+	testLinkAddDel(t, netkit)
+}
+
 func TestLinkAddDelVeth(t *testing.T) {
 	t.Cleanup(setUpNetlinkTest(t))

--- a/nl/link_linux.go
+++ b/nl/link_linux.go
@@ -54,7 +54,9 @@ const (
 	IFLA_NETKIT_MODE
 	IFLA_NETKIT_SCRUB
 	IFLA_NETKIT_PEER_SCRUB
-	IFLA_NETKIT_MAX = IFLA_NETKIT_MODE
+	IFLA_NETKIT_HEADROOM
+	IFLA_NETKIT_TAILROOM
+	IFLA_NETKIT_MAX = IFLA_NETKIT_TAILROOM
 )

 const (