works well

interface.go

@@ -8,6 +8,7 @@ import (
 	"net/netip"
 	"os"
 	"runtime"
+	"strings"
 	"sync/atomic"
 	"time"
 
@@ -399,6 +400,12 @@ func (f *Interface) listenInBatchLocked(raw io.ReadWriteCloser, reader overlay.B
 				return
 			}
 
+			if isVirtioHeadroomError(err) {
+				f.l.WithError(err).Warn("Batch reader fell back due to tun headroom issue")
+				f.listenInLegacyLocked(raw, i)
+				return
+			}
+
 			f.l.WithError(err).Error("Error while reading outbound packet batch")
 			os.Exit(2)
 		}
@@ -549,6 +556,7 @@ func (f *Interface) runTunWriteQueue(i int) {
 	if writer == nil {
 		return
 	}
+	requiredHeadroom := writer.BatchHeadroom()
 
 	batchCap := f.batches.batchSizeHint()
 	if batchCap <= 0 {
@@ -563,15 +571,27 @@ func (f *Interface) runTunWriteQueue(i int) {
 		if len(pending) == 0 {
 			return
 		}
-		if _, err := writer.WriteBatch(pending); err != nil {
-			f.l.WithError(err).
-				WithField("queue", i).
-				WithField("reason", reason).
-				Warn("Failed to write tun batch")
-		}
+		valid := pending[:0]
 		for idx := range pending {
+			if !f.ensurePacketHeadroom(&pending[idx], requiredHeadroom, i, reason) {
+				pending[idx] = nil
+				continue
+			}
 			if pending[idx] != nil {
-				pending[idx].Release()
+				valid = append(valid, pending[idx])
+			}
+		}
+		if len(valid) > 0 {
+			if _, err := writer.WriteBatch(valid); err != nil {
+				f.l.WithError(err).
+					WithField("queue", i).
+					WithField("reason", reason).
+					Warn("Failed to write tun batch")
+				for _, pkt := range valid {
+					if pkt != nil {
+						f.writePacketToTun(i, pkt)
+					}
+				}
 			}
 		}
 		pending = pending[:0]
@@ -605,7 +625,9 @@ func (f *Interface) runTunWriteQueue(i int) {
 			if pkt == nil {
 				continue
 			}
-			pending = append(pending, pkt)
+			if f.ensurePacketHeadroom(&pkt, requiredHeadroom, i, "queue") {
+				pending = append(pending, pkt)
+			}
 			if len(pending) >= cap(pending) {
 				flush("cap", false)
 				continue
@@ -811,6 +833,40 @@ func (f *Interface) writePacketToTun(q int, pkt *overlay.Packet) {
 	pkt.Release()
 }
 
+func (f *Interface) clonePacketWithHeadroom(pkt *overlay.Packet, required int) *overlay.Packet {
+	if pkt == nil {
+		return nil
+	}
+	payload := pkt.Payload()[:pkt.Len]
+	if len(payload) == 0 && required <= 0 {
+		return pkt
+	}
+
+	pool := f.batches.Pool()
+	if pool != nil {
+		if clone := pool.Get(); clone != nil {
+			if len(clone.Payload()) >= len(payload) {
+				clone.Len = copy(clone.Payload(), payload)
+				pkt.Release()
+				return clone
+			}
+			clone.Release()
+		}
+	}
+
+	if required < 0 {
+		required = 0
+	}
+	buf := make([]byte, required+len(payload))
+	n := copy(buf[required:], payload)
+	pkt.Release()
+	return &overlay.Packet{
+		Buf:    buf,
+		Offset: required,
+		Len:    n,
+	}
+}
+
 func (f *Interface) observeUDPQueueLen(i int) {
 	if f.batchUDPQueueGauge == nil {
 		return
@@ -832,6 +888,34 @@ func (f *Interface) currentBatchFlushInterval() time.Duration {
 	return 0
 }
 
+func (f *Interface) ensurePacketHeadroom(pkt **overlay.Packet, required int, queue int, reason string) bool {
+	p := *pkt
+	if p == nil {
+		return false
+	}
+	if required <= 0 || p.Offset >= required {
+		return true
+	}
+	clone := f.clonePacketWithHeadroom(p, required)
+	if clone == nil {
+		f.l.WithFields(logrus.Fields{
+			"queue":  queue,
+			"reason": reason,
+		}).Warn("dropping packet lacking tun headroom")
+		return false
+	}
+	*pkt = clone
+	return true
+}
+
+func isVirtioHeadroomError(err error) bool {
+	if err == nil {
+		return false
+	}
+	msg := err.Error()
+	return strings.Contains(msg, "headroom") || strings.Contains(msg, "virtio")
+}
+
 func (f *Interface) effectiveGSOMaxSegments() int {
 	max := f.gsoMaxSegments
 	if max <= 0 {