the definitive tun offloads branch (#1704)

udp/conn.go

@@ -8,16 +8,41 @@ import (
 
 const MTU = 9001
 
+// MaxWriteBatch is the largest batch any Conn.WriteBatch implementation is
+// required to accept. Callers SHOULD NOT pass more than this per call; Linux
+// backends preallocate sendmmsg scratch sized to this value, so exceeding it
+// only costs additional sendmmsg chunks within a single WriteBatch call.
+const MaxWriteBatch = 128
+
 type EncReader func(
 	addr netip.AddrPort,
 	payload []byte,
 )
 
+type Settings struct {
+	Listen   netip.AddrPort
+	Multi    bool
+	Batch    int
+	Offloads bool
+}
+
 type Conn interface {
 	Rebind() error
 	LocalAddr() (netip.AddrPort, error)
-	ListenOut(r EncReader) error
+	// ListenOut invokes r for each received packet.
+	// On batch-capable backends (recvmmsg), flush is called after each batch is fully delivered.
+	// Callers use it to flush per-batch accumulators such as TUN write coalescers.
+	// Single-packet backends call flush after each packet. flush must not be nil.
+	ListenOut(r EncReader, flush func()) error
 	WriteTo(b []byte, addr netip.AddrPort) error
+	// WriteBatch sends a contiguous batch of packets, each with its own
+	// destination. bufs and addrs must have the same length. Linux uses
+	// sendmmsg(2) for a single syscall.
+	//
+	// Returns the number of packets successfully written. A destination the kernel rejects costs only
+	// its own packet, so a short count means some peers were undeliverable, not that the batch failed.
+	// Not safe for concurrent use on the same Conn.
+	WriteBatch(bufs [][]byte, addrs []netip.AddrPort) (int, error)
 	ReloadConfig(c *config.C)
 	SupportsMultipleReaders() bool
 	Close() error
@@ -31,7 +56,7 @@ func (NoopConn) Rebind() error {
 func (NoopConn) LocalAddr() (netip.AddrPort, error) {
 	return netip.AddrPort{}, nil
 }
-func (NoopConn) ListenOut(_ EncReader) error {
+func (NoopConn) ListenOut(_ EncReader, _ func()) error {
 	return nil
 }
 func (NoopConn) SupportsMultipleReaders() bool {
@@ -40,6 +65,9 @@ func (NoopConn) SupportsMultipleReaders() bool {
 func (NoopConn) WriteTo(_ []byte, _ netip.AddrPort) error {
 	return nil
 }
+func (NoopConn) WriteBatch(bufs [][]byte, _ []netip.AddrPort) (int, error) {
+	return len(bufs), nil
+}
 func (NoopConn) ReloadConfig(_ *config.C) {
 	return
 }