conn, device, tun: implement vectorized I/O plumbing

Accept packet vectors for reading and writing in the tun.Device and
conn.Bind interfaces, so that the internal plumbing between these
interfaces now passes a vector of packets. Vectors move untouched
between these interfaces, i.e. if 128 packets are received from
conn.Bind.Read(), 128 packets are passed to tun.Device.Write(). There is
no internal buffering.

Currently, existing implementations are only adjusted to have vectors
of length one. Subsequent patches will improve that.

Also, as a related fixup, use the unix and windows packages rather than
the syscall package when possible.

Co-authored-by: James Tucker <james@tailscale.com>
Signed-off-by: James Tucker <james@tailscale.com>
Signed-off-by: Jordan Whited <jordan@tailscale.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 28 insertions, 9 deletions

diff --git a/conn/bind_std.go b/conn/bind_std.go
index ae07aac..98fe23c 100644
--- a/conn/bind_std.go
+++ b/conn/bind_std.go
@@ -128,6 +128,10 @@ again:
 	return fns, uint16(port), nil
 }
 
+func (bind *StdNetBind) BatchSize() int {
+	return 1
+}
+
 func (bind *StdNetBind) Close() error {
 	bind.mu.Lock()
 	defer bind.mu.Unlock()
@@ -150,20 +154,30 @@ func (bind *StdNetBind) Close() error {
 }
 
 func (*StdNetBind) makeReceiveIPv4(conn *net.UDPConn) ReceiveFunc {
-	return func(buff []byte) (int, Endpoint, error) {
-		n, endpoint, err := conn.ReadFromUDPAddrPort(buff)
-		return n, asEndpoint(endpoint), err
+	return func(buffs [][]byte, sizes []int, eps []Endpoint) (n int, err error) {
+		size, endpoint, err := conn.ReadFromUDPAddrPort(buffs[0])
+		if err == nil {
+			sizes[0] = size
+			eps[0] = asEndpoint(endpoint)
+			return 1, nil
+		}
+		return 0, err
 	}
 }
 
 func (*StdNetBind) makeReceiveIPv6(conn *net.UDPConn) ReceiveFunc {
-	return func(buff []byte) (int, Endpoint, error) {
-		n, endpoint, err := conn.ReadFromUDPAddrPort(buff)
-		return n, asEndpoint(endpoint), err
+	return func(buffs [][]byte, sizes []int, eps []Endpoint) (n int, err error) {
+		size, endpoint, err := conn.ReadFromUDPAddrPort(buffs[0])
+		if err == nil {
+			sizes[0] = size
+			eps[0] = asEndpoint(endpoint)
+			return 1, nil
+		}
+		return 0, err
 	}
 }
 
-func (bind *StdNetBind) Send(buff []byte, endpoint Endpoint) error {
+func (bind *StdNetBind) Send(buffs [][]byte, endpoint Endpoint) error {
 	var err error
 	nend, ok := endpoint.(StdNetEndpoint)
 	if !ok {
@@ -186,8 +200,13 @@ func (bind *StdNetBind) Send(buff []byte, endpoint Endpoint) error {
 	if conn == nil {
 		return syscall.EAFNOSUPPORT
 	}
-	_, err = conn.WriteToUDPAddrPort(buff, addrPort)
-	return err
+	for _, buff := range buffs {
+		_, err = conn.WriteToUDPAddrPort(buff, addrPort)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 // endpointPool contains a re-usable set of mapping from netip.AddrPort to Endpoint.