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, 29 insertions, 24 deletions

diff --git a/tun/tun_freebsd.go b/tun/tun_freebsd.go
index 42431aa..0783f74 100644
--- a/tun/tun_freebsd.go
+++ b/tun/tun_freebsd.go
@@ -333,45 +333,46 @@ func (tun *NativeTun) Events() <-chan Event {
 	return tun.events
 }
 
-func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
+func (tun *NativeTun) Read(buffs [][]byte, sizes []int, offset int) (int, error) {
 	select {
 	case err := <-tun.errors:
 		return 0, err
 	default:
-		buff := buff[offset-4:]
+		buff := buffs[0][offset-4:]
 		n, err := tun.tunFile.Read(buff[:])
 		if n < 4 {
 			return 0, err
 		}
-		return n - 4, err
+		sizes[0] = n - 4
+		return 1, err
 	}
 }
 
-func (tun *NativeTun) Write(buf []byte, offset int) (int, error) {
+func (tun *NativeTun) Write(buffs [][]byte, offset int) (int, error) {
 	if offset < 4 {
 		return 0, io.ErrShortBuffer
 	}
-	buf = buf[offset-4:]
-	if len(buf) < 5 {
-		return 0, io.ErrShortBuffer
-	}
-	buf[0] = 0x00
-	buf[1] = 0x00
-	buf[2] = 0x00
-	switch buf[4] >> 4 {
-	case 4:
-		buf[3] = unix.AF_INET
-	case 6:
-		buf[3] = unix.AF_INET6
-	default:
-		return 0, unix.EAFNOSUPPORT
+	for i, buf := range buffs {
+		buf = buf[offset-4:]
+		if len(buf) < 5 {
+			return i, io.ErrShortBuffer
+		}
+		buf[0] = 0x00
+		buf[1] = 0x00
+		buf[2] = 0x00
+		switch buf[4] >> 4 {
+		case 4:
+			buf[3] = unix.AF_INET
+		case 6:
+			buf[3] = unix.AF_INET6
+		default:
+			return i, unix.EAFNOSUPPORT
+		}
+		if _, err := tun.tunFile.Write(buf); err != nil {
+			return i, err
+		}
 	}
-	return tun.tunFile.Write(buf)
-}
-
-func (tun *NativeTun) Flush() error {
-	// TODO: can flushing be implemented by buffering and using sendmmsg?
-	return nil
+	return len(buffs), nil
 }
 
 func (tun *NativeTun) Close() error {
@@ -428,3 +429,7 @@ func (tun *NativeTun) MTU() (int, error) {
 	}
 	return int(*(*int32)(unsafe.Pointer(&ifr.MTU))), nil
 }
+
+func (tun *NativeTun) BatchSize() int {
+	return 1
+}