Experimenting

overlay/tun_freebsd.go

@@ -158,74 +158,43 @@ func (t *tun) blockOnWrite() error {
 }
 
 func (t *tun) Read(to []byte) (int, error) {
-	// first 4 bytes is protocol family, in network byte order
-	var head [4]byte
-	iovecs := [2]syscall.Iovec{
-		{&head[0], 4},
-		{&to[0], uint64(len(to))},
-	}
 	for {
-		n, _, errno := syscall.Syscall(syscall.SYS_READV, uintptr(t.fd), uintptr(unsafe.Pointer(&iovecs[0])), 2)
-		if errno == 0 {
-			bytesRead := int(n)
-			if bytesRead < 4 {
-				return 0, nil
-			}
-			return bytesRead - 4, nil
+		n, err := unix.Read(t.fd, to)
+		if err == nil {
+			return n, nil
 		}
-		switch errno {
+		switch err {
 		case unix.EAGAIN:
-			if err := t.blockOnRead(); err != nil {
-				return 0, err
+			if berr := t.blockOnRead(); berr != nil {
+				return 0, berr
 			}
 		case unix.EINTR:
 			// retry
 		case unix.EBADF:
 			return 0, os.ErrClosed
 		default:
-			return 0, errno
+			return 0, err
 		}
 	}
 }
 
-// Write is only valid for single threaded use
 func (t *tun) Write(from []byte) (int, error) {
-	if len(from) <= 1 {
-		return 0, syscall.EIO
-	}
-
-	ipVer := from[0] >> 4
-	var head [4]byte
-	// first 4 bytes is protocol family, in network byte order
-	switch ipVer {
-	case 4:
-		head[3] = syscall.AF_INET
-	case 6:
-		head[3] = syscall.AF_INET6
-	default:
-		return 0, fmt.Errorf("unable to determine IP version from packet")
-	}
-
-	iovecs := [2]syscall.Iovec{
-		{&head[0], 4},
-		{&from[0], uint64(len(from))},
-	}
 	for {
-		n, _, errno := syscall.Syscall(syscall.SYS_WRITEV, uintptr(t.fd), uintptr(unsafe.Pointer(&iovecs[0])), 2)
-		if errno == 0 {
-			return int(n) - 4, nil
+		n, err := unix.Write(t.fd, from)
+		if err == nil {
+			return n, nil
 		}
-		switch errno {
+		switch err {
 		case unix.EAGAIN:
-			if err := t.blockOnWrite(); err != nil {
-				return 0, err
+			if berr := t.blockOnWrite(); berr != nil {
+				return 0, berr
 			}
 		case unix.EINTR:
 			// retry
 		case unix.EBADF:
 			return 0, os.ErrClosed
 		default:
-			return 0, errno
+			return 0, err
 		}
 	}
 }
@@ -732,3 +701,7 @@ func getLinkAddr(name string) (*netroute.LinkAddr, error) {
 
 	return nil, nil
 }
+
+// TunPrefixLen reports the 4-byte BSD AF_INET / AF_INET6 protocol-family
+// marker the kernel prepends on read and expects on write.
+func (t *tun) TunPrefixLen() int { return 4 }