conn, device, tun: implement vectorized I/O on Linux

Implement TCP offloading via TSO and GRO for the Linux tun.Device, which
is made possible by virtio extensions in the kernel's TUN driver.

Delete conn.LinuxSocketEndpoint in favor of a collapsed conn.StdNetBind.
conn.StdNetBind makes use of recvmmsg() and sendmmsg() on Linux. All
platforms now fall under conn.StdNetBind, except for Windows, which
remains in conn.WinRingBind, which still needs to be adjusted to handle
multiple packets.

Also refactor sticky sockets support to eventually be applicable on
platforms other than just Linux. However Linux remains the sole platform
that fully implements it for now.

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, 5 insertions, 5 deletions

diff --git a/conn/mark_unix.go b/conn/mark_unix.go
index 5566b28..d9e46ee 100644
--- a/conn/mark_unix.go
+++ b/conn/mark_unix.go
@@ -26,13 +26,13 @@ func init() {
 	}
 }
 
-func (bind *StdNetBind) SetMark(mark uint32) error {
+func (s *StdNetBind) SetMark(mark uint32) error {
 	var operr error
 	if fwmarkIoctl == 0 {
 		return nil
 	}
-	if bind.ipv4 != nil {
-		fd, err := bind.ipv4.SyscallConn()
+	if s.ipv4 != nil {
+		fd, err := s.ipv4.SyscallConn()
 		if err != nil {
 			return err
 		}
@@ -46,8 +46,8 @@ func (bind *StdNetBind) SetMark(mark uint32) error {
 			return err
 		}
 	}
-	if bind.ipv6 != nil {
-		fd, err := bind.ipv6.SyscallConn()
+	if s.ipv6 != nil {
+		fd, err := s.ipv6.SyscallConn()
 		if err != nil {
 			return err
 		}