Fix usages of readmsg_x

internal/fdbased_darwin/endpoint.go

@@ -74,12 +74,29 @@ const (
 	// dispatch options but the one that is supported by all underlying FD
 	// types.
 	Readv PacketDispatchMode = iota
+	// RecvMMsg enables use of recvmmsg() syscall instead of readv() to
+	// read inbound packets. This reduces # of syscalls needed to process
+	// packets.
+	//
+	// NOTE: recvmmsg() is only supported for sockets, so if the underlying
+	// FD is not a socket then the code will still fall back to the readv()
+	// path.
+	RecvMMsg
+	// PacketMMap enables use of PACKET_RX_RING to receive packets from the
+	// NIC. PacketMMap requires that the underlying FD be an AF_PACKET. The
+	// primary use-case for this is runsc which uses an AF_PACKET FD to
+	// receive packets from the veth device.
+	PacketMMap
 )
 
 func (p PacketDispatchMode) String() string {
 	switch p {
 	case Readv:
 		return "Readv"
+	case RecvMMsg:
+		return "RecvMMsg"
+	case PacketMMap:
+		return "PacketMMap"
 	default:
 		return fmt.Sprintf("unknown packet dispatch mode '%d'", p)
 	}
@@ -283,14 +300,6 @@ func New(opts *Options) (stack.LinkEndpoint, error) {
 	return e, nil
 }
 
-func isSocketFD(fd int) (bool, error) {
-	var stat unix.Stat_t
-	if err := unix.Fstat(fd, &stat); err != nil {
-		return false, fmt.Errorf("unix.Fstat(%v,...) failed: %v", fd, err)
-	}
-	return (stat.Mode & unix.S_IFSOCK) == unix.S_IFSOCK, nil
-}
-
 // Attach launches the goroutine that reads packets from the file descriptor and
 // dispatches them via the provided dispatcher. If one is already attached,
 // then nothing happens.