netstack/fdbased: add generic segmentation offload (GSO) support

The linux packet socket can handle GSO packets, so we can segment packets to
64K instead of the MTU which is usually 1500.

Here are numbers for the nginx-1m test:
runsc:		579330.01 [Kbytes/sec] received
runsc-gso:	1794121.66 [Kbytes/sec] received
runc:		2122139.06 [Kbytes/sec] received

and for tcp_benchmark:

$ tcp_benchmark  --duration 15   --ideal
[  4]  0.0-15.0 sec  86647 MBytes  48456 Mbits/sec

$ tcp_benchmark --client --duration 15   --ideal
[  4]  0.0-15.0 sec  2173 MBytes  1214 Mbits/sec

$ tcp_benchmark --client --duration 15   --ideal --gso 65536
[  4]  0.0-15.0 sec  19357 MBytes  10825 Mbits/sec

PiperOrigin-RevId: 240809103
Change-Id: I2637f104db28b5d4c64e1e766c610162a195775a

1 files changed, 32 insertions, 0 deletions

diff --git a/pkg/tcpip/link/fdbased/endpoint_unsafe.go b/pkg/tcpip/link/fdbased/endpoint_unsafe.go
new file mode 100644
index 000000000..36e7fe5a9
--- /dev/null
+++ b/pkg/tcpip/link/fdbased/endpoint_unsafe.go
@@ -0,0 +1,32 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build linux
+
+package fdbased
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+const virtioNetHdrSize = int(unsafe.Sizeof(virtioNetHdr{}))
+
+func vnetHdrToByteSlice(hdr *virtioNetHdr) (slice []byte) {
+	sh := (*reflect.SliceHeader)(unsafe.Pointer(&slice))
+	sh.Data = uintptr(unsafe.Pointer(hdr))
+	sh.Len = virtioNetHdrSize
+	sh.Cap = virtioNetHdrSize
+	return
+}