[lisa] lisafs package POC.

This change mainly aims to define the semantics of communication for the LISAFS
(LInux SAndbox Filesystem) protocol. This protocol aims to replace 9P and
intends to bring some performance benefits with it.

Some of the notable differences from the p9 package are:
- Now the server implementations own the handlers.
- As a result, there is no verbose interface like `p9.File` that all servers
  need to implement. Different implementations can extend their File
  implementations to varying degrees without imposing those extensions to other
  server implementations that might not have anything to do with those features.
- If a server implementation adds a new RPC message, other implementations are
  not compelled to support it.

I wrote a benchmark `BenchmarkSendRecv` in connection_test.go which competes
with p9's `BenchmarkSendRecvChannel`. Running these on an AMD Milan machine
shows that lisafs is **45%** faster.

**With 9P**
goos: linux
goarch: amd64
pkg: gvisor/pkg/p9/p9
cpu: AMD EPYC 7B13 64-Core Processor
BenchmarkSendRecvLegacy-256     82830     14053 ns/op     633 B/op     23 allocs/op
BenchmarkSendRecvChannel-256     776971     1551 ns/op     184 B/op     6 allocs/op

**With lisafs**
goos: linux
goarch: amd64
pkg: pkg/lisafs/connection_test
cpu: AMD EPYC 7B13 64-Core Processor
BenchmarkSendRecv-256     1399610     853.5 ns/op     48 B/op     2 allocs/op

Fixes #5464

PiperOrigin-RevId: 397803163

1 files changed, 110 insertions, 0 deletions

diff --git a/pkg/lisafs/sample_message.go b/pkg/lisafs/sample_message.go
new file mode 100644
index 000000000..3868dfa08
--- /dev/null
+++ b/pkg/lisafs/sample_message.go
@@ -0,0 +1,110 @@
+// Copyright 2021 The gVisor Authors.
+//
+// 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.
+
+package lisafs
+
+import (
+	"math/rand"
+
+	"gvisor.dev/gvisor/pkg/marshal/primitive"
+)
+
+// MsgSimple is a sample packed struct which can be used to test message passing.
+//
+// +marshal slice:Msg1Slice
+type MsgSimple struct {
+	A uint16
+	B uint16
+	C uint32
+	D uint64
+}
+
+// Randomize randomizes the contents of m.
+func (m *MsgSimple) Randomize() {
+	m.A = uint16(rand.Uint32())
+	m.B = uint16(rand.Uint32())
+	m.C = rand.Uint32()
+	m.D = rand.Uint64()
+}
+
+// MsgDynamic is a sample dynamic struct which can be used to test message passing.
+//
+// +marshal dynamic
+type MsgDynamic struct {
+	N   primitive.Uint32
+	Arr []MsgSimple
+}
+
+// SizeBytes implements marshal.Marshallable.SizeBytes.
+func (m *MsgDynamic) SizeBytes() int {
+	return m.N.SizeBytes() +
+		(int(m.N) * (*MsgSimple)(nil).SizeBytes())
+}
+
+// MarshalBytes implements marshal.Marshallable.MarshalBytes.
+func (m *MsgDynamic) MarshalBytes(dst []byte) {
+	m.N.MarshalUnsafe(dst)
+	dst = dst[m.N.SizeBytes():]
+	MarshalUnsafeMsg1Slice(m.Arr, dst)
+}
+
+// UnmarshalBytes implements marshal.Marshallable.UnmarshalBytes.
+func (m *MsgDynamic) UnmarshalBytes(src []byte) {
+	m.N.UnmarshalUnsafe(src)
+	src = src[m.N.SizeBytes():]
+	m.Arr = make([]MsgSimple, m.N)
+	UnmarshalUnsafeMsg1Slice(m.Arr, src)
+}
+
+// Randomize randomizes the contents of m.
+func (m *MsgDynamic) Randomize(arrLen int) {
+	m.N = primitive.Uint32(arrLen)
+	m.Arr = make([]MsgSimple, arrLen)
+	for i := 0; i < arrLen; i++ {
+		m.Arr[i].Randomize()
+	}
+}
+
+// P9Version mimics p9.TVersion and p9.Rversion.
+//
+// +marshal dynamic
+type P9Version struct {
+	MSize   primitive.Uint32
+	Version string
+}
+
+// SizeBytes implements marshal.Marshallable.SizeBytes.
+func (v *P9Version) SizeBytes() int {
+	return (*primitive.Uint32)(nil).SizeBytes() + (*primitive.Uint16)(nil).SizeBytes() + len(v.Version)
+}
+
+// MarshalBytes implements marshal.Marshallable.MarshalBytes.
+func (v *P9Version) MarshalBytes(dst []byte) {
+	v.MSize.MarshalUnsafe(dst)
+	dst = dst[v.MSize.SizeBytes():]
+	versionLen := primitive.Uint16(len(v.Version))
+	versionLen.MarshalUnsafe(dst)
+	dst = dst[versionLen.SizeBytes():]
+	copy(dst, v.Version)
+}
+
+// UnmarshalBytes implements marshal.Marshallable.UnmarshalBytes.
+func (v *P9Version) UnmarshalBytes(src []byte) {
+	v.MSize.UnmarshalUnsafe(src)
+	src = src[v.MSize.SizeBytes():]
+	var versionLen primitive.Uint16
+	versionLen.UnmarshalUnsafe(src)
+	src = src[versionLen.SizeBytes():]
+	v.Version = string(src[:versionLen])
+}