Flipcall refinements.

Note that some of these changes affect the protocol in
backward-incompatible ways.

- Replace use of "initially-active" and "initially-inactive" with
"client" and "server" respectively for clarity.

- Fix a race condition involving Endpoint.Shutdown() by repeatedly
invoking FUTEX_WAKE until it is confirmed that no local thread is
blocked in FUTEX_WAIT.

- Drop flipcall.ControlMode.

PiperOrigin-RevId: 260981382

1 files changed, 69 insertions, 0 deletions

diff --git a/pkg/flipcall/flipcall_unsafe.go b/pkg/flipcall/flipcall_unsafe.go
new file mode 100644
index 000000000..7c8977893
--- /dev/null
+++ b/pkg/flipcall/flipcall_unsafe.go
@@ -0,0 +1,69 @@
+// Copyright 2019 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 flipcall
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+// Packets consist of an 8-byte header followed by an arbitrarily-sized
+// datagram. The header consists of:
+//
+// - A 4-byte native-endian connection state.
+//
+// - A 4-byte native-endian datagram length in bytes.
+const (
+	sizeofUint32 = unsafe.Sizeof(uint32(0))
+
+	// PacketHeaderBytes is the size of a flipcall packet header in bytes. The
+	// maximum datagram size supported by a flipcall connection is equal to the
+	// length of the packet window minus PacketHeaderBytes.
+	//
+	// PacketHeaderBytes is exported to support its use in constant
+	// expressions. Non-constant expressions may prefer to use
+	// PacketWindowLengthForDataCap().
+	PacketHeaderBytes = 2 * sizeofUint32
+)
+
+func (ep *Endpoint) connState() *uint32 {
+	return (*uint32)((unsafe.Pointer)(ep.packet))
+}
+
+func (ep *Endpoint) dataLen() *uint32 {
+	return (*uint32)((unsafe.Pointer)(ep.packet + sizeofUint32))
+}
+
+// Data returns the datagram part of ep's packet window as a byte slice.
+//
+// Note that the packet window is shared with the potentially-untrusted peer
+// Endpoint, which may concurrently mutate the contents of the packet window.
+// Thus:
+//
+// - Readers must not assume that two reads of the same byte in Data() will
+// return the same result. In other words, readers should read any given byte
+// in Data() at most once.
+//
+// - Writers must not assume that they will read back the same data that they
+// have written. In other words, writers should avoid reading from Data() at
+// all.
+func (ep *Endpoint) Data() []byte {
+	var bs []byte
+	bsReflect := (*reflect.SliceHeader)((unsafe.Pointer)(&bs))
+	bsReflect.Data = ep.packet + PacketHeaderBytes
+	bsReflect.Len = int(ep.dataCap)
+	bsReflect.Cap = int(ep.dataCap)
+	return bs
+}