Merge release-20190806.1-143-ga8834fc (automated)

1 files changed, 118 insertions, 0 deletions

diff --git a/pkg/flipcall/futex_linux.go b/pkg/flipcall/futex_linux.go
new file mode 100755
index 000000000..b127a2bbb
--- /dev/null
+++ b/pkg/flipcall/futex_linux.go
@@ -0,0 +1,118 @@
+// 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.
+
+// +build linux
+
+package flipcall
+
+import (
+	"encoding/json"
+	"fmt"
+	"runtime"
+	"sync/atomic"
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+)
+
+func (ep *Endpoint) futexConnect(req *ctrlHandshakeRequest) (ctrlHandshakeResponse, error) {
+	var resp ctrlHandshakeResponse
+
+	// Write the handshake request.
+	w := ep.NewWriter()
+	if err := json.NewEncoder(w).Encode(req); err != nil {
+		return resp, fmt.Errorf("error writing handshake request: %v", err)
+	}
+	*ep.dataLen() = w.Len()
+
+	// Exchange control with the server.
+	if err := ep.futexSwitchToPeer(); err != nil {
+		return resp, err
+	}
+	if err := ep.futexSwitchFromPeer(); err != nil {
+		return resp, err
+	}
+
+	// Read the handshake response.
+	respLen := atomic.LoadUint32(ep.dataLen())
+	if respLen > ep.dataCap {
+		return resp, fmt.Errorf("invalid handshake response length %d (maximum %d)", respLen, ep.dataCap)
+	}
+	if err := json.NewDecoder(ep.NewReader(respLen)).Decode(&resp); err != nil {
+		return resp, fmt.Errorf("error reading handshake response: %v", err)
+	}
+
+	return resp, nil
+}
+
+func (ep *Endpoint) futexSwitchToPeer() error {
+	// Update connection state to indicate that the peer should be active.
+	if !atomic.CompareAndSwapUint32(ep.connState(), ep.activeState, ep.inactiveState) {
+		switch cs := atomic.LoadUint32(ep.connState()); cs {
+		case csShutdown:
+			return shutdownError{}
+		default:
+			return fmt.Errorf("unexpected connection state before FUTEX_WAKE: %v", cs)
+		}
+	}
+
+	// Wake the peer's Endpoint.futexSwitchFromPeer().
+	if err := ep.futexWakeConnState(1); err != nil {
+		return fmt.Errorf("failed to FUTEX_WAKE peer Endpoint: %v", err)
+	}
+	return nil
+}
+
+func (ep *Endpoint) futexSwitchFromPeer() error {
+	for {
+		switch cs := atomic.LoadUint32(ep.connState()); cs {
+		case ep.activeState:
+			return nil
+		case ep.inactiveState:
+			if ep.isShutdownLocally() {
+				return shutdownError{}
+			}
+			if err := ep.futexWaitConnState(ep.inactiveState); err != nil {
+				return fmt.Errorf("failed to FUTEX_WAIT for peer Endpoint: %v", err)
+			}
+			continue
+		case csShutdown:
+			return shutdownError{}
+		default:
+			return fmt.Errorf("unexpected connection state before FUTEX_WAIT: %v", cs)
+		}
+	}
+}
+
+func (ep *Endpoint) futexWakeConnState(numThreads int32) error {
+	if _, _, e := syscall.RawSyscall(syscall.SYS_FUTEX, ep.packet, linux.FUTEX_WAKE, uintptr(numThreads)); e != 0 {
+		return e
+	}
+	return nil
+}
+
+func (ep *Endpoint) futexWaitConnState(curState uint32) error {
+	_, _, e := syscall.Syscall6(syscall.SYS_FUTEX, ep.packet, linux.FUTEX_WAIT, uintptr(curState), 0, 0, 0)
+	if e != 0 && e != syscall.EAGAIN && e != syscall.EINTR {
+		return e
+	}
+	return nil
+}
+
+func yieldThread() {
+	syscall.Syscall(syscall.SYS_SCHED_YIELD, 0, 0, 0)
+	// The thread we're trying to yield to may be waiting for a Go runtime P.
+	// runtime.Gosched() will hand off ours if necessary.
+	runtime.Gosched()
+}