112 lines
3.3 KiB
Go
112 lines
3.3 KiB
Go
// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// +build linux
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package flipcall
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import (
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"encoding/json"
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"fmt"
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"runtime"
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"sync/atomic"
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"syscall"
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"gvisor.dev/gvisor/pkg/abi/linux"
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)
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func (ep *Endpoint) futexConnect(req *ctrlHandshakeRequest) (ctrlHandshakeResponse, error) {
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var resp ctrlHandshakeResponse
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// Write the handshake request.
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w := ep.NewWriter()
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if err := json.NewEncoder(w).Encode(req); err != nil {
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return resp, fmt.Errorf("error writing handshake request: %v", err)
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}
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*ep.dataLen() = w.Len()
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// Exchange control with the server.
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if err := ep.futexSwitchToPeer(); err != nil {
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return resp, err
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}
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if err := ep.futexSwitchFromPeer(); err != nil {
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return resp, err
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}
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// Read the handshake response.
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respLen := atomic.LoadUint32(ep.dataLen())
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if respLen > ep.dataCap {
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return resp, fmt.Errorf("invalid handshake response length %d (maximum %d)", respLen, ep.dataCap)
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}
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if err := json.NewDecoder(ep.NewReader(respLen)).Decode(&resp); err != nil {
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return resp, fmt.Errorf("error reading handshake response: %v", err)
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}
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return resp, nil
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}
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func (ep *Endpoint) futexSwitchToPeer() error {
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// Update connection state to indicate that the peer should be active.
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if !atomic.CompareAndSwapUint32(ep.connState(), ep.activeState, ep.inactiveState) {
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return fmt.Errorf("unexpected connection state before FUTEX_WAKE: %v", atomic.LoadUint32(ep.connState()))
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}
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// Wake the peer's Endpoint.futexSwitchFromPeer().
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if err := ep.futexWakeConnState(1); err != nil {
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return fmt.Errorf("failed to FUTEX_WAKE peer Endpoint: %v", err)
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}
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return nil
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}
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func (ep *Endpoint) futexSwitchFromPeer() error {
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for {
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switch cs := atomic.LoadUint32(ep.connState()); cs {
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case ep.activeState:
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return nil
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case ep.inactiveState:
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// Continue to FUTEX_WAIT.
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default:
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return fmt.Errorf("unexpected connection state before FUTEX_WAIT: %v", cs)
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}
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if ep.isShutdownLocally() {
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return shutdownError{}
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}
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if err := ep.futexWaitConnState(ep.inactiveState); err != nil {
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return fmt.Errorf("failed to FUTEX_WAIT for peer Endpoint: %v", err)
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}
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}
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}
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func (ep *Endpoint) futexWakeConnState(numThreads int32) error {
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if _, _, e := syscall.RawSyscall(syscall.SYS_FUTEX, ep.packet, linux.FUTEX_WAKE, uintptr(numThreads)); e != 0 {
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return e
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}
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return nil
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}
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func (ep *Endpoint) futexWaitConnState(curState uint32) error {
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_, _, e := syscall.Syscall6(syscall.SYS_FUTEX, ep.packet, linux.FUTEX_WAIT, uintptr(curState), 0, 0, 0)
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if e != 0 && e != syscall.EAGAIN && e != syscall.EINTR {
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return e
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}
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return nil
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}
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func yieldThread() {
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syscall.Syscall(syscall.SYS_SCHED_YIELD, 0, 0, 0)
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// The thread we're trying to yield to may be waiting for a Go runtime P.
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// runtime.Gosched() will hand off ours if necessary.
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runtime.Gosched()
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}
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