98 lines
3.1 KiB
Go
98 lines
3.1 KiB
Go
// Copyright 2018 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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// Package sighandling contains helpers for handling signals to applications.
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package sighandling
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import (
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"os"
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"os/signal"
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"reflect"
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"syscall"
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"gvisor.dev/gvisor/pkg/abi/linux"
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)
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// numSignals is the number of normal (non-realtime) signals on Linux.
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const numSignals = 32
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// handleSignals listens for incoming signals and calls the given handler
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// function.
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//
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// It stops when the stop channel is closed. The done channel is closed once it
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// will no longer deliver signals to k.
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func handleSignals(sigchans []chan os.Signal, handler func(linux.Signal), stop, done chan struct{}) {
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// Build a select case.
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sc := []reflect.SelectCase{{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(stop)}}
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for _, sigchan := range sigchans {
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sc = append(sc, reflect.SelectCase{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(sigchan)})
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}
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for {
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// Wait for a notification.
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index, _, ok := reflect.Select(sc)
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// Was it the stop channel?
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if index == 0 {
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if !ok {
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// Stop forwarding and notify that it's done.
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close(done)
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return
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}
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continue
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}
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// How about a different close?
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if !ok {
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panic("signal channel closed unexpectedly")
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}
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// Otherwise, it was a signal on channel N. Index 0 represents the stop
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// channel, so index N represents the channel for signal N.
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handler(linux.Signal(index))
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}
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}
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// StartSignalForwarding ensures that synchronous signals are passed to the
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// given handler function and returns a callback that stops signal delivery.
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//
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// Note that this function permanently takes over signal handling. After the
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// stop callback, signals revert to the default Go runtime behavior, which
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// cannot be overridden with external calls to signal.Notify.
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func StartSignalForwarding(handler func(linux.Signal)) func() {
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stop := make(chan struct{})
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done := make(chan struct{})
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// Register individual channels. One channel per standard signal is
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// required as os.Notify() is non-blocking and may drop signals. To avoid
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// this, standard signals have to be queued separately. Channel size 1 is
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// enough for standard signals as their semantics allow de-duplication.
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//
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// External real-time signals are not supported. We rely on the go-runtime
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// for their handling.
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var sigchans []chan os.Signal
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for sig := 1; sig <= numSignals+1; sig++ {
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sigchan := make(chan os.Signal, 1)
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sigchans = append(sigchans, sigchan)
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signal.Notify(sigchan, syscall.Signal(sig))
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}
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// Start up our listener.
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go handleSignals(sigchans, handler, stop, done) // S/R-SAFE: synchronized by Kernel.extMu.
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return func() {
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close(stop)
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<-done
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}
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}
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