2019-04-29 21:25:05 +00:00
|
|
|
// Copyright 2018 The gVisor Authors.
|
2018-04-27 17:37:02 +00:00
|
|
|
//
|
|
|
|
// 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 sighandling contains helpers for handling signals to applications.
|
|
|
|
package sighandling
|
|
|
|
|
|
|
|
import (
|
2018-06-21 21:53:05 +00:00
|
|
|
"fmt"
|
2018-04-27 17:37:02 +00:00
|
|
|
"os"
|
|
|
|
"os/signal"
|
|
|
|
"reflect"
|
|
|
|
"syscall"
|
|
|
|
|
2019-06-13 23:49:09 +00:00
|
|
|
"gvisor.dev/gvisor/pkg/abi/linux"
|
2018-04-27 17:37:02 +00:00
|
|
|
)
|
|
|
|
|
|
|
|
// numSignals is the number of normal (non-realtime) signals on Linux.
|
|
|
|
const numSignals = 32
|
|
|
|
|
2018-10-17 19:27:58 +00:00
|
|
|
// handleSignals listens for incoming signals and calls the given handler
|
|
|
|
// function.
|
2018-09-07 17:27:19 +00:00
|
|
|
//
|
|
|
|
// It starts when the start channel is closed, stops when the stop channel
|
|
|
|
// is closed, and closes done once it will no longer deliver signals to k.
|
2018-10-17 19:27:58 +00:00
|
|
|
func handleSignals(sigchans []chan os.Signal, handler func(linux.Signal), start, stop, done chan struct{}) {
|
2018-04-27 17:37:02 +00:00
|
|
|
// Build a select case.
|
2018-06-15 20:37:21 +00:00
|
|
|
sc := []reflect.SelectCase{{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(start)}}
|
2018-04-27 17:37:02 +00:00
|
|
|
for _, sigchan := range sigchans {
|
|
|
|
sc = append(sc, reflect.SelectCase{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(sigchan)})
|
|
|
|
}
|
|
|
|
|
2018-06-15 20:37:21 +00:00
|
|
|
started := false
|
2018-04-27 17:37:02 +00:00
|
|
|
for {
|
|
|
|
// Wait for a notification.
|
|
|
|
index, _, ok := reflect.Select(sc)
|
|
|
|
|
2018-06-15 20:37:21 +00:00
|
|
|
// Was it the start / stop channel?
|
2018-04-27 17:37:02 +00:00
|
|
|
if index == 0 {
|
|
|
|
if !ok {
|
2018-09-07 17:27:19 +00:00
|
|
|
if !started {
|
|
|
|
// start channel; start forwarding and
|
|
|
|
// swap this case for the stop channel
|
|
|
|
// to select stop requests.
|
2018-06-15 20:37:21 +00:00
|
|
|
started = true
|
|
|
|
sc[0] = reflect.SelectCase{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(stop)}
|
2018-09-07 17:27:19 +00:00
|
|
|
} else {
|
|
|
|
// stop channel; stop forwarding and
|
|
|
|
// clear this case so it is never
|
|
|
|
// selected again.
|
|
|
|
started = false
|
|
|
|
close(done)
|
|
|
|
sc[0].Chan = reflect.Value{}
|
2018-06-15 20:37:21 +00:00
|
|
|
}
|
2018-04-27 17:37:02 +00:00
|
|
|
}
|
|
|
|
continue
|
|
|
|
}
|
|
|
|
|
|
|
|
// How about a different close?
|
|
|
|
if !ok {
|
|
|
|
panic("signal channel closed unexpectedly")
|
|
|
|
}
|
|
|
|
|
|
|
|
// Otherwise, it was a signal on channel N. Index 0 represents the stop
|
|
|
|
// channel, so index N represents the channel for signal N.
|
2018-06-21 21:53:05 +00:00
|
|
|
signal := linux.Signal(index)
|
|
|
|
|
|
|
|
if !started {
|
2018-09-07 17:27:19 +00:00
|
|
|
// Kernel cannot receive signals, either because it is
|
|
|
|
// not ready yet or is shutting down.
|
2018-04-27 17:37:02 +00:00
|
|
|
//
|
|
|
|
// Kill ourselves if this signal would have killed the
|
2018-06-15 20:37:21 +00:00
|
|
|
// process before PrepareForwarding was called. i.e., all
|
2018-04-27 17:37:02 +00:00
|
|
|
// _SigKill signals; see Go
|
|
|
|
// src/runtime/sigtab_linux_generic.go.
|
|
|
|
//
|
|
|
|
// Otherwise ignore the signal.
|
|
|
|
//
|
2019-04-29 21:03:04 +00:00
|
|
|
// TODO(b/114489875): Drop in Go 1.12, which uses tgkill
|
2018-09-08 01:13:50 +00:00
|
|
|
// in runtime.raise.
|
2018-06-21 21:53:05 +00:00
|
|
|
switch signal {
|
2018-04-27 17:37:02 +00:00
|
|
|
case linux.SIGHUP, linux.SIGINT, linux.SIGTERM:
|
2018-06-21 21:53:05 +00:00
|
|
|
dieFromSignal(signal)
|
|
|
|
panic(fmt.Sprintf("Failed to die from signal %d", signal))
|
|
|
|
default:
|
|
|
|
continue
|
2018-04-27 17:37:02 +00:00
|
|
|
}
|
|
|
|
}
|
2018-06-21 21:53:05 +00:00
|
|
|
|
2018-10-17 19:27:58 +00:00
|
|
|
// Pass the signal to the handler.
|
|
|
|
handler(signal)
|
2018-04-27 17:37:02 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2018-10-17 19:27:58 +00:00
|
|
|
// PrepareHandler ensures that synchronous signals are passed to the given
|
|
|
|
// handler function and returns a callback that starts signal delivery, which
|
|
|
|
// itself returns a callback that stops signal handling.
|
2018-09-07 17:27:19 +00:00
|
|
|
//
|
|
|
|
// Note that this function permanently takes over signal handling. After the
|
|
|
|
// stop callback, signals revert to the default Go runtime behavior, which
|
|
|
|
// cannot be overridden with external calls to signal.Notify.
|
2018-10-17 19:27:58 +00:00
|
|
|
func PrepareHandler(handler func(linux.Signal)) func() func() {
|
2018-06-15 20:37:21 +00:00
|
|
|
start := make(chan struct{})
|
2018-04-27 17:37:02 +00:00
|
|
|
stop := make(chan struct{})
|
2018-09-07 17:27:19 +00:00
|
|
|
done := make(chan struct{})
|
2018-04-27 17:37:02 +00:00
|
|
|
|
|
|
|
// Register individual channels. One channel per standard signal is
|
|
|
|
// required as os.Notify() is non-blocking and may drop signals. To avoid
|
|
|
|
// this, standard signals have to be queued separately. Channel size 1 is
|
|
|
|
// enough for standard signals as their semantics allow de-duplication.
|
|
|
|
//
|
|
|
|
// External real-time signals are not supported. We rely on the go-runtime
|
|
|
|
// for their handling.
|
|
|
|
var sigchans []chan os.Signal
|
|
|
|
for sig := 1; sig <= numSignals+1; sig++ {
|
|
|
|
sigchan := make(chan os.Signal, 1)
|
|
|
|
sigchans = append(sigchans, sigchan)
|
|
|
|
signal.Notify(sigchan, syscall.Signal(sig))
|
|
|
|
}
|
|
|
|
// Start up our listener.
|
2018-10-17 19:27:58 +00:00
|
|
|
go handleSignals(sigchans, handler, start, stop, done) // S/R-SAFE: synchronized by Kernel.extMu.
|
2018-06-15 20:37:21 +00:00
|
|
|
|
|
|
|
return func() func() {
|
|
|
|
close(start)
|
|
|
|
return func() {
|
|
|
|
close(stop)
|
2018-09-07 17:27:19 +00:00
|
|
|
<-done
|
2018-06-15 20:37:21 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
}
|