cli: Backtrace on SIGUSR1

Rework the signal handling code so that if debug is enabled and a
`SIGUSR1` signal is received, backtrace to the system log but continue
to run.

Added some basic tests for the signal handling code.

Fixes #241.

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

cli/signals_test.go

@@ -0,0 +1,127 @@
+// Copyright (c) 2018 Intel Corporation
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package main
+
+import (
+	"bytes"
+	"reflect"
+	goruntime "runtime"
+	"sort"
+	"strings"
+	"syscall"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSignalFatalSignal(t *testing.T) {
+	assert := assert.New(t)
+
+	for sig, fatal := range handledSignalsMap {
+		result := nonFatalSignal(sig)
+		if fatal {
+			assert.False(result)
+		} else {
+			assert.True(result)
+		}
+	}
+}
+
+func TestSignalHandledSignalsMap(t *testing.T) {
+	assert := assert.New(t)
+
+	for sig, fatal := range handledSignalsMap {
+		result := fatalSignal(sig)
+		if fatal {
+			assert.True(result)
+		} else {
+			assert.False(result)
+		}
+	}
+}
+
+func TestSignalHandledSignals(t *testing.T) {
+	assert := assert.New(t)
+
+	var expected []syscall.Signal
+
+	for sig := range handledSignalsMap {
+		expected = append(expected, sig)
+	}
+
+	got := handledSignals()
+
+	sort.Slice(expected, func(i, j int) bool {
+		return int(expected[i]) < int(expected[j])
+	})
+
+	sort.Slice(got, func(i, j int) bool {
+		return int(got[i]) < int(got[j])
+	})
+
+	assert.True(reflect.DeepEqual(expected, got))
+}
+
+func TestSignalNonFatalSignal(t *testing.T) {
+	assert := assert.New(t)
+
+	for sig, fatal := range handledSignalsMap {
+		result := nonFatalSignal(sig)
+		if fatal {
+			assert.False(result)
+		} else {
+			assert.True(result)
+		}
+	}
+}
+
+func TestSignalFatalSignalInvalidSignal(t *testing.T) {
+	assert := assert.New(t)
+
+	sig := syscall.SIGXCPU
+
+	result := fatalSignal(sig)
+	assert.False(result)
+}
+
+func TestSignalNonFatalSignalInvalidSignal(t *testing.T) {
+	assert := assert.New(t)
+
+	sig := syscall.SIGXCPU
+
+	result := nonFatalSignal(sig)
+	assert.False(result)
+}
+
+func TestSignalBacktrace(t *testing.T) {
+	assert := assert.New(t)
+
+	// create buffer to save logger output
+	buf := &bytes.Buffer{}
+
+	savedOut := kataLog.Logger.Out
+	defer func() {
+		kataLog.Logger.Out = savedOut
+	}()
+
+	// capture output to buffer
+	kataLog.Logger.Out = buf
+
+	// determine name of *this* function
+	pc := make([]uintptr, 1)
+	goruntime.Callers(1, pc)
+	fn := goruntime.FuncForPC(pc[0])
+	name := fn.Name()
+
+	backtrace()
+
+	b := buf.String()
+
+	// very basic tests to check if a backtrace was produced
+	assert.True(strings.Contains(b, "contention:"))
+	assert.True(strings.Contains(b, `"level":"error"`))
+	assert.True(strings.Contains(b, name))
+}