agent: Display trace details

Log the trace mode and type when tracing is enabled. The change makes it
clearer that static tracing is enabled when the agent parsers the kernel
command line (`config.go`) and dynamic tracing is enabled by gRPC (`grpc.go`).

Specifics of change:

- Rename variables to match the terms defined in `TRACING.md`.
- Pass trace mode and trace type arguments to `enableTracing()`.
- Change the tense of the message displayed by `enableTracing()` so that
  the message indicates that tracing *is* enabled, not *about to be*.

Fixes kata-containers#504.

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

config.go

@@ -17,14 +17,17 @@ import (
 )
 
 const (
-	optionPrefix       = "agent."
-	logLevelFlag       = optionPrefix + "log"
-	devModeFlag        = optionPrefix + "devmode"
-	traceModeFlag      = optionPrefix + "trace"
-	useVsockFlag       = optionPrefix + "use_vsock"
-	kernelCmdlineFile  = "/proc/cmdline"
-	traceValueIsolated = "isolated"
-	traceValueCollated = "collated"
+	optionPrefix      = "agent."
+	logLevelFlag      = optionPrefix + "log"
+	devModeFlag       = optionPrefix + "devmode"
+	traceModeFlag     = optionPrefix + "trace"
+	useVsockFlag      = optionPrefix + "use_vsock"
+	kernelCmdlineFile = "/proc/cmdline"
+	traceModeStatic   = "static"
+	traceModeDynamic  = "dynamic"
+	traceTypeIsolated = "isolated"
+	traceTypeCollated = "collated"
+	defaultTraceType  = traceTypeIsolated
 )
 
 type agentConfig struct {
@@ -77,7 +80,7 @@ func (c *agentConfig) parseCmdlineOption(option string) error {
 	}
 
 	if option == traceModeFlag {
-		enableTracing(false)
+		enableTracing(traceModeStatic, defaultTraceType)
 		return nil
 	}
 
@@ -99,10 +102,10 @@ func (c *agentConfig) parseCmdlineOption(option string) error {
 		}
 	case traceModeFlag:
 		switch split[valuePosition] {
-		case traceValueIsolated:
-			enableTracing(false)
-		case traceValueCollated:
-			enableTracing(true)
+		case traceTypeIsolated:
+			enableTracing(traceModeStatic, traceTypeIsolated)
+		case traceTypeCollated:
+			enableTracing(traceModeStatic, traceTypeCollated)
 		}
 	case useVsockFlag:
 		flag, err := strconv.ParseBool(split[valuePosition])
@@ -126,13 +129,16 @@ func (c *agentConfig) parseCmdlineOption(option string) error {
 
 }
 
-func enableTracing(enableCollatedTrace bool) {
-	agentLog.Info("enabling tracing")
-
+func enableTracing(traceMode, traceType string) {
 	tracing = true
 
 	// Enable in case this generates more trace spans
 	debug = true
 
-	collatedTrace = enableCollatedTrace
+	collatedTrace = traceType == traceTypeCollated
+
+	agentLog.WithFields(logrus.Fields{
+		"trace-mode": traceMode,
+		"trace-type": traceType,
+	}).Info("enabled tracing")
 }

config_test.go

@@ -206,11 +206,11 @@ func TestParseCmdlineOptionTracing(t *testing.T) {
 		{traceModeFlag + "=", false, false},
 
 		{traceModeFlag, true, false},
-		{traceModeFlag + "=" + traceValueIsolated, true, false},
-		{traceModeFlag + "=" + traceValueCollated, true, true},
+		{traceModeFlag + "=" + traceTypeIsolated, true, false},
+		{traceModeFlag + "=" + traceTypeCollated, true, true},
 
-		{traceModeFlag + "=" + traceValueIsolated + "x", false, false},
-		{traceModeFlag + "=" + traceValueCollated + "x", false, false},
+		{traceModeFlag + "=" + traceTypeIsolated + "x", false, false},
+		{traceModeFlag + "=" + traceTypeCollated + "x", false, false},
 	}
 
 	for i, d := range data {
@@ -259,12 +259,17 @@ func TestEnableTracing(t *testing.T) {
 	assert := assert.New(t)
 
 	type testData struct {
-		collatedTrace bool
+		traceMode           string
+		traceType           string
+		expectCollatedTrace bool
 	}
 
 	data := []testData{
-		{false},
-		{true},
+		{traceModeStatic, traceTypeIsolated, false},
+		{traceModeStatic, traceTypeCollated, true},
+
+		{traceModeDynamic, traceTypeIsolated, false},
+		{traceModeDynamic, traceTypeCollated, true},
 	}
 
 	for i, d := range data {
@@ -273,12 +278,12 @@ func TestEnableTracing(t *testing.T) {
 		collatedTrace = false
 		debug = false
 
-		enableTracing(d.collatedTrace)
+		enableTracing(d.traceMode, d.traceType)
 
 		assert.True(debug, "test %d (%+v)", i, d)
 		assert.True(tracing, "test %d (%+v)", i, d)
 
-		if d.collatedTrace {
+		if d.expectCollatedTrace {
 			assert.True(collatedTrace, "test %d (%+v)", i, d)
 		} else {
 			assert.False(collatedTrace, "test %d (%+v)", i, d)

grpc.go

@@ -1689,7 +1689,8 @@ func (a *agentGRPC) StartTracing(ctx context.Context, req *pb.StartTracingReques
 		return nil, grpcStatus.Error(codes.FailedPrecondition, "tracing already enabled")
 	}
 
-	enableTracing(false)
+	// The only trace type support for dynamic tracing is isolated.
+	enableTracing(traceModeDynamic, traceTypeIsolated)
 	startTracingCalled = true
 
 	var err error