Fix tracefs bugs for handling non standard mount points and improve

error messages

Signed-off-by: Daniel Hodges <[email protected]>

events.go

@@ -21,13 +21,16 @@ const (
 // corresponding list of available events.
 func AvailableEvents() (map[string][]string, error) {
 	events := map[string][]string{}
-	// BUG(hodgesds): this should ideally check mounts for debugfs
-	rawEvents, err := fileToStrings(TracingDir + "/available_events")
-	// Events are colon delimited by type so parse the type and add sub
-	// events appropriately.
+	tracefsMount, err := TraceFSMount()
+	if err != nil {
+		return events, err
+	}
+	rawEvents, err := fileToStrings(tracefsMount + "/available_events")
 	if err != nil {
 		return events, err
 	}
+	// Events are colon delimited by type so parse the type and add sub
+	// events appropriately.
 	for _, rawEvent := range rawEvents {
 		splits := strings.Split(rawEvent, ":")
 		if len(splits) <= 1 {
@@ -46,13 +49,16 @@ func AvailableEvents() (map[string][]string, error) {
 // AvailableSubsystems returns a slice of available subsystems.
 func AvailableSubsystems() ([]string, error) {
 	subsystems := []string{}
-	// BUG(hodgesds): this should ideally check mounts for debugfs
-	rawEvents, err := fileToStrings(TracingDir + "/available_events")
-	// Events are colon delimited by type so parse the type and add sub
-	// events appropriately.
+	tracefsMount, err := TraceFSMount()
+	if err != nil {
+		return subsystems, err
+	}
+	rawEvents, err := fileToStrings(tracefsMount + "/available_events")
 	if err != nil {
 		return subsystems, err
 	}
+	// Events are colon delimited by type so parse the type and add sub
+	// events appropriately.
 	for _, rawEvent := range rawEvents {
 		splits := strings.Split(rawEvent, ":")
 		if len(splits) <= 1 {
@@ -65,22 +71,34 @@ func AvailableSubsystems() ([]string, error) {
 
 // AvailableTracers returns the list of available tracers.
 func AvailableTracers() ([]string, error) {
-	return fileToStrings(TracingDir + "/available_tracers")
+	tracefsMount, err := TraceFSMount()
+	if err != nil {
+		return []string{}, err
+	}
+	return fileToStrings(tracefsMount + "/available_tracers")
 }
 
 // CurrentTracer returns the current tracer.
 func CurrentTracer() (string, error) {
-	res, err := fileToStrings(TracingDir + "/current_tracer")
+	tracefsMount, err := TraceFSMount()
+	if err != nil {
+		return "", err
+	}
+	res, err := fileToStrings(tracefsMount + "/current_tracer")
 	return res[0], err
 }
 
 // GetTracepointConfig is used to get the configuration for a trace event.
 func GetTracepointConfig(subsystem, event string) (uint64, error) {
-	res, err := fileToStrings(
-		TracingDir + fmt.Sprintf("/events/%s/%s/id", subsystem, event))
+	tracefsMount, err := TraceFSMount()
 	if err != nil {
 		return 0, err
 	}
+	res, err := fileToStrings(
+		tracefsMount + fmt.Sprintf("/events/%s/%s/id", subsystem, event))
+	if err != nil {
+		return 0, fmt.Errorf("Failed to get tracepoint config for %s:%s: %q", subsystem, event, err)
+	}
 	return strconv.ParseUint(res[0], 10, 64)
 }
 
@@ -113,7 +131,7 @@ func ProfileTracepoint(subsystem, event string, pid, cpu int, opts ...int) (BPFP
 		eventOps,
 	)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("Failed to open perf event for PerfEventAttr %+v: %q", eventAttr, err)
 	}
 
 	return &profiler{

fs_utils.go

@@ -42,10 +42,10 @@ var (
 func TraceFSMount() (string, error) {
 	mounts, err := GetFSMount(TraceFS)
 	if err != nil {
-		return "", err
+		return "", fmt.Errorf("Failed to get tracefs mount: %s", err.Error())
 	}
 	if len(mounts) == 0 {
-		return "", ErrNoMount
+		return "", fmt.Errorf("Mount for tracefs not mounted")
 	}
 	return mounts[0], nil
 }
@@ -54,10 +54,10 @@ func TraceFSMount() (string, error) {
 func DebugFSMount() (string, error) {
 	mounts, err := GetFSMount(DebugFS)
 	if err != nil {
-		return "", err
+		return "", fmt.Errorf("Failed to find debugfs mount: %q", err)
 	}
 	if len(mounts) == 0 {
-		return "", ErrNoMount
+		return "", fmt.Errorf("Mount for debugfs not mounted")
 	}
 	return mounts[0], nil
 }
@@ -67,7 +67,7 @@ func GetFSMount(mountType string) ([]string, error) {
 	mounts := []string{}
 	file, err := os.Open(ProcMounts)
 	if err != nil {
-		return mounts, err
+		return mounts, fmt.Errorf("Failed to find mount type %s: %q", mountType, err)
 	}
 	scanner := bufio.NewScanner(file)
 	for scanner.Scan() {

group_profiler.go

@@ -64,7 +64,7 @@ func NewGroupProfiler(pid, cpu, opts int, eventAttrs ...unix.PerfEventAttr) (Gro
 				opts,
 			)
 			if err != nil {
-				return nil, err
+				return nil, fmt.Errorf("Failed to open perf event with PerfEventAttr %+v %q", eventAttr, err)
 			}
 			fds[i] = fd
 			continue
@@ -82,6 +82,7 @@ func NewGroupProfiler(pid, cpu, opts int, eventAttrs ...unix.PerfEventAttr) (Gro
 			opts,
 		)
 		if err != nil {
+			err = fmt.Errorf("Failed to open perf event with PerfEventAtter %+v: %q", eventAttr, err)
 			// cleanup any old Fds
 			for ii, fd2 := range fds {
 				if ii == i {

process_profile.go

@@ -227,7 +227,7 @@ func NewProfiler(profilerType uint32, config uint64, pid, cpu int, opts ...int)
 		eventOps,
 	)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("Failed to open perf event for PerfEventAttr %+v: %q", eventAttr, err)
 	}
 
 	return &profiler{