link: return os.ErrNotExist when symbol doesn't exist

Some of the tracing related links currently return ErrNotSupported
when trying to attach to a non-existant symbol. This is misleading.
Consistently return os.ErrNotExist in such cases.

Author: lmb

link/kprobe.go

@@ -266,8 +266,7 @@ func tracefsProbe(typ probeType, symbol, path string, offset uint64, ret bool) (
 	if err == nil {
 		return nil, fmt.Errorf("trace event already exists: %s/%s", group, symbol)
 	}
-	// The read is expected to fail with ErrNotSupported due to a non-existing event.
-	if err != nil && !errors.Is(err, ErrNotSupported) {
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
 		return nil, fmt.Errorf("checking trace event %s/%s: %w", group, symbol, err)
 	}
 
@@ -346,7 +345,7 @@ func createTraceFSProbeEvent(typ probeType, group, symbol, path string, offset u
 	// when trying to create a kretprobe for a missing symbol. Make sure ENOENT
 	// is returned to the caller.
 	if errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.EINVAL) {
-		return fmt.Errorf("kernel symbol %s not found: %w", symbol, os.ErrNotExist)
+		return fmt.Errorf("symbol %s not found: %w", symbol, os.ErrNotExist)
 	}
 	if err != nil {
 		return fmt.Errorf("writing '%s' to '%s': %w", pe, typ.EventsPath(), err)

link/perf_event.go

@@ -207,8 +207,8 @@ func unsafeStringPtr(str string) (unsafe.Pointer, error) {
 // group and name must be alphanumeric or underscore, as required by the kernel.
 func getTraceEventID(group, name string) (uint64, error) {
 	tid, err := uint64FromFile(tracefsPath, "events", group, name, "id")
-	if errors.Is(err, ErrNotSupported) {
-		return 0, fmt.Errorf("trace event %s/%s: %w", group, name, ErrNotSupported)
+	if errors.Is(err, os.ErrNotExist) {
+		return 0, fmt.Errorf("trace event %s/%s: %w", group, name, os.ErrNotExist)
 	}
 	if err != nil {
 		return 0, fmt.Errorf("reading trace event ID of %s/%s: %w", group, name, err)
@@ -219,9 +219,11 @@ func getTraceEventID(group, name string) (uint64, error) {
 
 // getPMUEventType reads a Performance Monitoring Unit's type (numeric identifier)
 // from /sys/bus/event_source/devices/<pmu>/type.
+//
+// Returns ErrNotSupported if the pmu type is not supported.
 func getPMUEventType(typ probeType) (uint64, error) {
 	et, err := uint64FromFile("/sys/bus/event_source/devices", typ.String(), "type")
-	if errors.Is(err, ErrNotSupported) {
+	if errors.Is(err, os.ErrNotExist) {
 		return 0, fmt.Errorf("pmu type %s: %w", typ, ErrNotSupported)
 	}
 	if err != nil {
@@ -255,22 +257,13 @@ func openTracepointPerfEvent(tid uint64) (*internal.FD, error) {
 // and joined onto base. Returns error if base no longer prefixes the path after
 // joining all components.
 func uint64FromFile(base string, path ...string) (uint64, error) {
-
-	// Resolve leaf path separately for error feedback. Makes the join onto
-	// base more readable (can't mix with variadic args).
 	l := filepath.Join(path...)
-
 	p := filepath.Join(base, l)
 	if !strings.HasPrefix(p, base) {
 		return 0, fmt.Errorf("path '%s' attempts to escape base path '%s': %w", l, base, errInvalidInput)
 	}
 
 	data, err := ioutil.ReadFile(p)
-	if os.IsNotExist(err) {
-		// Only echo leaf path, the base path can be prepended at the call site
-		// if more verbosity is required.
-		return 0, fmt.Errorf("symbol %s: %w", l, ErrNotSupported)
-	}
 	if err != nil {
 		return 0, fmt.Errorf("reading file %s: %w", p, err)
 	}

link/perf_event_test.go

@@ -2,6 +2,7 @@ package link
 
 import (
 	"errors"
+	"os"
 	"testing"
 
 	"github.com/cilium/ebpf/internal/testutils"
@@ -38,8 +39,8 @@ func TestTraceReadID(t *testing.T) {
 	}
 
 	_, err = uint64FromFile("/base/path/not", "../not/escaped")
-	if !errors.Is(err, ErrNotSupported) {
-		t.Errorf("expected error %s, got: %s", ErrNotSupported, err)
+	if !errors.Is(err, os.ErrNotExist) {
+		t.Errorf("expected os.ErrNotExist, got: %s", err)
 	}
 }
 

link/tracepoint_test.go

@@ -2,11 +2,11 @@ package link
 
 import (
 	"errors"
+	"os"
 	"testing"
 
 	"github.com/cilium/ebpf"
 	"github.com/cilium/ebpf/asm"
-	"github.com/cilium/ebpf/internal"
 	"github.com/cilium/ebpf/internal/testutils"
 	"github.com/cilium/ebpf/internal/unix"
 
@@ -48,6 +48,19 @@ func TestTracepoint(t *testing.T) {
 	}
 }
 
+func TestTracepointMissing(t *testing.T) {
+	prog, err := ebpf.NewProgram(&tracepointSpec)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer prog.Close()
+
+	_, err = Tracepoint("missing", "foobazbar", prog)
+	if !errors.Is(err, os.ErrNotExist) {
+		t.Error("Expected os.ErrNotExist, got", err)
+	}
+}
+
 func TestTracepointErrors(t *testing.T) {
 	c := qt.New(t)
 
@@ -72,8 +85,8 @@ func TestTraceGetEventID(t *testing.T) {
 	}
 
 	_, err = getTraceEventID("totally", "bogus")
-	if !errors.Is(err, internal.ErrNotSupported) {
-		t.Fatal("Doesn't return ErrNotSupported")
+	if !errors.Is(err, os.ErrNotExist) {
+		t.Fatal("Expected os.ErrNotExist, got", err)
 	}
 }