Add support to pin kprobe link

Signed-off-by: Jiri Olsa <[email protected]>

link/link.go

@@ -119,7 +119,7 @@ func wrapRawLink(raw *RawLink) (_ Link, err error) {
 	case UprobeMultiType:
 		return &uprobeMultiLink{*raw}, nil
 	case PerfEventType:
-		return nil, fmt.Errorf("recovering perf event fd: %w", ErrNotSupported)
+		return &perfEventLink{*raw, nil}, nil
 	case TCXType:
 		return &tcxLink{*raw}, nil
 	case NetfilterType:

link/perf_event.go

@@ -99,30 +99,31 @@ type perfEventLink struct {
 
 func (pl *perfEventLink) isLink() {}
 
-// Pinning requires the underlying perf event FD to stay open.
-//
-// | PerfEvent FD | BpfLink FD | Works |
-// |--------------|------------|-------|
-// | Open         | Open       | Yes   |
-// | Closed       | Open       | No    |
-// | Open         | Closed     | No (Pin() -> EINVAL) |
-// | Closed       | Closed     | No (Pin() -> EINVAL) |
-//
-// There is currently no pretty way to recover the perf event FD
-// when loading a pinned link, so leave as not supported for now.
-func (pl *perfEventLink) Pin(string) error {
-	return fmt.Errorf("perf event link pin: %w", ErrNotSupported)
+func (pl *perfEventLink) Pin(fileName string) error {
+	if err := internal.Pin(pl.pinnedPath, fileName, pl.fd); err != nil {
+		return err
+	}
+	pl.pinnedPath = fileName
+	return nil
 }
 
 func (pl *perfEventLink) Unpin() error {
-	return fmt.Errorf("perf event link unpin: %w", ErrNotSupported)
+	if err := internal.Unpin(pl.pinnedPath); err != nil {
+		return err
+	}
+	pl.pinnedPath = ""
+	return nil
 }
 
 func (pl *perfEventLink) Close() error {
 	if err := pl.fd.Close(); err != nil {
 		return fmt.Errorf("perf link close: %w", err)
 	}
 
+	if pl.pe == nil {
+		return nil
+	}
+
 	if err := pl.pe.Close(); err != nil {
 		return fmt.Errorf("perf event close: %w", err)
 	}