From c92a463f431cb7a50e1b6962197e982d4db5af6c Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Sat, 22 Jun 2024 07:54:03 +0000
Subject: [PATCH] link: allow pinning perf event based links

Support pinning of Kprobe and Uprobe links. It's not possible to
retrieve the perf event of a pinned link, so PerfEvent() now
returns an error.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 link/kprobe_multi.go |  8 --------
 link/link.go         |  2 +-
 link/perf_event.go   | 29 ++++++++++-------------------
 3 files changed, 11 insertions(+), 28 deletions(-)

diff --git a/link/kprobe_multi.go b/link/kprobe_multi.go
index 850c5f8b5..f7a8291f9 100644
--- a/link/kprobe_multi.go
+++ b/link/kprobe_multi.go
@@ -130,14 +130,6 @@ func (kml *kprobeMultiLink) Update(prog *ebpf.Program) error {
 	return fmt.Errorf("update kprobe_multi: %w", ErrNotSupported)
 }
 
-func (kml *kprobeMultiLink) Pin(string) error {
-	return fmt.Errorf("pin kprobe_multi: %w", ErrNotSupported)
-}
-
-func (kml *kprobeMultiLink) Unpin() error {
-	return fmt.Errorf("unpin kprobe_multi: %w", ErrNotSupported)
-}
-
 func (kml *kprobeMultiLink) Info() (*Info, error) {
 	var info sys.KprobeMultiLinkInfo
 	if err := sys.ObjInfo(kml.fd, &info); err != nil {
diff --git a/link/link.go b/link/link.go
index 9e8ca49c6..9c34616c9 100644
--- a/link/link.go
+++ b/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:
diff --git a/link/perf_event.go b/link/perf_event.go
index 89eab233b..1d8feb58c 100644
--- a/link/perf_event.go
+++ b/link/perf_event.go
@@ -99,30 +99,16 @@ 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) Unpin() error {
-	return fmt.Errorf("perf event link unpin: %w", ErrNotSupported)
-}
-
 func (pl *perfEventLink) Close() error {
 	if err := pl.fd.Close(); err != nil {
 		return fmt.Errorf("perf link close: %w", err)
 	}
 
+	// when created from pinned link
+	if pl.pe == nil {
+		return nil
+	}
+
 	if err := pl.pe.Close(); err != nil {
 		return fmt.Errorf("perf event close: %w", err)
 	}
@@ -136,6 +122,11 @@ func (pl *perfEventLink) Update(prog *ebpf.Program) error {
 var _ PerfEvent = (*perfEventLink)(nil)
 
 func (pl *perfEventLink) PerfEvent() (*os.File, error) {
+	// when created from pinned link
+	if pl.pe == nil {
+		return nil, ErrNotSupported
+	}
+
 	fd, err := pl.pe.fd.Dup()
 	if err != nil {
 		return nil, err