link: Add Info interface support for perf event kprobe link

Implementing Info function (Link interface) for perf event
kprobe link, it's now possibe to retrieve link's data with:

  pevent := info.PerfEvent()
  switch pevent.Type {
  case unix.BPF_PERF_EVENT_KPROBE, unix.BPF_PERF_EVENT_KRETPROBE:
          kp := pevent.Kprobe()
          addr, ok := kp.Address()
          addr, ok := kp.Flags()
          missed, ok := kp.Missed()
  }

At the moment we support/return only Addr/Flags/Missed data
returned by Address/Flags/Missed KprobeMultiInfo methods
respectively.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>

internal/sys/syscall.go

@@ -103,6 +103,10 @@ func (i *KprobeMultiLinkInfo) info() (unsafe.Pointer, uint32) {
 	return unsafe.Pointer(i), uint32(unsafe.Sizeof(*i))
 }
 
+func (i *KprobeLinkInfo) info() (unsafe.Pointer, uint32) {
+	return unsafe.Pointer(i), uint32(unsafe.Sizeof(*i))
+}
+
 var _ Info = (*BtfInfo)(nil)
 
 func (i *BtfInfo) info() (unsafe.Pointer, uint32) {

link/link.go

@@ -213,6 +213,29 @@ func (kpm *KprobeMultiInfo) Missed() (uint64, bool) {
 	return kpm.missed, kpm.count > 0
 }
 
+type PerfEventInfo struct {
+	Type  sys.PerfEventType
+	extra interface{}
+}
+
+func (r *PerfEventInfo) Kprobe() *KprobeInfo {
+	e, _ := r.extra.(*KprobeInfo)
+	return e
+}
+
+type KprobeInfo struct {
+	address uint64
+	missed  uint64
+}
+
+func (kp *KprobeInfo) Address() (uint64, bool) {
+	return kp.address, kp.address > 0
+}
+
+func (kp *KprobeInfo) Missed() (uint64, bool) {
+	return kp.missed, kp.address > 0
+}
+
 // Tracing returns tracing type-specific link info.
 //
 // Returns nil if the type-specific link info isn't available.
@@ -277,6 +300,14 @@ func (r Info) KprobeMulti() *KprobeMultiInfo {
 	return e
 }
 
+// PerfEvent returns perf-event type-specific link info.
+//
+// Returns nil if the type-specific link info isn't available.
+func (r Info) PerfEvent() *PerfEventInfo {
+	e, _ := r.extra.(*PerfEventInfo)
+	return e
+}
+
 // RawLink is the low-level API to bpf_link.
 //
 // You should consider using the higher level interfaces in this
@@ -452,8 +483,7 @@ func (l *RawLink) Info() (*Info, error) {
 		extra = &XDPInfo{
 			Ifindex: xdpInfo.Ifindex,
 		}
-	case RawTracepointType, IterType,
-		PerfEventType, UprobeMultiType:
+	case RawTracepointType, IterType, UprobeMultiType:
 		// Extra metadata not supported.
 	case TCXType:
 		var tcxInfo sys.TcxLinkInfo
@@ -494,6 +524,29 @@ func (l *RawLink) Info() (*Info, error) {
 			flags:  kprobeMultiInfo.Flags,
 			missed: kprobeMultiInfo.Missed,
 		}
+	case PerfEventType:
+		var perfEventInfo sys.PerfEventLinkInfo
+		if err := sys.ObjInfo(l.fd, &perfEventInfo); err != nil {
+			return nil, fmt.Errorf("perf event link info: %s", err)
+		}
+
+		var extra2 interface{}
+		switch perfEventInfo.PerfEventType {
+		case sys.BPF_PERF_EVENT_KPROBE, sys.BPF_PERF_EVENT_KRETPROBE:
+			var kprobeInfo sys.KprobeLinkInfo
+			if err := sys.ObjInfo(l.fd, &kprobeInfo); err != nil {
+				return nil, fmt.Errorf("kprobe multi link info: %s", err)
+			}
+			extra2 = &KprobeInfo{
+				address: kprobeInfo.Addr,
+				missed:  kprobeInfo.Missed,
+			}
+		}
+
+		extra = &PerfEventInfo{
+			Type:  perfEventInfo.PerfEventType,
+			extra: extra2,
+		}
 	default:
 		return nil, fmt.Errorf("unknown link info type: %d", info.Type)
 	}

link/link_test.go

@@ -286,6 +286,21 @@ func testLink(t *testing.T, link Link, prog *ebpf.Program) {
 				// NB: We don't check that missed is actually correct
 				// since it's not easy to trigger from tests.
 			}
+		case sys.BPF_LINK_TYPE_PERF_EVENT:
+			// test default Info data
+			pevent := info.PerfEvent()
+			switch pevent.Type {
+			case sys.BPF_PERF_EVENT_KPROBE, sys.BPF_PERF_EVENT_KRETPROBE:
+				kp := pevent.Kprobe()
+				if addr, ok := kp.Address(); ok {
+					qt.Assert(t, qt.Not(qt.Equals(addr, 0)))
+
+					_, ok := kp.Missed()
+					qt.Assert(t, qt.IsTrue(ok))
+					// NB: We don't check that missed is actually correct
+					// since it's not easy to trigger from tests.
+				}
+			}
 		}
 	})