Refactor code of attaching skb-tracking kprobe

Hide the attaching details of tracking skb from `main.go`.

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>

internal/pwru/skb_tracker.go

@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: Apache-2.0
+/* Copyright 2024 Authors of Cilium */
+
+package pwru
+
+import (
+	"errors"
+	"log"
+	"os"
+
+	"github.com/cilium/ebpf"
+	"github.com/cilium/ebpf/link"
+)
+
+type skbTracker struct {
+	links []link.Link
+}
+
+func (t *skbTracker) Close() {
+	for _, l := range t.links {
+		_ = l.Close()
+	}
+	t.links = nil
+}
+
+func TrackSkb(coll *ebpf.Collection, haveFexit bool) *skbTracker {
+	var t skbTracker
+
+	kp, err := link.Kprobe("kfree_skbmem", coll.Programs["kprobe_skb_lifetime_termination"], nil)
+	if err != nil {
+		if !errors.Is(err, os.ErrNotExist) {
+			log.Fatalf("Opening kprobe kfree_skbmem: %s\n", err)
+		} else {
+			log.Printf("Warn: kfree_skbmem not found, pwru is likely to mismatch skb due to lack of skb lifetime management\n")
+		}
+	} else {
+		t.links = append(t.links, kp)
+	}
+
+	if haveFexit {
+		progs := []*ebpf.Program{
+			coll.Programs["fexit_skb_clone"],
+			coll.Programs["fexit_skb_copy"],
+		}
+		for _, prog := range progs {
+			fexit, err := link.AttachTracing(link.TracingOptions{
+				Program: prog,
+			})
+			if err != nil {
+				if !errors.Is(err, os.ErrNotExist) {
+					log.Fatalf("Opening tracing(%s): %s\n", prog, err)
+				}
+			} else {
+				t.links = append(t.links, fexit)
+			}
+		}
+	}
+
+	return &t
+}

main.go

@@ -16,7 +16,6 @@ import (
 
 	"github.com/cilium/ebpf"
 	"github.com/cilium/ebpf/btf"
-	"github.com/cilium/ebpf/link"
 	"github.com/cilium/ebpf/rlimit"
 	"golang.org/x/sys/unix"
 
@@ -196,36 +195,9 @@ func main() {
 		defer close()
 	}
 
-	if flags.FilterTrackSkb {
-		kp, err := link.Kprobe("kfree_skbmem", coll.Programs["kprobe_skb_lifetime_termination"], nil)
-		if err != nil {
-			if !errors.Is(err, os.ErrNotExist) {
-				log.Fatalf("Opening kprobe kfree_skbmem: %s\n", err)
-			} else {
-				log.Printf("Warn: kfree_skbmem not found, pwru is likely to mismatch skb due to lack of skb lifetime management\n")
-			}
-		} else {
-			defer kp.Close()
-		}
-
-		if haveFexit {
-			progs := []*ebpf.Program{
-				coll.Programs["fexit_skb_clone"],
-				coll.Programs["fexit_skb_copy"],
-			}
-			for _, prog := range progs {
-				fexit, err := link.AttachTracing(link.TracingOptions{
-					Program: prog,
-				})
-				if err != nil {
-					if !errors.Is(err, os.ErrNotExist) {
-						log.Fatalf("Opening tracing(%s): %s\n", prog, err)
-					}
-				} else {
-					defer fexit.Close()
-				}
-			}
-		}
+	if flags.FilterTrackSkb && len(funcs) != 0 {
+		t := pwru.TrackSkb(coll, haveFexit)
+		defer t.Close()
 	}
 
 	if len(funcs) != 0 {