bpf: Add show_fdinfo for kprobe_multi

Show kprobe_multi link info with fdinfo, the info as follows:

link_type:	kprobe_multi
link_id:	1
prog_tag:	a69740b9746f7da8
prog_id:	21
kprobe_cnt:	8
missed:	0
cookie	 func
1	 bpf_fentry_test1+0x0/0x20
7	 bpf_fentry_test2+0x0/0x20
2	 bpf_fentry_test3+0x0/0x20
3	 bpf_fentry_test4+0x0/0x20
4	 bpf_fentry_test5+0x0/0x20
5	 bpf_fentry_test6+0x0/0x20
6	 bpf_fentry_test7+0x0/0x20
8	 bpf_fentry_test8+0x0/0x10

Signed-off-by: Tao Chen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: Tao Chen

kernel/trace/bpf_trace.c

@@ -2619,10 +2619,37 @@ static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
 	return err;
 }
 
+#ifdef CONFIG_PROC_FS
+static void bpf_kprobe_multi_show_fdinfo(const struct bpf_link *link,
+					 struct seq_file *seq)
+{
+	struct bpf_kprobe_multi_link *kmulti_link;
+
+	kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
+
+	seq_printf(seq,
+		   "kprobe_cnt:\t%u\n"
+		   "missed:\t%lu\n",
+		   kmulti_link->cnt,
+		   kmulti_link->fp.nmissed);
+
+	seq_printf(seq, "%s\t %s\n", "cookie", "func");
+	for (int i = 0; i < kmulti_link->cnt; i++) {
+		seq_printf(seq,
+			   "%llu\t %pS\n",
+			   kmulti_link->cookies[i],
+			   (void *)kmulti_link->addrs[i]);
+	}
+}
+#endif
+
 static const struct bpf_link_ops bpf_kprobe_multi_link_lops = {
 	.release = bpf_kprobe_multi_link_release,
 	.dealloc_deferred = bpf_kprobe_multi_link_dealloc,
 	.fill_link_info = bpf_kprobe_multi_link_fill_link_info,
+#ifdef CONFIG_PROC_FS
+	.show_fdinfo = bpf_kprobe_multi_show_fdinfo,
+#endif
 };
 
 static void bpf_kprobe_multi_cookie_swap(void *a, void *b, int size, const void *priv)