[PATCH bpf-next v2 1/2] bpf: Add show_fdinfo for uprobe_multi

[Tao Chen <chen.dylane@linux.dev>]

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

link_type:	uprobe_multi
link_id:	9
prog_tag:	e729f789e34a8eca
prog_id:	58
type:	uprobe_multi
uprobe_cnt:	3
pid:	0
path:	/home/dylane/bpf/tools/testing/selftests/bpf/test_progs
offset:	0xa69ed7
ref_ctr_offset:	0x0
cookie:	3
offset:	0xa69ee2
ref_ctr_offset:	0x0
cookie:	1
offset:	0xa69eed
ref_ctr_offset:	0x0
cookie:	2

Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
 kernel/trace/bpf_trace.c | 48 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

Change list:
  v1 -> v2:
    - replace 'func_cnt' with 'uprobe_cnt'.(Andrii)
    - print func name is more readable and security for kprobe_multi.(Alexei)
  v1:
  https://lore.kernel.org/bpf/20250612115556.295103-1-chen.dylane@linux.dev

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 24b94870b50..9a8ca8a8e2b 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3157,10 +3157,58 @@ static int bpf_uprobe_multi_link_fill_link_info(const struct bpf_link *link,
 	return err;
 }
 
+#ifdef CONFIG_PROC_FS
+static void bpf_uprobe_multi_show_fdinfo(const struct bpf_link *link,
+					 struct seq_file *seq)
+{
+	struct bpf_uprobe_multi_link *umulti_link;
+	char *p, *buf;
+
+	umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
+
+	buf = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!buf)
+		return;
+
+	p = d_path(&umulti_link->path, buf, PATH_MAX);
+	if (IS_ERR(p)) {
+		kfree(buf);
+		return;
+	}
+
+	seq_printf(seq,
+		   "type:\t%s\n"
+		   "uprobe_cnt:\t%u\n"
+		   "pid:\t%u\n"
+		   "path:\t%s\n",
+		   umulti_link->flags == BPF_F_UPROBE_MULTI_RETURN ?
+					 "uretprobe_multi" : "uprobe_multi",
+		   umulti_link->cnt,
+		   umulti_link->task ? task_pid_nr_ns(umulti_link->task,
+			   task_active_pid_ns(current)) : 0,
+		   p);
+
+	for (int i = 0; i < umulti_link->cnt; i++) {
+		seq_printf(seq,
+			   "offset:\t%#llx\n"
+			   "ref_ctr_offset:\t%#lx\n"
+			   "cookie:\t%llu\n",
+			   umulti_link->uprobes[i].offset,
+			   umulti_link->uprobes[i].ref_ctr_offset,
+			   umulti_link->uprobes[i].cookie);
+	}
+
+	kfree(buf);
+}
+#endif
+
 static const struct bpf_link_ops bpf_uprobe_multi_link_lops = {
 	.release = bpf_uprobe_multi_link_release,
 	.dealloc_deferred = bpf_uprobe_multi_link_dealloc,
 	.fill_link_info = bpf_uprobe_multi_link_fill_link_info,
+#ifdef CONFIG_PROC_FS
+	.show_fdinfo = bpf_uprobe_multi_show_fdinfo,
+#endif
 };
 
 static int uprobe_prog_run(struct bpf_uprobe *uprobe,
-- 
2.48.1