[PATCH bpf-next v5 1/3] bpf: Show precise link_type for {uprobe,kprobe}_multi fdinfo

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

Alexei suggested, 'link_type' can be more precise and differentiate
for human in fdinfo. In fact BPF_LINK_TYPE_KPROBE_MULTI includes
kretprobe_multi type, the same as BPF_LINK_TYPE_UPROBE_MULTI, so we
can show it more concretely.

link_type:	kprobe_multi
link_id:	1
prog_tag:	d2b307e915f0dd37
...
link_type:	kretprobe_multi
link_id:	2
prog_tag:	ab9ea0545870781d
...
link_type:	uprobe_multi
link_id:	9
prog_tag:	e729f789e34a8eca
...
link_type:	uretprobe_multi
link_id:	10
prog_tag:	7db356c03e61a4d4

Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
 include/linux/trace_events.h | 10 ++++++++++
 kernel/bpf/syscall.c         |  9 ++++++++-
 kernel/trace/bpf_trace.c     | 28 ++++++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 1 deletion(-)

Change list:
  v4 -> v5:
    - Add patch1 to show precise link_type for
      {uprobe,kprobe}_multi.(Alexei)
    - patch2,3 just remove type field, which will be showed in
      link_type
  v4:
  https://lore.kernel.org/bpf/20250619034257.70520-1-chen.dylane@linux.dev

  v3 -> v4:
    - use %pS to print func info.(Alexei)
  v3:
  https://lore.kernel.org/bpf/20250616130233.451439-1-chen.dylane@linux.dev

  v2 -> v3:
    - show info in one line for multi events.(Jiri)
  v2:
  https://lore.kernel.org/bpf/20250615150514.418581-1-chen.dylane@linux.dev

  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/include/linux/trace_events.h b/include/linux/trace_events.h
index fa9cf4292df..951c91babbc 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -780,6 +780,8 @@ int bpf_get_perf_event_info(const struct perf_event *event, u32 *prog_id,
 			    unsigned long *missed);
 int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
 int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
+void bpf_kprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len);
+void bpf_uprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len);
 #else
 static inline unsigned int trace_call_bpf(struct trace_event_call *call, void *ctx)
 {
@@ -832,6 +834,14 @@ bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 {
 	return -EOPNOTSUPP;
 }
+static inline void
+bpf_kprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len)
+{
+}
+static inline void
+bpf_uprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len)
+{
+}
 #endif
 
 enum {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 51ba1a7aa43..43b821b37bc 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3226,9 +3226,16 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
 	const struct bpf_prog *prog = link->prog;
 	enum bpf_link_type type = link->type;
 	char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
+	char link_type[64] = {};
 
 	if (type < ARRAY_SIZE(bpf_link_type_strs) && bpf_link_type_strs[type]) {
-		seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]);
+		if (link->type == BPF_LINK_TYPE_KPROBE_MULTI)
+			bpf_kprobe_multi_link_type_show(link, link_type, sizeof(link_type));
+		else if (link->type == BPF_LINK_TYPE_UPROBE_MULTI)
+			bpf_uprobe_multi_link_type_show(link, link_type, sizeof(link_type));
+		else
+			strscpy(link_type, bpf_link_type_strs[type], sizeof(link_type));
+		seq_printf(m, "link_type:\t%s\n", link_type);
 	} else {
 		WARN_ONCE(1, "missing BPF_LINK_TYPE(...) for link type %u\n", type);
 		seq_printf(m, "link_type:\t<%u>\n", type);
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 24b94870b50..8ecb1a9f85d 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3016,7 +3016,21 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	kvfree(cookies);
 	return err;
 }
+
+void bpf_kprobe_multi_link_type_show(const struct bpf_link *link, char *link_type,
+				     int len)
+{
+	struct bpf_kprobe_multi_link *kmulti_link;
+
+	kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
+	strscpy(link_type, kmulti_link->flags == BPF_F_KPROBE_MULTI_RETURN ?
+				"kretprobe_multi" : "kprobe_multi", len);
+}
 #else /* !CONFIG_FPROBE */
+void bpf_kprobe_multi_link_type_show(const struct bpf_link *link, char *link_type,
+				     int len)
+{
+}
 int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 {
 	return -EOPNOTSUPP;
@@ -3407,7 +3421,21 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	path_put(&path);
 	return err;
 }
+
+void bpf_uprobe_multi_link_type_show(const struct bpf_link *link, char *link_type,
+				     int len)
+{
+	struct bpf_uprobe_multi_link *umulti_link;
+
+	umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
+	strscpy(link_type, umulti_link->flags == BPF_F_UPROBE_MULTI_RETURN ?
+				"uretprobe_multi" : "uprobe_multi", len);
+}
 #else /* !CONFIG_UPROBES */
+void bpf_uprobe_multi_link_type_show(const struct bpf_link *link, char *link_type,
+				     int len)
+{
+}
 int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 {
 	return -EOPNOTSUPP;
-- 
2.48.1