[PATCH bpf-next v2 13/21] bpf: Add tracing_multi link fdinfo support for bpf progs

[Leon Hwang <leon.hwang@linux.dev>]

Show the target bpf prog info in the fdinfo.

$ cat /proc/self/fdinfo/13
pos:	0
flags:	02000000
mnt_id:	18
ino:	1045
link_type:	tracing_multi
link_id:	9
prog_tag:	9a7f9e3ab6f138ab
prog_id:	25
attach_type:	61
cnt:	2
prog-id	 btf-id	 cookie	 func
21	 4	 16706819	 target_1
22	 5	 16706819	 target_2

Different from the fdinfo of link whose targets are kernel functions, here
shows 'prog-id' instead of 'obj-id' to describe the ID of the target bpf
progs. And, 'func' shows the concrete function name of the target bpf
progs, because the function name can be retrieved by bpftool via 'prog-id'
+ 'btf-id'.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 kernel/trace/bpf_trace.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d4af42e25fe5..8b1a52350cfd 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3761,26 +3761,45 @@ static int bpf_tracing_multi_link_fill_link_info(const struct bpf_link *link,
 }
 
 #ifdef CONFIG_PROC_FS
+static const char *bpf_prog_func_name(struct bpf_prog *prog, u32 btf_id)
+{
+	const struct btf *btf = prog->aux->btf;
+	const struct btf_type *t;
+
+	t = btf_type_by_id(btf, btf_id);
+	if (!t || !btf_type_is_func(t))
+		return "";
+
+	return btf_name_by_offset(btf, t->name_off);
+}
+
 static void bpf_tracing_multi_show_fdinfo(const struct bpf_link *link,
 					  struct seq_file *seq)
 {
 	struct bpf_tracing_multi_link *tr_link =
 		container_of(link, struct bpf_tracing_multi_link, link);
 	bool has_cookies = !!tr_link->cookies;
+	bool has_progs = !!tr_link->tgt_progs;
 
 	seq_printf(seq, "attach_type:\t%u\n", tr_link->link.attach_type);
 	seq_printf(seq, "cnt:\t%u\n", tr_link->nodes_cnt);
 
-	seq_printf(seq, "%s\t %s\t %s\t %s\n", "obj-id", "btf-id", "cookie", "func");
+	seq_printf(seq, "%s\t %s\t %s\t %s\n", has_progs ? "prog-id" : "obj-id", "btf-id", "cookie",
+		   "func");
 	for (int i = 0; i < tr_link->nodes_cnt; i++) {
 		struct bpf_tracing_multi_node *mnode = &tr_link->nodes[i];
+		u64 cookie = has_cookies ? tr_link->cookies[i] : 0;
 		u32 btf_id, obj_id;
 
 		bpf_trampoline_unpack_key(mnode->trampoline->key, &obj_id, &btf_id);
-		seq_printf(seq, "%u\t %u\t %llu\t %pS\n",
-			   obj_id, btf_id,
-			   has_cookies ? tr_link->cookies[i] : 0,
-			   (void *) mnode->trampoline->ip);
+		if (has_progs)
+			seq_printf(seq, "%u\t %u\t %llu\t %s\n",
+				   obj_id, btf_id, cookie,
+				   bpf_prog_func_name(tr_link->tgt_progs[i], btf_id));
+		else
+			seq_printf(seq, "%u\t %u\t %llu\t %pS\n",
+				   obj_id, btf_id, cookie,
+				   (void *) mnode->trampoline->ip);
 
 		cond_resched();
 	}
-- 
2.55.0