[RFC PATCH bpf-next 1/8] bpf: Support ->show_fdinfo for kprobe_multi

[Yafang Shao <laoar.shao@xxxxxxxxx>]

Currently, there is no way to check which functions are attached to a
kprobe_multi link, causing confusion for users. It is important that we
provide a means to expose these functions. The expected result is as follows,

$ cat /proc/10936/fdinfo/9
pos:    0
flags:  02000000
mnt_id: 15
ino:    2094
link_type:      kprobe_multi
link_id:        2
prog_tag:       a04f5eef06a7f555
prog_id:        11
func_count:     4
func_addrs:     ffffffffaad475c0
                ffffffffaad47600
                ffffffffaad47640
                ffffffffaad47680

$ cat /proc/10936/fdinfo/9 | grep "func_addrs" -A 4 | \
  awk '{ if (NR ==1) {print $2} else {print $1}}' | \
  awk '{"grep " $1 " /proc/kallsyms"| getline f; print f}'
ffffffffaad475c0 T schedule_timeout_interruptible
ffffffffaad47600 T schedule_timeout_killable
ffffffffaad47640 T schedule_timeout_uninterruptible
ffffffffaad47680 T schedule_timeout_idle

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 kernel/trace/bpf_trace.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 2bc41e6..0d84a7a 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2548,9 +2548,26 @@ static void bpf_kprobe_multi_link_dealloc(struct bpf_link *link)
 	kfree(kmulti_link);
 }
 
+static void bpf_kprobe_multi_link_show_fdinfo(const struct bpf_link *link,
+				      struct seq_file *seq)
+{
+	struct bpf_kprobe_multi_link *kmulti_link;
+	int i;
+
+	kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
+	seq_printf(seq, "func_count:\t%d\n", kmulti_link->cnt);
+	for (i = 0; i < kmulti_link->cnt; i++) {
+		if (i == 0)
+			seq_printf(seq, "func_addrs:\t%lx\n", kmulti_link->addrs[i]);
+		else
+			seq_printf(seq, "           \t%lx\n", kmulti_link->addrs[i]);
+	}
+}
+
 static const struct bpf_link_ops bpf_kprobe_multi_link_lops = {
 	.release = bpf_kprobe_multi_link_release,
 	.dealloc = bpf_kprobe_multi_link_dealloc,
+	.show_fdinfo = bpf_kprobe_multi_link_show_fdinfo,
 };
 
 static void bpf_kprobe_multi_cookie_swap(void *a, void *b, int size, const void *priv)
-- 
1.8.3.1