[RFC PATCH bpf-next 2/8] bpf: Support ->fill_link_info for kprobe_multi

[Yafang Shao <laoar.shao@xxxxxxxxx>]

By adding support for ->fill_link_info to the kprobe_multi link, users will
be able to inspect it using `bpftool link show`. This enhancement will
expose both the count of probed functions and their respective addresses to
the user.

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 include/uapi/linux/bpf.h       |  4 ++++
 kernel/trace/bpf_trace.c       | 31 +++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  4 ++++
 3 files changed, 39 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 9273c65..6be9b1d 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6434,6 +6434,10 @@ struct bpf_link_info {
 			__s32 priority;
 			__u32 flags;
 		} netfilter;
+		struct {
+			__aligned_u64 addrs;
+			__u32 count;
+		} kprobe_multi;
 	};
 } __attribute__((aligned(8)));
 
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 0d84a7a..00a0009 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2564,10 +2564,41 @@ static void bpf_kprobe_multi_link_show_fdinfo(const struct bpf_link *link,
 	}
 }
 
+static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
+						struct bpf_link_info *info)
+{
+	struct bpf_kprobe_multi_link *kmulti_link;
+	u64 *uaddrs = u64_to_user_ptr(info->kprobe_multi.addrs);
+	u32 ucount = info->kprobe_multi.count;
+	int i;
+
+	if (!uaddrs ^ !ucount)
+		return -EINVAL;
+
+	kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
+	if (!uaddrs) {
+		info->kprobe_multi.count = kmulti_link->cnt;
+		return 0;
+	}
+
+	if (!ucount)
+		return 0;
+
+	if (ucount != kmulti_link->cnt)
+		return -EINVAL;
+
+	for (i = 0; i < ucount; i++)
+		if (copy_to_user(uaddrs + i, kmulti_link->addrs + i,
+				 sizeof(u64)))
+			return -EFAULT;
+	return 0;
+}
+
 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,
+	.fill_link_info = bpf_kprobe_multi_link_fill_link_info,
 };
 
 static void bpf_kprobe_multi_cookie_swap(void *a, void *b, int size, const void *priv)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 9273c65..6be9b1d 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6434,6 +6434,10 @@ struct bpf_link_info {
 			__s32 priority;
 			__u32 flags;
 		} netfilter;
+		struct {
+			__aligned_u64 addrs;
+			__u32 count;
+		} kprobe_multi;
 	};
 } __attribute__((aligned(8)));
 
-- 
1.8.3.1