bpf: Add show_fdinfo for uprobe_multi

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

link_type:	uprobe_multi
link_id:	9
prog_tag:	e729f789e34a8eca
prog_id:	39
uprobe_cnt:	3
pid:	0
path:	/home/dylane/bpf/tools/testing/selftests/bpf/test_progs
cookie	 offset	 ref_ctr_offset
3	 0xa69f13	 0x0
1	 0xa69f1e	 0x0
2	 0xa69f29	 0x0

Signed-off-by: Tao Chen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: Tao Chen

kernel/trace/bpf_trace.c

@@ -3152,10 +3152,54 @@ 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;
+	pid_t pid;
+
+	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;
+	}
+
+	pid = umulti_link->task ?
+	      task_pid_nr_ns(umulti_link->task, task_active_pid_ns(current)) : 0;
+	seq_printf(seq,
+		   "uprobe_cnt:\t%u\n"
+		   "pid:\t%u\n"
+		   "path:\t%s\n",
+		   umulti_link->cnt, pid, p);
+
+	seq_printf(seq, "%s\t %s\t %s\n", "cookie", "offset", "ref_ctr_offset");
+	for (int i = 0; i < umulti_link->cnt; i++) {
+		seq_printf(seq,
+			   "%llu\t %#llx\t %#lx\n",
+			   umulti_link->uprobes[i].cookie,
+			   umulti_link->uprobes[i].offset,
+			   umulti_link->uprobes[i].ref_ctr_offset);
+	}
+
+	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,