netdev - [PATCH bpf-next] bpf: print a little more info about maps via cat /sys/fs/bpf/pinned

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Message-Id: <20220521075736.1225397-1-zenczykowski@gmail.com>
Date:   Sat, 21 May 2022 00:57:36 -0700
From:   Maciej Żenczykowski <zenczykowski@...il.com>
To:     Maciej Żenczykowski <maze@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Linux Network Development Mailing List <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        BPF Mailing List <bpf@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: [PATCH bpf-next] bpf: print a little more info about maps via cat /sys/fs/bpf/pinned_name

From: Maciej Żenczykowski <maze@...gle.com>

While this information can be fetched via bpftool,
the cli tool itself isn't always available on more limited systems.

>From the information printed particularly the 'id' is useful since
when combined with /proc/pid/fd/X and /proc/pid/fdinfo/X it allows
tracking down which bpf maps a process has open (which can be
useful for tracking down fd leaks).

Signed-off-by: Maciej Żenczykowski <maze@...gle.com>
---
 kernel/bpf/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index 4f841e16779e..784266e258fe 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -257,6 +257,9 @@ static int map_seq_show(struct seq_file *m, void *v)
 	if (unlikely(v == SEQ_START_TOKEN)) {
 		seq_puts(m, "# WARNING!! The output is for debug purpose only\n");
 		seq_puts(m, "# WARNING!! The output format will change\n");
+		seq_printf(m, "# type: %d, key_size: %d, value_size: %d, max_entries: %d, id: %d\n",
+			   map->map_type, map->key_size, map->value_size, map->max_entries,
+			   map->id);
 	} else {
 		map->ops->map_seq_show_elem(map, key, m);
 	}
-- 
2.36.1.124.g0e6072fb45-goog