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

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Date:   Mon, 23 May 2022 13:14:31 -0700
From:   Maciej Żenczykowski <zenczykowski@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        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: Re: [PATCH bpf-next] bpf: print a little more info about maps via cat /sys/fs/bpf/pinned_name

On Mon, May 23, 2022 at 12:32 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Sat, May 21, 2022 at 12:57 AM Maciej Żenczykowski
> <zenczykowski@...il.com> wrote:
> >
> > 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);
>
> Maybe use cat /sys/fs/bpf/maps.debug instead?
> It prints map id.

Is this something that was very recently added?
I'm not seeing it on my 5.16 machine with bpffs mounted at /sys/fs/bpf.