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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Mon, 23 May 2022 13:21:16 -0700
Message-ID: <CAADnVQKWxzwAbZFAfOB2hxwOVP1mCfwpx30rcdRkCO-4DMxsZw@mail.gmail.com>
Subject: Re: [PATCH bpf-next] bpf: print a little more info about maps via cat /sys/fs/bpf/pinned_name
To:     =?UTF-8?Q?Maciej_=C5=BBenczykowski?= <zenczykowski@gmail.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Linux Network Development Mailing List 
        <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        BPF Mailing List <bpf@vger.kernel.org>,
        "David S . Miller" <davem@davemloft.net>
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On Mon, May 23, 2022 at 1:14 PM Maciej =C5=BBenczykowski
<zenczykowski@gmail.com> wrote:
>
> On Mon, May 23, 2022 at 12:32 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Sat, May 21, 2022 at 12:57 AM Maciej =C5=BBenczykowski
> > <zenczykowski@gmail.com> wrote:
> > >
> > > From: Maciej =C5=BBenczykowski <maze@google.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 =C5=BBenczykowski <maze@google.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 =3D=3D SEQ_START_TOKEN)) {
> > >                 seq_puts(m, "# WARNING!! The output is for debug purp=
ose only\n");
> > >                 seq_puts(m, "# WARNING!! The output format will chang=
e\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_s=
ize, 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.

It was there since 2020.
Make sure you have CONFIG_BPF_PRELOAD.