netdev - Re: [PATCH bpf-next 3/3] bpf: Add kernel module with user mode driver that populates bpffs.

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Message-ID: <CAHk-=wiBi3sjtL0JNzcPTYEOFomU9Oqz_vD=oHznxyQYGBRi5Q@mail.gmail.com>
Date:   Thu, 2 Jul 2020 20:34:17 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        kernel-team@...com
Subject: Re: [PATCH bpf-next 3/3] bpf: Add kernel module with user mode driver
 that populates bpffs.

On Thu, Jul 2, 2020 at 7:35 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Thu, Jul 02, 2020 at 06:05:29PM -0700, Linus Torvalds wrote:
> > On Thu, Jul 2, 2020 at 1:03 PM Alexei Starovoitov
> > <alexei.starovoitov@...il.com> wrote:
> > >
> > > The BPF program dump_bpf_prog() in iterators.bpf.c is printing this data about
> > > all BPF programs currently loaded in the system. This information is unstable
> > > and will change from kernel to kernel.
> >
> > If so, it should probably be in debugfs, not in /sys/fs/
>
> /sys/fs/bpf/ is just a historic location where we chose to mount bpffs.

It's more the "information is unstable and will change from kernel to kernel"

No such interfaces exist. If people start parsing it and depending it,
it's suddenly an ABI, whether you want to or not (and whether you
documented it or not).

At least if it's in /sys/kernel/debug/bpf/ or something, it's less
likely that anybody will do that.

               Linus