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

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Message-ID: <20200704000617.mrkwrta2gwywgb7l@ast-mbp.dhcp.thefacebook.com>
Date:   Fri, 3 Jul 2020 17:06:17 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 02, 2020 at 08:34:17PM -0700, Linus Torvalds wrote:
> 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.

I think I will go with "debug" mount option then.
By default nothing will be preloaded, so de-facto /sys/fs/bpf/ will stay empty.