netdev - Re: [RFC PATCH bpf-next 2/4] bpf: introduce BPF dispatcher

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Message-ID: <CAJ+HfNhFFkZ+uC+UPdJELgbGoQDbf-t1mqwgqSLOZw_Duk=8Vg@mail.gmail.com>
Date:   Mon, 18 Nov 2019 11:03:53 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf <bpf@...r.kernel.org>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Edward Cree <ecree@...arflare.com>
Subject: Re: [RFC PATCH bpf-next 2/4] bpf: introduce BPF dispatcher

On Fri, 15 Nov 2019 at 22:58, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
[...]
> > Another thought; I'm using the fentry nop as patch point, so it wont
> > play nice with other users of fentry atm -- but the plan is to move to
> > Steve's *_ftrace_direct work at some point, correct?
>
> Yes. I'll start playing with reg/mod/unreg_ftrace_direct on Monday.
> Steven has a bunch more in his tree for merging, so I cannot just pull
> all of ftrace api features into bpf-next. So "be nice to other fentry users"
> would have to be done during merge window or shortly after in bpf-next tree
> after window closes. I think it's fine.

Yup, I agree.

> In bpf dispatch case it's really
> one dummy function we're talking about. If it was marked 'notrace'
> from get go no one would blink. It's a dummy function not interesting
> for ftrac-ing and not interesting from live patching pov.
>

...but marking it with 'notrace' would remove the __fentry__ nop.
Anyways, the "be nice" approach is OK.