netdev - Re: [PATCH v5 bpf-next 06/10] tracepoint: compute num

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Message-ID: <543f953a-8284-68f0-6a22-ec2d5f247199@fb.com>
Date:   Mon, 26 Mar 2018 11:39:05 -0700
From:   Alexei Starovoitov <ast@...com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        netdev <netdev@...r.kernel.org>,
        kernel-team <kernel-team@...com>,
        linux-api <linux-api@...r.kernel.org>,
        "Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [PATCH v5 bpf-next 06/10] tracepoint: compute num_args at build
 time

On 3/26/18 11:11 AM, Steven Rostedt wrote:
> On Mon, 26 Mar 2018 10:55:51 -0700
> Alexei Starovoitov <ast@...com> wrote:
>
>> An email ago you were ok to s/return/return NULL/ in your out-of-tree
>> module, but now flip flop to add new function approach just to
>> reduce the work you need to do in lttng?
>> We're not talking about changing __kmalloc signature here.
>> My patch extends for_each_kernel_tracepoint() api similar to other
>> for_each_*() iterators and improves possible uses of it.
>
> Alexei, do you have another use case for using
> for_each_kernel_tracepoint() other than the find_tp? If so, then I'm
> sure Mathieu can handle the change.
>
> But I think it's cleaner to add a tracepoint_find_by_name() function.
> If you come up with another use case for using the for_each* function
> then we'll consider changing it then.

another use case ?! Frankly such reasoning smells.

I'm fine doing quick followup patch to add tracepoint_find_by_name()
and restore 'return void' behavior of for_each_kernel_tracepoint's
callback, but I'm struggling to accept the precedent it will create
that all exported functions of kernel/tracepoint.c are really
lttng extensions and we cannot easily change them.
I'd like to hear Linus take on this.