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

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Message-ID: <20180326144821.20f6b0de@gandalf.local.home>
Date:   Mon, 26 Mar 2018 14:48:21 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <ast@...com>
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 Mon, 26 Mar 2018 11:39:05 -0700
Alexei Starovoitov <ast@...com> wrote:

> 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.

WTF is the big deal here?

> 
> I'm fine doing quick followup patch to add tracepoint_find_by_name()

And BTW, it would actually have to be called
tracepoint_core_find_by_name() as it will not deal with modules.
Modules would have to have much more work to deal with.

> and restore 'return void' behavior of for_each_kernel_tracepoint's

What? you can't rebase now? Just don't touch that function.

> 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.

First, my argument about your use case has little to do with LTTng.
I have to maintain this code, and this is my preference. Just like I do
the silly

 /* Comment like this,
  * for multiple lines
  */

When I deal with the networking code. Because that's the preference for
the networking folks.

> I'd like to hear Linus take on this.

I doubt he cares about something this petty.

-- Steve