From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v5 bpf-next 06/10] tracepoint: compute num_args at build
 time
Date: Mon, 26 Mar 2018 14:11:04 -0400
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To: Alexei Starovoitov <ast@fb.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, "David S. Miller" <davem@davemloft.net>, Daniel Borkmann <daniel@iogearbox.net>, Linus Torvalds <torvalds@linux-foundation.org>, Peter Zijlstra <peterz@infradead.org>, netdev <netdev@vger.kernel.org>, kernel-team <kernel-team@fb.com>, linux-api <linux-api@vger.kernel.org>, "Frank Ch. Eigler" <fche@redhat.com>
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On Mon, 26 Mar 2018 10:55:51 -0700
Alexei Starovoitov <ast@fb.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.


> One thing is to be nice to out-of-tree and do not break them
> for no reason, but arguing that kernel shouldn't add a minor extension
> to for_each_kernel_tracepoint() api is really taking the whole thing
> to next level.

That's not the point. I disagree with the reason for the change, and
believe that it would be cleaner to add a find_by_name() function.
Which would make your patch set even cleaner. 

Instead of having in the bpf code:

static void *__find_tp(struct tracepoint *tp, void *priv)
{
	char *name = priv;

	if (!strcmp(tp->name, name))
		return tp;
	return NULL;
}

[..]

	tp = for_each_kernel_tracepoint(__find_tp, tp_name);
	if (!tp)
		return -ENOENT;


You would simply have:

	tp = tracepoint_find_by_name(tp_name);
	if (!tp)
		return -ENOENT;

That would make the code more obvious to what it is doing. And this
does not impede your patch set at all.

-- Steve