linux-kernel - Re: [PATCH 1/2 v2] tracing/events: provide string with undefined size support

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Date:	Fri, 17 Apr 2009 13:14:23 +0200
From:	Frédéric Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Zhaolei <zhaolei@...fujitsu.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2 v2] tracing/events: provide string with undefined size 
	support

2009/4/17 Steven Rostedt <rostedt@...dmis.org>:
>
> On Fri, 17 Apr 2009, Peter Zijlstra wrote:
>
>> On Fri, 2009-04-17 at 06:10 -0400, Steven Rostedt wrote:
>>
>> > When I replied to Frederic, I thought I could come up with a way to do
>> > something like you are proposing. Instead, I only ended up with the
>> > variant that Frederic implemented.
>> >
>> > I've done what you are suggesting several times in tracing. Logdev does
>> > this in its tracing.
>> >
>> > The problem that we have, is that we don't have actual code. We have a
>> > TRACE_EVENT macro that is doing the work for us. This, unfortunately,
>> > limits what we can do.
>>
>> Can't you do things like:
>>
>> #define __string(x) unsigned long length_##x, offset_##x;
>>
>>   TP_STRUCT__entry
>>
>>   size = sizeof(struct foo);
>>
>> #define __string(x) length_##x = strlen(x) + 1; size += length_##x;
>>
>>   TP_STRUCT__entry
>>
>>   entry = ring_buffer_lock_reserve(size);
>>   offset = sizeof(stuct foo);
>>
>> #define __string(x) \
>>       __entry->x = offset_##x = offset; offset += length_##x;
>>
>>   TP_STRUCT__entry
>>
>>   TP_fast_assign
>>
>> #define _string(x) strcpy(&entry->data[offset_##x], x);
>>
>>   TP_STRUCT__entry
>>
>>   ring_buffer_unlock();
>>
>> also, you don't need that __ending_string() thing, you can always end a
>> struct with char data[0], its 0 size ;-)
>>
>
> This looks very similar to what I suggested in the cross email.
>
> Frederic,
>
> You want to take a crack at implementing this. I think my description had
> a bit more details, but is basically the same as what Peter is describing
> here.
>
> I'd just make __string become an offset (as described in my email)
>
> Then the user could just index directly. They only need to worry about the
> print, the assignment would be automated.


Nice!
Ok, I will restart with it!


>
> -- Steve
>
>
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