linux-kernel - Re: [RFC PATCH 2/5] tracing/events: nicer print format for parsing

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Date:	Tue, 9 Jun 2009 15:45:36 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Mel Gorman <mel@....ul.ie>,
	Christoph Hellwig <hch@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Peter Zijlstra <peterz@...radead.org>,
	Theodore Tso <tytso@....edu>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Zhaolei <zhaolei@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Jason Baron <jbaron@...hat.com>,
	Jiaying Zhang <jiayingz@...gle.com>
Subject: Re: [RFC PATCH 2/5] tracing/events: nicer print format for parsing

On Tue, 9 Jun 2009, Frederic Weisbecker wrote:
> 
>  
> > The language that is added by this patch is of the following:
> > 
> >  * FMT :=  constant string FMT | COMMAND FMT | empty
> >  * COMMAND := <TYPE:FIELD> | <mask:FIELD:DELIM:MASKS> | <sym:FIELD:SYMBOLS> |
> >  *               <if:FIELD:TRUE:FALSE>
> >  * TYPE := int | hex | ptr | string | strarray
> >  * FIELD := defined by the event structure
> >  * MASKS := MASK=NAME,MASKS | MASK=NAME
> >  * MASK := the bit mask to match
> >  * DELIM := delimiter to separate the fields. None and ':' are both allowed
> >  * SYMBOLS := SYM=NAME,SYMBOLS | SYM=NAME
> >  * SYM := the symbol value to test against
> >  * TRUE := print when field is non zero
> >  * FALSE := print when field is zero or NULL
> >  * NAME := the name to write when a match is found
> >  *
> >  * A '\<' would print '<'
> 
> 
> But I wonder if the above new language is not breaking the charm
> of the TRACE_EVENT(), which charm is that it's easy to implement (hopefully).
> 
> Everyone knows the printk formats. And I guess this new thing is easy and
> quick to learn. But because it's a new unknown language, the TRACE_EVENT
> will become less readable, less reachable for newcomers in TRACE_EVENT.

I tried to avoid this too, but when I started writing a tool in C that 
would parse the format file, I found that the printf was horrible.

Note, I will still keep the TP_printk() macro, that will not change. The 
new macro is TP_FORMAT() that preforms the tags. Thus, if you really want 
it to print out, you can use TP_printk, but the user space tools that read 
the binary will not know how to read it unless the printk is simple.

I really want to keep this language simple. If anyone has any better 
ideas, I'm all for it.

I barfed when I saw this in irq_handler_entry:

  print fmt: "irq=%d handler=%s", REC->irq, (char *)((void *)REC + REC->__data_loc_name)

That we probably can get to show something like:

  print fmt: "irq=%d handler=%s", REC->irq, __get_string(REC->name)

I plan on also adding some type tags. Perhaps adding a GFP that would do 
the flags for kmem, and have a way to export the values in another file.

But for now, I would like to add the tags "major" and "minor" that would 
get the major and minor from a device:

  <major:dev>  <minor:dev>

And also one that can handle time:

  <nsec2usec:nsec> that would convert a ns time to the "%lu.%03lu" format, 
or even a <nsec2sec:n:nsec> that would convert to "%lu.%0" n "lu" format.

Again, anyone have any better ideas?

-- Steve

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