linux-kernel - Re: [PATCH 4/7] tracing/filters: allow user to specify a filter val to be string

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Date:	Sun, 12 Apr 2009 12:04:50 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Li Zefan <lizf@...fujitsu.com>, Tom Zanussi <tzanussi@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] tracing/filters: allow user to specify a filter
	val to be string


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> Hi Li,
> 
> On Sat, Apr 11, 2009 at 03:53:05PM +0800, Li Zefan wrote:
> > Suppose we would like to trace all tasks named '123', but this
> > will fail:
> >  # echo 'parent_comm == 123' > events/sched/sched_process_fork/filter
> >  bash: echo: write error: Invalid argument
> > 
> > With this patch, we allow it by:
> >  # echo 'parent_comm == \123' > events/sched/sched_process_fork/filter
> >  # cat events/sched/sched_process_fork/filter
> >  parent_comm == 123
> 
> Well, IMHO, it would be rather better to just echo 
> 'parent_comm == 123' and let it answer depending of which 
> filter_pred_*() callback we have for the concerned field.
>
> 
> The culprit is this part in filter_parse():
> 
> pred->val = simple_strtoull(val_str, &tmp, 10);
> if (tmp == val_str) {
> 	pred->str_val = kstrdup(val_str, GFP_KERNEL);
> 	if (!pred->str_val)
> 		return -ENOMEM;
> }
> 
> The idea would be to not anymore base the check on simple_strtoull to
> guess whether this is a number or a string, making it act subsequently
> to this assumption, which is not the good assumption we must base our
> parsing yet.
> 
> Instead, we could let filter_parse only do the job of extracting the tokens
> and then fill the whole pred struct without yet bothering about the type
> of the value.
> 
> Thereafter we may defer the real value type checking on filter_add_pred()
> depending on the type of the concerned field:
> 
> if (is_string_field()) {
> 	add it as a string value;
> } else {
> 	do the check with simple_strtoull
> 	looks good? Then go to the number size switch....
> 	...
> }
> 
> You see?
> 
> I think it would be a saner basis of parsing.

Agreed. The user input itself is unambigously parse-able - 
and we should not work around parsing limitations by 
complicating the user input.

The failure situation that Li found should obviously be 
fixed.

	Ingo
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