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

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Message-ID: <49E2974D.6080105@cn.fujitsu.com>
Date:	Mon, 13 Apr 2009 09:37:17 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, 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

> 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?
> 

Right! Actually I thought about this, then I found one issue, suppose event
foo and event bar both have a field named fb but one is string and one is
integer. Now do this:
  # echo 'fb == 123' > events/foo-bar/filter

This will set both filters, but not only the integer one.

But now I think this hardly happen in real-life, and it's not a big issue
if it does happen. So I agree with you on this issue.

Thanks.

> I think it would be a saner basis of parsing.
> 
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