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

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Message-ID: <20090413034531.GC11652@elte.hu>
Date:	Mon, 13 Apr 2009 05:45:32 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Frederic Weisbecker <fweisbec@...il.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


* Li Zefan <lizf@...fujitsu.com> wrote:

> > 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.

Yeah, good point. I think we should avoid such field name aliasing. 
Even without the filter assignment ambiguity problem it would be 
confusing to users to have two same-name but different-type fields 
in two separate events.

	Ingo
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