linux-kernel - Re: [PATCH 2/2] tracing/filters: remove error messages

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Message-ID: <4A39958C.4010801@cn.fujitsu.com>
Date:	Thu, 18 Jun 2009 09:17:00 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	Tom Zanussi <tzanussi@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] tracing/filters: remove error messages

Frederic Weisbecker wrote:
> On Wed, Jun 17, 2009 at 04:47:15PM +0800, Li Zefan wrote:
>> Now we restore original filter is the new one can't be applied,
>> and no long show error messages, so we can remove them totally.
> 
> Why?
> These messages are very powerful to point a user to its mistakes
> in filters syntaxes or semantics.
> 
> I really think we are removing a very useful feature in this patch.
> 

I think it's better done by providing a user-space program/script.

So what's the criterion to decide what should be in kernel and
what should be in user-space?

btw, this feature is not full-fledged, that it can't point to the
exact position where error occured, and the implementation will add
complexity and I'm sure it's worthy or not.

> May be we can keep the previous filter in case of new filter string
> inserting failure, though if the user wanted to insert a new one, there
> are few chances that the previous one is still relevant for him.
> I don't know.
> 
>> Another reason is, I don't think it's good to show error messages
>> when reading a control file.
> 
> So, why not create a filter_error file in this case? One for each
> event and subsys that would print the last error?
> 

Yeah, if we do want to keep this feature in the kernel.
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