linux-kernel - Re: [PATCH tracing/kprobes v2 1/5] tracing/kprobes: Rename special variables syntax

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Date:	Tue, 06 Oct 2009 10:23:50 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	rostedt@...dmis.org
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [PATCH tracing/kprobes v2 1/5] tracing/kprobes: Rename special
 variables syntax

Steven Rostedt wrote:
> On Mon, 2009-10-05 at 21:26 +0200, Frederic Weisbecker wrote:
>> On Mon, Oct 05, 2009 at 12:59:01PM -0400, Masami Hiramatsu wrote:
>>> As far as I can see in arch/*/include/asm/ptrace.h, all registers start with
>>> alphabets :-). So, I'd like to suggest renaming sp-vars to '_sp-vars'.
>>>
>>> Then, we will have;
>>> - $local-vars
>>
>>
>> There is a risk of bash collision.
> 
> I actually prefer the "$" notation. As for bash collision, it is common
> for shell script writers to be able to distinguish a variable from bash.
> Yes we can backslash it, or quote it. But when I see a $var it sticks
> out to me that it is a variable. It's not hard to get around. For
> example, type:
> 
> $ echo "hello $DISPLAY"' or $DISPLAY'
> 
> and see what you get.
> 
> Makefiles and Perl use '$' for variables those that need to handle it
> with bash can easily cope with it.
> 
> So my vote is to keep the '$'. It is the most intuitive to what it
> means.
> 
> Just my 0.02€

OK, so here are syntax ideas

* current syntax
<Ftrace>
- $sp_var
- %regs
- @symbol
<Perf>
- local_var

* $local syntax
<Ftrace>
- sp_var
- %regs
- @symbol
<Perf>
- $local_var

* non $ syntax 1
<Ftrace>
- %sp_var
- %regs
- @symbol
<Perf>
- local_var

* non $ syntax 2
<Ftrace>
- %%sp_var or %@...var
- %regs
- @symbol
<Perf>
- local_var

So, which one do you like to use? :-)

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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