linux-kernel - Re: [PATCH 1/2] tracing/events: clean up for ftrace_set_clr

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Date:	Fri, 8 May 2009 13:47:45 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Li Zefan <lizf@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] tracing/events: clean up for ftrace_set_clr_event()

On Fri, May 08, 2009 at 07:35:22AM -0400, Steven Rostedt wrote:
> 
> On Fri, 8 May 2009, Frederic Weisbecker wrote:
> > >  
> > > -static int ftrace_set_clr_event(char *buf, int set)
> > > +/*
> > > + * __ftrace_set_clr_event(NULL, NULL, NULL, set) will set/unset all events.
> > > + */
> > > +static int __ftrace_set_clr_event(const char *match, const char *sub,
> > > +				  const char *event, int set)
> > >  {
> > >  	struct ftrace_event_call *call;
> > > +	int ret;
> > > +
> > > +	mutex_lock(&event_mutex);
> > > +	list_for_each_entry(call, &ftrace_events, list) {
> > > +
> > > +		if (!call->name || !call->regfunc)
> > > +			continue;
> > > +
> > > +		if (match &&
> > > +		    strcmp(match, call->name) != 0 &&
> > > +		    strcmp(match, call->system) != 0)
> > > +			continue;
> > > +
> > > +		if (sub && strcmp(sub, call->system) != 0)
> > > +			continue;
> > > +
> > > +		if (event && strcmp(event, call->name) != 0)
> > > +			continue;
> > 
> > 
> > Neat: You can simply use !strcmp(...)
> 
> Hehe, no he can't. It would be "strcmp(...)" for the true case. This is 
> exactly why I prefer to use "strcmp(...) != 0" over "!strcmp(...)". 
> Because, like you, I've confused "!strcmp(...)" too many times as "not a 
> match" when it in fact means "is a match".
> 
> I've made this mistake enough that I've given up on using just "strcmp" or 
> "!strcmp". "strcmp() != 0" and "strcmp() == 0" show what you want much 
> better.
> 

You're right. It provides a good disambiguation.
The C philosophy has this 0 == SUCCESS convention which doesn't match
the human brain logic that expect 0 is a false and 1 is a true....

I guess that's because "!" provides quick checks about non-failures
and detailed errors can then fit in custom values. But still, I guess
we all stuck in this scheme, at least in a last remaining nerve cell
which says "hell, but look! wtf...", though this poor neurone ends
up being punched and kicked by the rest of the brain folks...


Frederic.

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