linux-kernel - Re: [RFC v2 2/2] docs: ftrace: Fix typos

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Message-ID: <20191125234957.nwbzz72aarbhdni2@ubuntu1804-desktop>
Date:   Mon, 25 Nov 2019 18:49:57 -0500
From:   "Frank A. Cancio Bello" <frank@...eralsoftwareinc.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        joel@...lfernandes.org, saiprakash.ranjan@...eaurora.org
Subject: Re: [RFC v2 2/2] docs: ftrace: Fix typos

On Mon, Nov 25, 2019 at 04:46:25PM -0500, Steven Rostedt wrote:
> On Mon, 25 Nov 2019 12:37:09 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Sun, 24 Nov 2019 23:38:41 -0500
> > "Frank A. Cancio Bello" <frank@...eralsoftwareinc.com> wrote:
> > 
> > > --- a/Documentation/trace/ring-buffer-design.txt
> > > +++ b/Documentation/trace/ring-buffer-design.txt
> > > @@ -37,7 +37,7 @@ commit_page - a pointer to the page with the last finished non-nested write.
> > >  
> > >  cmpxchg - hardware-assisted atomic transaction that performs the following:
> > >  
> > > -   A = B iff previous A == C
> > > +   A = B if previous A == C  
> > 
> > This wasn't a typo. "iff" means "if and only if" which is a standard
> > notation. That is, this is shorthand for:
> > 
> >   A = B if previous A == C
> >   previous A == C if A = B
> 
> Although thinking about this more, this may not be correct. If
> previous A == B, then A = B, thus the "iff" notation is not actually
> accurate.
> 
> This wouldn't then be a typo fix, but a real fix to the logic ;-)
> 

What are the odds ;)

I knew about the concept https://en.wikipedia.org/wiki/If_and_only_if
from school math but didn't remember the notation. For me was
suspicious so, I  looked in "the cmpxchg doc" and nothing referring
to "iff" was there, then I decided to classified it as a typo.

Now thinking more deeply, I agreed with you that was not a typo but
a "logic mistake", even not for the same reason ;)

Being not 100% sure of what I'm about to say, I will say it
anyway because you have been kind enough to write the second email.

"if and only if (shortened as iff) is a biconditional logical
connective between statements" and A = B can't be considered a
logical statement in the context of that definition (math/logic),
even it could be in C.

Thank you Steven one more time for such a quick reply!
frank a.