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

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Message-ID: <20191125164625.01101109@gandalf.local.home>
Date:   Mon, 25 Nov 2019 16:46:25 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Frank A. Cancio Bello" <frank@...eralsoftwareinc.com>
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, 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 ;-)

-- Steve

> 
> 
> >  
> >     R = cmpxchg(A, C, B) is saying that we replace A with B if and only if
> >        current A is equal to C, and we put the old (current) A into R
> > --