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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Mon, 14 Oct 2019 16:10:54 +0300
Message-ID: <CAHp75Vc1Tk7i1TCtT6RnfyBbt2F_skK8DEQ5iky1=spW06qsdQ@mail.gmail.com>
Subject: Re: [PATCH v4 1/1] printf: add support for printing symbolic error names
To:     Petr Mladek <pmladek@suse.com>
Cc:     Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= <uwe@kleine-koenig.org>,
        Joe Perches <joe@perches.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Oct 14, 2019 at 4:02 PM Petr Mladek <pmladek@suse.com> wrote:
> On Fri 2019-10-11 15:36:17, Rasmus Villemoes wrote:
> > It has been suggested several times to extend vsnprintf() to be able
> > to convert the numeric value of ENOSPC to print "ENOSPC". This
> > implements that as a %p extension: With %pe, one can do

> > +const char *errname(int err)
> > +{
> > +     bool pos = err > 0;
> > +     const char *name = __errname(err > 0 ? err : -err);
> > +
> > +     return name ? name + pos : NULL;
>
> This made me to check C standard. It seems that "true" really has
> to be "1".

You may guarantee it by using !!.

     return name ? name + !!(err > 0) : NULL;


But to me it seems like forgotten use of pos in the other case above.

Anyway, I would rather do

abs(err) in the first place

and simple use name + 1 in the second as you suggested with maybe a
comment that we skip E letter.

> But I think that I am not the only one who is not sure.
> I would prefer to make it less tricky and use, for example:
>
>         const char *name = __errname(err > 0 ? err : -err);
>         if (!name)
>                 return NULL;
>
>         return err > 0 ? name + 1 : name;

> > +}


-- 
With Best Regards,
Andy Shevchenko