Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 16 Oct 2018 21:29:28 +0200
From:   Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>
To:     Al Viro <viro@ZenIV.linux.org.uk>
Cc:     Alessandro Rubini <rubini@gnudd.com>, Michal.Vokac@ysoft.com,
        corbet@lwn.net, gregkh@linuxfoundation.org,
        linux-kernel@vger.kernel.org, thierry.reding@gmail.com,
        kernel@pengutronix.de, akpm@linux-foundation.org
Subject: Re: [PATCH RFC] err.h: document that PTR_ERR should only be used if
 IS_ERR returns true
Message-ID: <20181016192928.pinjwxfors4reigh@pengutronix.de>
References: <20181014202807.16412-1-uwe@kleine-koenig.org>
 <20181015093708.GA22876@mail.gnudd.com>
 <20181016180650.GZ32577@ZenIV.linux.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20181016180650.GZ32577@ZenIV.linux.org.uk>
User-Agent: NeoMutt/20170113 (1.7.2)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Oct 16, 2018 at 07:06:51PM +0100, Al Viro wrote:
> On Mon, Oct 15, 2018 at 11:37:08AM +0200, Alessandro Rubini wrote:
> 
> > OTOH I admit you can compare any value with -EINVAL, after PTR_ERR.
> > But in general you first detect the error condition and then split
> > among error (or print a message according to the exact value.
> 
> 	if (IS_ERR(p) && PTR_ERR(p) == -ENOENT)
> instead of
> 	if (p == ERR_PTR(-ENOENT))
> 
> is ugly, obfuscating what's going on for no good reason and I'm going
> to keep killing those every time I run into one...

And what do you do if you see a

	p = somefunc(...);
	if (PTR_ERR(p) == -ENOENT)

without first checking for IS_ERR(p)? Another alternative is

	if (PTR_ERR_OR_ZERO(p) == -ENOENT)

? In your eyes, should they all be converted to

	if (p == ERR_PTR(-ENOENT))

?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |