linux-kernel - Re: [PATCH RFC] err.h: document that PTR_ERR should only be used if IS

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Date:   Tue, 16 Oct 2018 21:29:28 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Alessandro Rubini <rubini@...dd.com>, Michal.Vokac@...ft.com,
        corbet@....net, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, thierry.reding@...il.com,
        kernel@...gutronix.de, akpm@...ux-foundation.org
Subject: Re: [PATCH RFC] err.h: document that PTR_ERR should only be used if
 IS_ERR returns true

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-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |