linux-kernel - Re: ERR_PTR and PTR

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Message-ID: <Pine.LNX.4.64.1005162025560.12921@ask.diku.dk>
Date:	Sun, 16 May 2010 20:26:31 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: ERR_PTR and PTR_ERR

On Sun, 16 May 2010, Al Viro wrote:

> On Sun, May 16, 2010 at 11:05:23AM +0200, Julia Lawall wrote:
> > On Sun, 16 May 2010, Julia Lawall wrote:
> > 
> > > I see a number of occurrences of code like the following:
> > > 
> > >  	if (IS_ERR(alg))
> > > 		return ERR_PTR(PTR_ERR(alg));
> > > 
> > > Is there any reason why the second line couldn't just be return alg?
> > 
> > Hmm, never mind.  It seems to address a type problem.
> 
> More idiomatic way to deal with that is ERR_CAST(); see e.g. ext2_lookup() for
> use case:

Thanks.  That looks much nicer than ERR_PTR(PTR_ERR(alg)).

julia


> 	...
> 	inode = NULL;
> 	if (ino) {
> 		inode = ext2_iget(dir->i_sb, ino);
> 		if (unlikely(IS_ERR(inode))) {
> 			if (PTR_ERR(inode) == -ESTALE) {
> 				ext2_error(dir->i_sb, __func__,
> 						"deleted inode referenced: %lu",
> 						(unsigned long) ino);
> 				return ERR_PTR(-EIO);
> 			} else {
> 				return ERR_CAST(inode);
> 			}
> 		}
> 	}
> 	return d_splice_alias(inode, dentry);
> 
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