linux-kernel - Re: ERR_PTR and PTR

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Message-ID: <20100516173729.GE31073@ZenIV.linux.org.uk>
Date:	Sun, 16 May 2010 18:37:29 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Julia Lawall <julia@...u.dk>
Cc:	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: ERR_PTR and PTR_ERR

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:
	...
	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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