linux-kernel - Re: [PATCH 27/39] union-mount: In-kernel copyup routines

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Date:	Fri, 7 May 2010 10:45:58 -0400
From:	Valerie Aurora <vaurora@...hat.com>
To:	Valdis.Kletnieks@...edu
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Jan Blunck <jblunck@...e.de>
Subject: Re: [PATCH 27/39] union-mount: In-kernel copyup routines

On Mon, May 03, 2010 at 09:40:04PM -0400, Valdis.Kletnieks@...edu wrote:
> On Mon, 03 May 2010 16:12:26 PDT, Valerie Aurora said:
> > When a file on the read-only layer of a union mount is altered, it
> > must be copied up to the topmost read-write layer.  This patch creates
> > union_copyup() and its supporting routines.
> > ---
> >  fs/union.c            |  244 +++++++++++++++++++++++++++++++++++++++++++++++
> 
> > +/**
> > + * union_copyup_data - Copy up len bytes of old's data to new
> > + *
> > + * @old: source file
> > + * @new: target file
> > + * @len: number of bytes to copy
> > + */
> > +
> > +static int union_copyup_data(struct path *old, struct vfsmount *new_mnt,
> > +			     struct dentry *new_dentry, size_t len)
> > +{
> > +	struct file *old_file;
> > +	struct file *new_file;
> > +	const struct cred *cred = current_cred();
> > +	loff_t offset = 0;
> > +	long bytes;
> > +	int error;
> 
> Should this be 'int error = 0;' ?
> 
> > +
> > +	if (len == 0)
> > +		return 0;
> > +
> > +	/* Get reference to balance later fput() */
> > +	path_get(old);
> > +	old_file = dentry_open(old->dentry, old->mnt, O_RDONLY, cred);
> > +	if (IS_ERR(old_file))
> > +		return PTR_ERR(old_file);
> > +
> > +	dget(new_dentry);
> > +	mntget(new_mnt);
> > +	new_file = dentry_open(new_dentry, new_mnt, O_WRONLY, cred);
> > +	if (IS_ERR(new_file)) {
> > +		error = PTR_ERR(new_file);
> > +		goto out_fput;
> > +	}
> > +
> > +	bytes = do_splice_direct(old_file, &offset, new_file, len,
> > +				 SPLICE_F_MOVE);
> > +	if (bytes < 0)
> > +		error = bytes;
> > +
> > +	fput(new_file);
> > +out_fput:
> > +	fput(old_file);
> > +	return error;
> > +}
> 
> because otherwise if do_splice_direct() returns a non-negative value,
> we can hit 'return error;' without ever having set error to anything?

Yes, I think you're right.  Thanks!

-VAL
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