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

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Date:	Mon, 03 May 2010 21:40:04 -0400
From:	Valdis.Kletnieks@...edu
To:	Valerie Aurora <vaurora@...hat.com>
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, 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?


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