linux-kernel - Re: [PATCH v9 7/8] xfs: support CoW in fsdax mode

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Date:   Thu, 16 Sep 2021 08:23:57 +0200
From:   Christoph Hellwig <hch@....de>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     djwong@...nel.org, hch@....de, linux-xfs@...r.kernel.org,
        dan.j.williams@...el.com, david@...morbit.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        nvdimm@...ts.linux.dev, rgoldwyn@...e.de, viro@...iv.linux.org.uk,
        willy@...radead.org
Subject: Re: [PATCH v9 7/8] xfs: support CoW in fsdax mode

On Wed, Sep 15, 2021 at 06:45:00PM +0800, Shiyang Ruan wrote:
> +static int
> +xfs_dax_write_iomap_end(
> +	struct inode 		*inode,
> +	loff_t 			pos,
> +	loff_t 			length,
> +	ssize_t 		written,
> +	unsigned 		flags,
> +	struct iomap 		*iomap)
> +{
> +	struct xfs_inode	*ip = XFS_I(inode);
> +	/*
> +	 * Usually we use @written to indicate whether the operation was
> +	 * successful.  But it is always positive or zero.  The CoW needs the
> +	 * actual error code from actor().  So, get it from
> +	 * iomap_iter->processed.
> +	 */
> +	const struct iomap_iter *iter =
> +				container_of(iomap, typeof(*iter), iomap);
> +
> +	if (!xfs_is_cow_inode(ip))
> +		return 0;
> +
> +	if (iter->processed <= 0) {
> +		xfs_reflink_cancel_cow_range(ip, pos, length, true);
> +		return 0;
> +	}
> +
> +	return xfs_reflink_end_cow(ip, pos, iter->processed);

Didn't we come to the conflusion last time that we don't actually
need to poke into the iomap_iter here as the written argument is equal
to iter->processed if it is > 0:

	if (iter->iomap.length && ops->iomap_end) {
		ret = ops->iomap_end(iter->inode, iter->pos, iomap_length(iter),
				iter->processed > 0 ? iter->processed : 0,
				iter->flags, &iter->iomap);
		..

So should be able to just do:

static int
xfs_dax_write_iomap_end(
	struct inode 		*inode,
	loff_t 			pos,
	loff_t 			length,
	ssize_t 		written,
	unsigned 		flags,
	struct iomap 		*iomap)
{
	struct xfs_inode	*ip = XFS_I(inode);

	if (!xfs_is_cow_inode(ip))
		return 0;

	if (!written) {
		xfs_reflink_cancel_cow_range(ip, pos, length, true);
		return 0;
	}

	return xfs_reflink_end_cow(ip, pos, written);
}