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

[Shiyang Ruan]

On 2021/9/16 14:23, Christoph Hellwig wrote:
> 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);
> }

I see.  Thanks for your guidance.


--
Ruan