Re: [PATCH v7 7/8] fsdax: Introduce dax_iomap_ops for end of reflink

From: Christoph Hellwig <hch@lst.de>
To: Dan Williams <dan.j.williams@intel.com>
Cc: "ruansy.fnst" <ruansy.fnst@fujitsu.com>,
	"Darrick J. Wong" <djwong@kernel.org>,
	Christoph Hellwig <hch@lst.de>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	david <david@fromorbit.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux NVDIMM <nvdimm@lists.linux.dev>,
	Goldwyn Rodrigues <rgoldwyn@suse.de>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v7 7/8] fsdax: Introduce dax_iomap_ops for end of reflink
Date: Mon, 23 Aug 2021 15:02:48 +0200	[thread overview]
Message-ID: <20210823130248.GC15536@lst.de> (raw)
In-Reply-To: <CAPcyv4jM86gy-T5EEZf6M2m44v4MiGqYDhxisX59M5QJii6DVg@mail.gmail.com>

On Fri, Aug 20, 2021 at 08:18:44AM -0700, Dan Williams wrote:
> I notice that the @iomap argument to ->iomap_end() is reliably coming
> from @iter. So you could do the following in your iomap_end()
> callback:
> 
>         struct iomap_iter *iter = container_of(iomap, typeof(*iter), iomap);
>         struct xfs_inode *ip = XFS_I(inode);
>         ssize_t written = iter->processed;
>         bool cow = xfs_is_cow_inode(ip);
> 
>         if (cow) {
>                 if (written <= 0)
>                         xfs_reflink_cancel_cow_range(ip, pos, length, true)
>         }

I think this might be ok for now (with a big comment).  Willy's original
iomap iter series replaced the iomap_begin and iomap_end with a single
next callback that takes the iomap_iter, which would solve this issue.
My plan is to look into a series that implements this and sees if this
is indeed a net win.