linux-kernel - Re: [PATCH v7 7/8] fsdax: Introduce dax_iomap

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Date:   Thu, 19 Aug 2021 20:01:08 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     "Darrick J. Wong" <djwong@...nel.org>,
        Christoph Hellwig <hch@....de>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        david <david@...morbit.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v7 7/8] fsdax: Introduce dax_iomap_ops for end of reflink

On Sun, Aug 15, 2021 at 11:05 PM Shiyang Ruan <ruansy.fnst@...itsu.com> wrote:
>
> After writing data, reflink requires end operations to remap those new
> allocated extents.  The current ->iomap_end() ignores the error code
> returned from ->actor(), so we introduce this dax_iomap_ops and change
> the dax_iomap_*() interfaces to do this job.
>
> - the dax_iomap_ops contains the original struct iomap_ops and fsdax
>     specific ->actor_end(), which is for the end operations of reflink
> - also introduce dax specific zero_range, truncate_page
> - create new dax_iomap_ops for ext2 and ext4
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@...itsu.com>
> ---
>  fs/dax.c               | 68 +++++++++++++++++++++++++++++++++++++-----
>  fs/ext2/ext2.h         |  3 ++
>  fs/ext2/file.c         |  6 ++--
>  fs/ext2/inode.c        | 11 +++++--
>  fs/ext4/ext4.h         |  3 ++
>  fs/ext4/file.c         |  6 ++--
>  fs/ext4/inode.c        | 13 ++++++--
>  fs/iomap/buffered-io.c |  3 +-
>  fs/xfs/xfs_bmap_util.c |  3 +-
>  fs/xfs/xfs_file.c      |  8 ++---
>  fs/xfs/xfs_iomap.c     | 36 +++++++++++++++++++++-
>  fs/xfs/xfs_iomap.h     | 33 ++++++++++++++++++++
>  fs/xfs/xfs_iops.c      |  7 ++---
>  fs/xfs/xfs_reflink.c   |  3 +-
>  include/linux/dax.h    | 21 ++++++++++---
>  include/linux/iomap.h  |  1 +
>  16 files changed, 189 insertions(+), 36 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 74dd918cff1f..0e0536765a7e 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1348,11 +1348,30 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
>         return done ? done : ret;
>  }
>
> +static inline int
> +__dax_iomap_iter(struct iomap_iter *iter, const struct dax_iomap_ops *ops)
> +{
> +       int ret;
> +
> +       /*
> +        * Call dax_iomap_ops->actor_end() before iomap_ops->iomap_end() in
> +        * each iteration.
> +        */
> +       if (iter->iomap.length && ops->actor_end) {
> +               ret = ops->actor_end(iter->inode, iter->pos, iter->len,
> +                                    iter->processed);
> +               if (ret < 0)
> +                       return ret;
> +       }
> +
> +       return iomap_iter(iter, &ops->iomap_ops);

This reorganization looks needlessly noisy. Why not require the
iomap_end operation to perform the actor_end work. I.e. why can't
xfs_dax_write_iomap_actor_end() just be the passed in iomap_end? I am
not seeing where the ->iomap_end() result is ignored?