Re: [PATCH v3 07/10] iomap: Introduce iomap_apply2() for operations on two files

From: Ritesh Harjani <ritesh.list@gmail.com>
To: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc: linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org,
	darrick.wong@oracle.com, willy@infradead.org, jack@suse.cz,
	viro@zeniv.linux.org.uk, linux-btrfs@vger.kernel.org,
	ocfs2-devel@oss.oracle.com, david@fromorbit.com, hch@lst.de,
	rgoldwyn@suse.de
Subject: Re: [PATCH v3 07/10] iomap: Introduce iomap_apply2() for operations on two files
Date: Thu, 1 Apr 2021 12:42:30 +0530	[thread overview]
Message-ID: <20210401071230.wbrawpzk3opzmntv@riteshh-domain> (raw)
In-Reply-To: <20210319015237.993880-8-ruansy.fnst@fujitsu.com>

On 21/03/19 09:52AM, Shiyang Ruan wrote:
> Some operations, such as comparing a range of data in two files under
> fsdax mode, requires nested iomap_open()/iomap_end() on two file.  Thus,
> we introduce iomap_apply2() to accept arguments from two files and
> iomap_actor2_t for actions on two files.
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> ---
>  fs/iomap/apply.c      | 56 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/iomap.h |  7 +++++-
>  2 files changed, 62 insertions(+), 1 deletion(-)
>
> diff --git a/fs/iomap/apply.c b/fs/iomap/apply.c
> index 26ab6563181f..fbc38ce3d5b6 100644
> --- a/fs/iomap/apply.c
> +++ b/fs/iomap/apply.c
> @@ -97,3 +97,59 @@ iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
>
>  	return written ? written : ret;
>  }
> +
> +loff_t
> +iomap_apply2(struct inode *ino1, loff_t pos1, struct inode *ino2, loff_t pos2,
> +		loff_t length, unsigned int flags, const struct iomap_ops *ops,
> +		void *data, iomap_actor2_t actor)
> +{
> +	struct iomap smap = { .type = IOMAP_HOLE };
> +	struct iomap dmap = { .type = IOMAP_HOLE };
> +	loff_t written = 0, ret, ret2 = 0;
> +	loff_t len1 = length, len2, min_len;
> +
> +	ret = ops->iomap_begin(ino1, pos1, len1, flags, &smap, NULL);
> +	if (ret)
> +		goto out_src;

if above call fails we need not call ->iomap_end() on smap.

> +	if (WARN_ON(smap.offset > pos1)) {
> +		written = -EIO;
> +		goto out_src;
> +	}
> +	if (WARN_ON(smap.length == 0)) {
> +		written = -EIO;
> +		goto out_src;
> +	}
> +	len2 = min_t(loff_t, len1, smap.length);
> +
> +	ret = ops->iomap_begin(ino2, pos2, len2, flags, &dmap, NULL);
> +	if (ret)
> +		goto out_dest;

ditto

> +	if (WARN_ON(dmap.offset > pos2)) {
> +		written = -EIO;
> +		goto out_dest;
> +	}
> +	if (WARN_ON(dmap.length == 0)) {
> +		written = -EIO;
> +		goto out_dest;
> +	}
> +	min_len = min_t(loff_t, len2, dmap.length);
> +
> +	written = actor(ino1, pos1, ino2, pos2, min_len, data, &smap, &dmap);
> +
> +out_dest:
> +	if (ops->iomap_end)
> +		ret2 = ops->iomap_end(ino2, pos2, len2,
> +				      written > 0 ? written : 0, flags, &dmap);
> +out_src:
> +	if (ops->iomap_end)
> +		ret = ops->iomap_end(ino1, pos1, len1,
> +				     written > 0 ? written : 0, flags, &smap);
> +

I guess, this maynot be a problem, but I still think we should be
consistent w.r.t len argument we are passing in ->iomap_end() for both type of
iomap_apply* family of functions.
IIUC, we used to call ->iomap_end() with the length argument filled by the
filesystem from ->iomap_begin() call.

whereas above breaks that behavior. Although I don't think this is FATAL, but
still it is better to be consistent with the APIs.
Thoughts?

> +	if (ret)
> +		return written ? written : ret;
> +
> +	if (ret2)
> +		return written ? written : ret2;
> +
> +	return written;
> +}

	if (written)
		return written;

	return ret ? ret : ret2;

Is above a simpler version?

-ritesh
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