linux-kernel - Re: [PATCH 5/7] fsdax: Dedup file range to use a compare function

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Date:   Mon, 8 Feb 2021 16:19:20 +0100
From:   Christoph Hellwig <hch@....de>
To:     Shiyang Ruan <ruansy.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
        darrick.wong@...cle.com, dan.j.williams@...el.com,
        willy@...radead.org, jack@...e.cz, viro@...iv.linux.org.uk,
        linux-btrfs@...r.kernel.org, ocfs2-devel@....oracle.com,
        david@...morbit.com, hch@....de, rgoldwyn@...e.de,
        Goldwyn Rodrigues <rgoldwyn@...e.com>
Subject: Re: [PATCH 5/7] fsdax: Dedup file range to use a compare function

On Mon, Feb 08, 2021 at 01:09:22AM +0800, Shiyang Ruan wrote:
> With dax we cannot deal with readpage() etc. So, we create a
> funciton callback to perform the file data comparison and pass

s/funciton/function/g

> +#define MIN(a, b) (((a) < (b)) ? (a) : (b))

This should use the existing min or min_t helpers.


>  int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
>  				  struct file *file_out, loff_t pos_out,
> -				  loff_t *len, unsigned int remap_flags)
> +				  loff_t *len, unsigned int remap_flags,
> +				  compare_range_t compare_range_fn)

Can we keep generic_remap_file_range_prep as-is, and add a new
dax_remap_file_range_prep, both sharing a low-level
__generic_remap_file_range_prep implementation?  And for that
implementation I'd also go for classic if/else instead of the function
pointer.

> +extern int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
> +					 struct inode *dest, loff_t destoff,
> +					 loff_t len, bool *is_same);

no need for the extern.