Re: [PATCH v8 4/7] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero

[Christoph Hellwig <hch@lst.de>]

On Sun, Aug 29, 2021 at 08:25:14PM +0800, Shiyang Ruan wrote:
> Punch hole on a reflinked file needs dax_iomap_cow_copy() too.
> Otherwise, data in not aligned area will be not correct.  So, add the
> srcmap to dax_iomap_zero() and replace memset() as dax_iomap_cow_copy().
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  fs/dax.c               | 26 ++++++++++++++++----------
>  fs/iomap/buffered-io.c |  4 ++--
>  include/linux/dax.h    |  3 ++-
>  3 files changed, 20 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index f4acb79cb811..b294900e574e 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1209,7 +1209,8 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
>  }
>  #endif /* CONFIG_FS_DAX_PMD */
>  
> -s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
> +s64 dax_iomap_zero(loff_t pos, u64 length, const struct iomap *iomap,
> +		const struct iomap *srcmap)

We can in fact pass the iomap_iter here as well.  (probably as a prep
patch).

>  	if (page_aligned)
>  		rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
> -	else
> +	else {
>  		rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);

I'd clean this up a bit by doing:

	id = dax_read_lock();	
	if (page_aligned) {
		rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
		goto out;
	}

	// non aligned case here without extra indentation or checks