linux-kernel - Re: [PATCH v5 3/7] fsdax: Add dax_iomap_cow_copy() for dax_iomap

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Date:   Tue, 11 May 2021 18:17:38 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Shiyang Ruan <ruansy.fnst@...itsu.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, viro@...iv.linux.org.uk, david@...morbit.com,
        hch@....de, rgoldwyn@...e.de,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: Re: [PATCH v5 3/7] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero

On Tue, May 11, 2021 at 11:09:29AM +0800, Shiyang Ruan wrote:
> Punch hole on a reflinked file needs dax_copy_edge() too.  Otherwise,
> data in not aligned area will be not correct.  So, add the srcmap to
> dax_iomap_zero() and replace memset() as dax_copy_edge().
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@...itsu.com>
> Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> ---
>  fs/dax.c               | 25 +++++++++++++++----------
>  fs/iomap/buffered-io.c |  2 +-
>  include/linux/dax.h    |  3 ++-
>  3 files changed, 18 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index ef0e564e7904..ee9d28a79bfb 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1186,7 +1186,8 @@ 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, struct iomap *iomap,
> +		struct iomap *srcmap)
>  {
>  	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
>  	pgoff_t pgoff;
> @@ -1208,19 +1209,23 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
>  
>  	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);
> -	if (rc < 0) {
> -		dax_read_unlock(id);
> -		return rc;
> -	}
> -
> -	if (!page_aligned) {
> -		memset(kaddr + offset, 0, size);
> +		if (rc < 0)
> +			goto out;
> +		if (iomap->addr != srcmap->addr) {

Why isn't this "if (srcmap->type != IOMAP_HOLE)" ?

I suppose it has the same effect, since @iomap should never be a hole
and we should never have a @srcmap that's the same as @iomap, but
still, we use IOMAP_HOLE checks in most other parts of fs/iomap/.

Other than that, the logic looks decent to me.

--D

> +			rc = dax_iomap_cow_copy(offset, size, PAGE_SIZE, srcmap,
> +						kaddr);
> +			if (rc < 0)
> +				goto out;
> +		} else
> +			memset(kaddr + offset, 0, size);
>  		dax_flush(iomap->dax_dev, kaddr + offset, size);
>  	}
> +
> +out:
>  	dax_read_unlock(id);
> -	return size;
> +	return rc < 0 ? rc : size;
>  }
>  
>  static loff_t
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index f2cd2034a87b..2734955ea67f 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -933,7 +933,7 @@ static loff_t iomap_zero_range_actor(struct inode *inode, loff_t pos,
>  		s64 bytes;
>  
>  		if (IS_DAX(inode))
> -			bytes = dax_iomap_zero(pos, length, iomap);
> +			bytes = dax_iomap_zero(pos, length, iomap, srcmap);
>  		else
>  			bytes = iomap_zero(inode, pos, length, iomap, srcmap);
>  		if (bytes < 0)
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b52f084aa643..3275e01ed33d 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -237,7 +237,8 @@ vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
>  int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index);
>  int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
>  				      pgoff_t index);
> -s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap);
> +s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap,
> +		struct iomap *srcmap);
>  static inline bool dax_mapping(struct address_space *mapping)
>  {
>  	return mapping->host && IS_DAX(mapping->host);
> -- 
> 2.31.1
> 
> 
>