Re: [PATCH v11 2/2] xfs: add FALLOC_FL_WRITE_ZEROES to XFS code base

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Mar 09, 2026 at 07:12:36PM +0100, Lukas Herbolt wrote:
> Add support for FALLOC_FL_WRITE_ZEROES if the underlying device
> enable the unmap write zeroes operation.
> 
> Co-developed-by: Pankaj Raghav <p.raghav@samsung.com>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> Signed-off-by: Lukas Herbolt <lukas@herbolt.com>
> 
> ---
>  v11 changes:
> 	- split into 2 patches separating the bmapi_flags addition
> 	- 2 step allocation, to avoid zeroing beyond EOF
> 
>  fs/xfs/xfs_file.c | 41 +++++++++++++++++++++++++++++------------
>  1 file changed, 29 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index fd049a1fc9c6..f8c1611e3267 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1293,29 +1293,45 @@ xfs_falloc_zero_range(
>  	unsigned int		blksize = i_blocksize(inode);
>  	loff_t			new_size = 0;
>  	int			error;
> +	bool                    need_convert = false;
>  
>  	trace_xfs_zero_file_space(ip);
>  
> +	if (mode & FALLOC_FL_WRITE_ZEROES) {
> +		if (xfs_is_always_cow_inode(ip) ||
> +		    !bdev_write_zeroes_unmap_sectors(
> +			    xfs_inode_buftarg(ip)->bt_bdev))
> +			return -EOPNOTSUPP;
> +		need_convert = true;
> +	}
> +
>  	error = xfs_falloc_newsize(file, mode, offset, len, &new_size);
>  	if (error)
>  		return error;
>  
>  	if (xfs_falloc_force_zero(ip, ac)) {
>  		error = xfs_zero_range(ip, offset, len, ac, NULL);
> -	} else {
> -		error = xfs_free_file_space(ip, offset, len, ac);
> -		if (error)
> -			return error;
> -
> -		len = round_up(offset + len, blksize) -
> -			round_down(offset, blksize);
> -		offset = round_down(offset, blksize);
> -		error = xfs_alloc_file_space(ip, offset, len,
> -				XFS_BMAPI_PREALLOC);
> +		goto set_filesize;
>  	}
> +	error = xfs_free_file_space(ip, offset, len, ac);
>  	if (error)
>  		return error;
> -	return xfs_falloc_setsize(file, new_size);
> +
> +	len = round_up(offset + len, blksize) - round_down(offset, blksize);
> +	offset = round_down(offset, blksize);
> +	error = xfs_alloc_file_space(ip, offset, len, XFS_BMAPI_PREALLOC);
> +
> +set_filesize:
> +	if (error)
> +		return error;
> +
> +	error = xfs_falloc_setsize(file, new_size);
> +	if (error)
> +		return error;
> +	if (need_convert)
> +		error = xfs_alloc_file_space(ip, offset, len,
> +				XFS_BMAPI_CONVERT | XFS_BMAPI_ZERO);
> +	return error;
>  }

I can't help but think this would be cleaner as:

static int
xfs_falloc_write_zero_range(
	struct file		*file,
	int			mode,
	loff_t			offset,
	loff_t			len,
	struct xfs_zone_alloc_ctx *ac)
{
	struct inode		*inode = file_inode(file);
	struct xfs_inode	*ip = XFS_I(inode);
	unsigned int		blksize = i_blocksize(inode);
	loff_t			new_size = 0;
	int			error;

	trace_xfs_zero_file_space(ip);

	if (xfs_is_always_cow_inode(ip) ||
	    !bdev_write_zeroes_unmap_sectors(
				xfs_inode_buftarg(ip)->bt_bdev))
		return -EOPNOTSUPP;

	error = xfs_falloc_newsize(file, mode, offset, len, &new_size);
	if (error)
		return error;

	if (xfs_falloc_force_zero(ip, ac)) {
		error = xfs_zero_range(ip, offset, len, ac, NULL);
		if (error)
			return error;

		return xfs_falloc_setsize(file, new_size);
	}

	error = xfs_free_file_space(ip, offset, len, ac);
	if (error)
		return error;

	len = round_up(offset + len, blksize) -
		round_down(offset, blksize);
	offset = round_down(offset, blksize);
	error = xfs_alloc_file_space(ip, offset, len);
	if (error)
		return error;

	error = xfs_falloc_setsize(file, new_size);
	if (error)
		return error;

	return xfs_alloc_file_space(ip, offset, len,
			XFS_BMAPI_CONVERT | XFS_BMAPI_ZERO);
}

...assuming there's even a point to WRITE_ZEROES on a zoned file?

--D

>>   
>  static int
> @@ -1377,7 +1393,7 @@ xfs_falloc_allocate_range(
>  		(FALLOC_FL_ALLOCATE_RANGE | FALLOC_FL_KEEP_SIZE |	\
>  		 FALLOC_FL_PUNCH_HOLE |	FALLOC_FL_COLLAPSE_RANGE |	\
>  		 FALLOC_FL_ZERO_RANGE |	FALLOC_FL_INSERT_RANGE |	\
> -		 FALLOC_FL_UNSHARE_RANGE)
> +		 FALLOC_FL_UNSHARE_RANGE | FALLOC_FL_WRITE_ZEROES)
>  
>  STATIC long
>  __xfs_file_fallocate(
> @@ -1420,6 +1436,7 @@ __xfs_file_fallocate(
>  	case FALLOC_FL_INSERT_RANGE:
>  		error = xfs_falloc_insert_range(file, offset, len);
>  		break;
> +	case FALLOC_FL_WRITE_ZEROES:
>  	case FALLOC_FL_ZERO_RANGE:
>  		error = xfs_falloc_zero_range(file, mode, offset, len, ac);
>  		break;
> -- 
> 2.53.0
> 
>