Re: [PATCH v9] xfs: add FALLOC_FL_WRITE_ZEROES to XFS code base

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

On Mon, Feb 23, 2026 at 10:11:07AM +0100, Lukas Herbolt wrote:
> Add support for FALLOC_FL_WRITE_ZEROES if the underlying device enable
> the unmap write zeroes operation.
> 
> Signed-off-by: Lukas Herbolt <lukas@herbolt.com>
> ---
>  fs/xfs/xfs_bmap_util.c |  5 +++--
>  fs/xfs/xfs_bmap_util.h |  2 +-
>  fs/xfs/xfs_file.c      | 39 ++++++++++++++++++++++++++-------------
>  3 files changed, 30 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 2208a720ec3f..0c1b1fa82f8b 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -646,7 +646,8 @@ int
>  xfs_alloc_file_space(
>  	struct xfs_inode	*ip,
>  	xfs_off_t		offset,
> -	xfs_off_t		len)
> +	xfs_off_t		len,
> +	uint32_t		bmapi_flags)
>  {
>  	xfs_mount_t		*mp = ip->i_mount;
>  	xfs_off_t		count;
> @@ -748,7 +749,7 @@ xfs_alloc_file_space(
>  		 * will eventually reach the requested range.
>  		 */
>  		error = xfs_bmapi_write(tp, ip, startoffset_fsb,
> -				allocatesize_fsb, XFS_BMAPI_PREALLOC, 0, imapp,
> +				allocatesize_fsb, bmapi_flags, 0, imapp,
>  				&nimaps);
>  		if (error) {
>  			if (error != -ENOSR)
> diff --git a/fs/xfs/xfs_bmap_util.h b/fs/xfs/xfs_bmap_util.h
> index c477b3361630..2895cc97a572 100644
> --- a/fs/xfs/xfs_bmap_util.h
> +++ b/fs/xfs/xfs_bmap_util.h
> @@ -56,7 +56,7 @@ int	xfs_bmap_last_extent(struct xfs_trans *tp, struct xfs_inode *ip,
>  
>  /* preallocation and hole punch interface */
>  int	xfs_alloc_file_space(struct xfs_inode *ip, xfs_off_t offset,
> -		xfs_off_t len);
> +		xfs_off_t len, uint32_t bmapi_flags);
>  int	xfs_free_file_space(struct xfs_inode *ip, xfs_off_t offset,
>  		xfs_off_t len, struct xfs_zone_alloc_ctx *ac);
>  int	xfs_collapse_file_space(struct xfs_inode *, xfs_off_t offset,
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 7874cf745af3..83c45ada3cc8 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1293,6 +1293,7 @@ xfs_falloc_zero_range(
>  	unsigned int		blksize = i_blocksize(inode);
>  	loff_t			new_size = 0;
>  	int			error;
> +	uint32_t                bmapi_flags;
>  
>  	trace_xfs_zero_file_space(ip);
>  
> @@ -1300,18 +1301,27 @@ xfs_falloc_zero_range(
>  	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);

Where did this call to xfs_free_file_space go?  This looks like a
behavior change in the classic zero-range behavior.

--D

> -		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 (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;
> +		bmapi_flags = XFS_BMAPI_ZERO;
> +	} else {
> +		if (xfs_falloc_force_zero(ip, ac)) {
> +			error = xfs_zero_range(ip, offset, len, ac, NULL);
> +			goto set_filesize;
> +		}
> +		bmapi_flags = XFS_BMAPI_PREALLOC;
>  	}
> +
> +	len = round_up(offset + len, blksize) - round_down(offset, blksize);
> +	offset = round_down(offset, blksize);
> +
> +	error = xfs_alloc_file_space(ip, offset, len, bmapi_flags);
> +
> +set_filesize:
>  	if (error)
>  		return error;
>  	return xfs_falloc_setsize(file, new_size);
> @@ -1336,7 +1346,8 @@ xfs_falloc_unshare_range(
>  	if (error)
>  		return error;
>  
> -	error = xfs_alloc_file_space(XFS_I(inode), offset, len);
> +	error = xfs_alloc_file_space(XFS_I(inode), offset, len,
> +			XFS_BMAPI_PREALLOC);
>  	if (error)
>  		return error;
>  	return xfs_falloc_setsize(file, new_size);
> @@ -1364,7 +1375,8 @@ xfs_falloc_allocate_range(
>  	if (error)
>  		return error;
>  
> -	error = xfs_alloc_file_space(XFS_I(inode), offset, len);
> +	error = xfs_alloc_file_space(XFS_I(inode), offset, len,
> +			XFS_BMAPI_PREALLOC);
>  	if (error)
>  		return error;
>  	return xfs_falloc_setsize(file, new_size);
> @@ -1374,7 +1386,7 @@ 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(
> @@ -1417,6 +1429,7 @@ __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
> 
>