Re: [PATCH xfsprogs v2] xfs_io: add FALLOC_FL_WRITE_ZEROES support

[Darrick J. Wong]

On Wed, Aug 13, 2025 at 10:42:50AM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> 
> The Linux kernel (since version 6.17) supports FALLOC_FL_WRITE_ZEROES in
> fallocate(2). Add support for FALLOC_FL_WRITE_ZEROES support to the
> fallocate utility by introducing a new 'fwzero' command in the xfs_io
> tool.
> 
> Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=278c7d9b5e0c
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
> ---
> v1->v2:
>  - Minor description modification to align with the kernel.
> 
>  io/prealloc.c     | 36 ++++++++++++++++++++++++++++++++++++
>  man/man8/xfs_io.8 |  6 ++++++
>  2 files changed, 42 insertions(+)
> 
> diff --git a/io/prealloc.c b/io/prealloc.c
> index 8e968c9f..9a64bf53 100644
> --- a/io/prealloc.c
> +++ b/io/prealloc.c
> @@ -30,6 +30,10 @@
>  #define FALLOC_FL_UNSHARE_RANGE 0x40
>  #endif
>  
> +#ifndef FALLOC_FL_WRITE_ZEROES
> +#define FALLOC_FL_WRITE_ZEROES 0x80
> +#endif
> +
>  static cmdinfo_t allocsp_cmd;
>  static cmdinfo_t freesp_cmd;
>  static cmdinfo_t resvsp_cmd;
> @@ -41,6 +45,7 @@ static cmdinfo_t fcollapse_cmd;
>  static cmdinfo_t finsert_cmd;
>  static cmdinfo_t fzero_cmd;
>  static cmdinfo_t funshare_cmd;
> +static cmdinfo_t fwzero_cmd;
>  
>  static int
>  offset_length(
> @@ -377,6 +382,27 @@ funshare_f(
>  	return 0;
>  }
>  
> +static int
> +fwzero_f(
> +	int		argc,
> +	char		**argv)
> +{
> +	xfs_flock64_t	segment;
> +	int		mode = FALLOC_FL_WRITE_ZEROES;

Shouldn't this take a -k to add FALLOC_FL_KEEP_SIZE like fzero?

(The code otherwise looks fine to me)

--D

> +
> +	if (!offset_length(argv[1], argv[2], &segment)) {
> +		exitcode = 1;
> +		return 0;
> +	}
> +
> +	if (fallocate(file->fd, mode, segment.l_start, segment.l_len)) {
> +		perror("fallocate");
> +		exitcode = 1;
> +		return 0;
> +	}
> +	return 0;
> +}
> +
>  void
>  prealloc_init(void)
>  {
> @@ -489,4 +515,14 @@ prealloc_init(void)
>  	funshare_cmd.oneline =
>  	_("unshares shared blocks within the range");
>  	add_command(&funshare_cmd);
> +
> +	fwzero_cmd.name = "fwzero";
> +	fwzero_cmd.cfunc = fwzero_f;
> +	fwzero_cmd.argmin = 2;
> +	fwzero_cmd.argmax = 2;
> +	fwzero_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK;
> +	fwzero_cmd.args = _("off len");
> +	fwzero_cmd.oneline =
> +	_("zeroes space and eliminates holes by allocating and submitting write zeroes");
> +	add_command(&fwzero_cmd);
>  }
> diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
> index b0dcfdb7..0a673322 100644
> --- a/man/man8/xfs_io.8
> +++ b/man/man8/xfs_io.8
> @@ -550,6 +550,12 @@ With the
>  .B -k
>  option, use the FALLOC_FL_KEEP_SIZE flag as well.
>  .TP
> +.BI fwzero " offset length"
> +Call fallocate with FALLOC_FL_WRITE_ZEROES flag as described in the
> +.BR fallocate (2)
> +manual page to allocate and zero blocks within the range by submitting write
> +zeroes.
> +.TP
>  .BI zero " offset length"
>  Call xfsctl with
>  .B XFS_IOC_ZERO_RANGE
> -- 
> 2.39.2
> 
>