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

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

On Fri, Aug 15, 2025 at 05:59:01PM +0800, Zhang Yi wrote:
> On 2025/8/15 0:54, Darrick J. Wong wrote:
> > On Wed, Aug 13, 2025 at 10:42:50AM +0800, Zhang Yi wrote:
> >> From: Zhang Yi <yi.zhang@huawei.com>
> >>
> >> 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@huawei.com>
> >> ---
> >> 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?
> > 
> 
> Since allocating blocks with written extents beyond the inode size
> is not permitted, the FALLOC_FL_WRITE_ZEROES flag cannot be used
> together with the FALLOC_FL_KEEP_SIZE.

Heh, apparently I didn't read the manpage well enough.

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D


> Thanks,
> Yi.
> 
> > (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
> >>
> >>
> 
>