Re: [PATCH util-linux v2] fallocate: add FALLOC_FL_WRITE_ZEROES support

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

On Fri, Aug 15, 2025 at 05:29:19PM +0800, Zhang Yi wrote:
> Thank you for your review comments!
> 
> On 2025/8/15 0:52, Darrick J. Wong wrote:
> > On Wed, Aug 13, 2025 at 10:40:15AM +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 to the fallocate
> >> utility by introducing a new option -w|--write-zeroes.
> >>
> >> 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.
> >>
> >>  sys-utils/fallocate.1.adoc | 11 +++++++++--
> >>  sys-utils/fallocate.c      | 20 ++++++++++++++++----
> >>  2 files changed, 25 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/sys-utils/fallocate.1.adoc b/sys-utils/fallocate.1.adoc
> >> index 44ee0ef4c..0ec9ff9a9 100644
> >> --- a/sys-utils/fallocate.1.adoc
> >> +++ b/sys-utils/fallocate.1.adoc
> >> @@ -12,7 +12,7 @@ fallocate - preallocate or deallocate space to a file
> > 
> > <snip all the long lines>
> > 
> >> +*-w*, *--write-zeroes*::
> >> +Zeroes space in the byte range starting at _offset_ and continuing
> >> for _length_ bytes. Within the specified range, blocks are
> >> preallocated for the regions that span the holes in the file. After a
> >> successful call, subsequent reads from this range will return zeroes,
> >> subsequent writes to that range do not require further changes to the
> >> file mapping metadata.
> > 
> > "...will return zeroes and subsequent writes to that range..." ?
> > 
> 
> Yeah.
> 
> >> ++
> >> +Zeroing is done within the filesystem by preferably submitting write
> > 
> > I think we should say less about what the filesystem actually does to
> > preserve some flexibility:
> > 
> > "Zeroing is done within the filesystem. The filesystem may use a
> > hardware accelerated zeroing command, or it may submit regular writes.
> > The behavior depends on the filesystem design and available hardware."
> > 
> 
> Sure.
> 
> >> zeores commands, the alternative way is submitting actual zeroed data,
> >> the specified range will be converted into written extents. The write
> >> zeroes command is typically faster than write actual data if the
> >> device supports unmap write zeroes, the specified range will not be
> >> physically zeroed out on the device.
> >> ++
> >> +Options *--keep-size* can not be specified for the write-zeroes
> >> operation.
> >> +
> >>  include::man-common/help-version.adoc[]
> >>  
> >>  == AUTHORS
> [..]
> >> @@ -429,6 +438,9 @@ int main(int argc, char **argv)
> >>  			else if (mode & FALLOC_FL_ZERO_RANGE)
> >>  				fprintf(stdout, _("%s: %s (%ju bytes) zeroed.\n"),
> >>  								filename, str, length);
> >> +			else if (mode & FALLOC_FL_WRITE_ZEROES)
> >> +				fprintf(stdout, _("%s: %s (%ju bytes) write zeroed.\n"),
> > 
> > "write zeroed" is a little strange, but I don't have a better
> > suggestion. :)
> > 
> 
> Hmm... What about simply using "zeroed", the same to FALLOC_FL_ZERO_RANGE?
> Users should be aware of the parameters they have passed to fallocate(),
> so they should not use this print for further differentiation.

No thanks, different inputs should produce different outputs. :)

--D

> Thanks,
> Yi.
>