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

[Zhang Yi <yi.zhang@huaweicloud.com>]

On 8/15/2025 10:29 PM, Darrick J. Wong wrote:
> 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. :)
> 

OK. perhaps "written as zeros." ? Sounds OK?

Thanks,
Yi.