* Re: [PATCH v2] man2/fallocate.2: add doc for FALLOC_FL_WRITE_ZEROES
2026-08-20 9:04 [PATCH v2] man2/fallocate.2: add doc for FALLOC_FL_WRITE_ZEROES Pankaj Raghav
@ 2026-08-20 9:28 ` Alejandro Colomar
2026-08-20 9:31 ` Pankaj Raghav
2026-08-21 3:39 ` Zhang Yi
2026-08-22 12:41 ` Alejandro Colomar
2 siblings, 1 reply; 5+ messages in thread
From: Alejandro Colomar @ 2026-08-20 9:28 UTC (permalink / raw)
To: Pankaj Raghav
Cc: linux-man, pankaj.raghav, hch, Zhang Yi, linux-xfs, gost.dev,
Darrick J . Wong, linux-ext4
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Hi Pankaj,
> Date: 2026-08-20 11:04:00+0200
> From: Pankaj Raghav <p.raghav@samsung.com>
>
> This flag was added to the kernel in v6.17. As of now, only ext4 and
> block device nodes support this flag.
>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
> Changes since v1:
> - Change the phrasing around zeroing and its condition (Zhang Yi)
> - Update ext4 support only for extent-based files (Zhang Yi)
>
> Note:
> This feature was recently added to XFS and it is expected to land in
> v7.13. I will update this man page again once v7.13 is released.
Do you really mean Linux v7.13?
Have a lovely day!
Alex
>
> man/man2/fallocate.2 | 38 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
>
> diff --git a/man/man2/fallocate.2 b/man/man2/fallocate.2
> index ef6586c77..48a8c3468 100644
> --- a/man/man2/fallocate.2
> +++ b/man/man2/fallocate.2
> @@ -244,6 +244,43 @@ SMB3 (since Linux 3.17)
> .IP \[bu]
> Btrfs (since Linux 4.16)
> .\" commit f27451f229966874a8793995b8e6b74326d125df
> +.SS Writing zeroes in file space
> +Specifying the
> +.B FALLOC_FL_WRITE_ZEROES
> +flag (available since Linux 6.17)
> +.\" commit 7bd43cc79cab3850f34da0a31d5b042b701590ef
> +in
> +.I mode
> +physically zeros space in the byte range starting at
> +.I offset
> +and continuing for
> +.I size
> +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 zeros and
> +subsequent writes to that range do not require further
> +changes to the file mapping metadata.
> +.P
> +Zeroing is done within the filesystem.
> +The filesystem may use a hardware-accelerated zeroing command
> +or may submit regular writes.
> +The behavior depends on the filesystem design and the
> +available hardware.
> +.P
> +No other flags may be specified in
> +.I mode
> +in conjunction with
> +.BR FALLOC_FL_WRITE_ZEROES .
> +.P
> +Not all filesystems support
> +.BR FALLOC_FL_WRITE_ZEROES ;
> +if a filesystem doesn't support the operation, an error is returned.
> +The operation is supported only in ext4 (only for extent-based files)
> +since Linux 6.17.
> +.\" commit f4265b8d32c49ff95711e6fef7d05245a2905b30
> .SS Increasing file space
> Specifying the
> .B FALLOC_FL_INSERT_RANGE
> @@ -385,6 +422,7 @@ or
> is
> .BR FALLOC_FL_COLLAPSE_RANGE ,
> .BR FALLOC_FL_ZERO_RANGE ,
> +.BR FALLOC_FL_WRITE_ZEROES ,
> or
> .BR FALLOC_FL_INSERT_RANGE ,
> but the file referred to by
>
> base-commit: d926b42e0ea0406d5c2556e18205eced92d053f1
> --
> 2.51.2
>
--
<https://www.alejandro-colomar.es>
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] man2/fallocate.2: add doc for FALLOC_FL_WRITE_ZEROES
2026-08-20 9:28 ` Alejandro Colomar
@ 2026-08-20 9:31 ` Pankaj Raghav
0 siblings, 0 replies; 5+ messages in thread
From: Pankaj Raghav @ 2026-08-20 9:31 UTC (permalink / raw)
To: Alejandro Colomar, Pankaj Raghav
Cc: linux-man, hch, Zhang Yi, linux-xfs, gost.dev, Darrick J . Wong,
linux-ext4
On 8/20/26 11:28, Alejandro Colomar wrote:
> Hi Pankaj,
>
>> Date: 2026-08-20 11:04:00+0200
>> From: Pankaj Raghav <p.raghav@samsung.com>
>>
>> This flag was added to the kernel in v6.17. As of now, only ext4 and
>> block device nodes support this flag.
>>
>> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
>> ---
>> Changes since v1:
>> - Change the phrasing around zeroing and its condition (Zhang Yi)
>> - Update ext4 support only for extent-based files (Zhang Yi)
>>
>> Note:
>> This feature was recently added to XFS and it is expected to land in
>> v7.13. I will update this man page again once v7.13 is released.
>
> Do you really mean Linux v7.13?
>
>
Oops. I mean v7.3 :)
--
Pankaj
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] man2/fallocate.2: add doc for FALLOC_FL_WRITE_ZEROES
2026-08-20 9:04 [PATCH v2] man2/fallocate.2: add doc for FALLOC_FL_WRITE_ZEROES Pankaj Raghav
2026-08-20 9:28 ` Alejandro Colomar
@ 2026-08-21 3:39 ` Zhang Yi
2026-08-22 12:41 ` Alejandro Colomar
2 siblings, 0 replies; 5+ messages in thread
From: Zhang Yi @ 2026-08-21 3:39 UTC (permalink / raw)
To: Pankaj Raghav, linux-man, Alejandro Colomar
Cc: pankaj.raghav, hch, linux-xfs, gost.dev, Darrick J . Wong,
linux-ext4
On 8/20/2026 5:04 PM, Pankaj Raghav wrote:
> This flag was added to the kernel in v6.17. As of now, only ext4 and
> block device nodes support this flag.
>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Looks good to me. Thanks!
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
> ---
> Changes since v1:
> - Change the phrasing around zeroing and its condition (Zhang Yi)
> - Update ext4 support only for extent-based files (Zhang Yi)
>
> Note:
> This feature was recently added to XFS and it is expected to land in
> v7.13. I will update this man page again once v7.13 is released.
>
> man/man2/fallocate.2 | 38 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
>
> diff --git a/man/man2/fallocate.2 b/man/man2/fallocate.2
> index ef6586c77..48a8c3468 100644
> --- a/man/man2/fallocate.2
> +++ b/man/man2/fallocate.2
> @@ -244,6 +244,43 @@ SMB3 (since Linux 3.17)
> .IP \[bu]
> Btrfs (since Linux 4.16)
> .\" commit f27451f229966874a8793995b8e6b74326d125df
> +.SS Writing zeroes in file space
> +Specifying the
> +.B FALLOC_FL_WRITE_ZEROES
> +flag (available since Linux 6.17)
> +.\" commit 7bd43cc79cab3850f34da0a31d5b042b701590ef
> +in
> +.I mode
> +physically zeros space in the byte range starting at
> +.I offset
> +and continuing for
> +.I size
> +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 zeros and
> +subsequent writes to that range do not require further
> +changes to the file mapping metadata.
> +.P
> +Zeroing is done within the filesystem.
> +The filesystem may use a hardware-accelerated zeroing command
> +or may submit regular writes.
> +The behavior depends on the filesystem design and the
> +available hardware.
> +.P
> +No other flags may be specified in
> +.I mode
> +in conjunction with
> +.BR FALLOC_FL_WRITE_ZEROES .
> +.P
> +Not all filesystems support
> +.BR FALLOC_FL_WRITE_ZEROES ;
> +if a filesystem doesn't support the operation, an error is returned.
> +The operation is supported only in ext4 (only for extent-based files)
> +since Linux 6.17.
> +.\" commit f4265b8d32c49ff95711e6fef7d05245a2905b30
> .SS Increasing file space
> Specifying the
> .B FALLOC_FL_INSERT_RANGE
> @@ -385,6 +422,7 @@ or
> is
> .BR FALLOC_FL_COLLAPSE_RANGE ,
> .BR FALLOC_FL_ZERO_RANGE ,
> +.BR FALLOC_FL_WRITE_ZEROES ,
> or
> .BR FALLOC_FL_INSERT_RANGE ,
> but the file referred to by
>
> base-commit: d926b42e0ea0406d5c2556e18205eced92d053f1
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] man2/fallocate.2: add doc for FALLOC_FL_WRITE_ZEROES
2026-08-20 9:04 [PATCH v2] man2/fallocate.2: add doc for FALLOC_FL_WRITE_ZEROES Pankaj Raghav
2026-08-20 9:28 ` Alejandro Colomar
2026-08-21 3:39 ` Zhang Yi
@ 2026-08-22 12:41 ` Alejandro Colomar
2 siblings, 0 replies; 5+ messages in thread
From: Alejandro Colomar @ 2026-08-22 12:41 UTC (permalink / raw)
To: Pankaj Raghav
Cc: linux-man, pankaj.raghav, hch, Zhang Yi, linux-xfs, gost.dev,
Darrick J . Wong, linux-ext4
[-- Attachment #1: Type: text/plain, Size: 3537 bytes --]
Hi Pankaj, Christoph,
> Date: 2026-08-20 11:04:00+0200
> From: Pankaj Raghav <p.raghav@samsung.com>
> Subject: Re: [PATCH v2] man2/fallocate.2: add doc for FALLOC_FL_WRITE_ZEROES
We use the full path in the prefix. That is, 'man/man2/...: ...'.
Also, we use regular sentence conventions for the first letter after
the ':', so s/add/Add/.
> This flag was added to the kernel in v6.17. As of now, only ext4 and
Please use two spaces after period.
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING.d/patches/description#n44>
> block device nodes support this flag.
>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Please include the CC list here too.
> ---
> Changes since v1:
> - Change the phrasing around zeroing and its condition (Zhang Yi)
> - Update ext4 support only for extent-based files (Zhang Yi)
>
> Note:
> This feature was recently added to XFS and it is expected to land in
> v7.13. I will update this man page again once v7.13 is released.
>
> man/man2/fallocate.2 | 38 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
>
> diff --git a/man/man2/fallocate.2 b/man/man2/fallocate.2
> index ef6586c77..48a8c3468 100644
> --- a/man/man2/fallocate.2
> +++ b/man/man2/fallocate.2
> @@ -244,6 +244,43 @@ SMB3 (since Linux 3.17)
> .IP \[bu]
> Btrfs (since Linux 4.16)
> .\" commit f27451f229966874a8793995b8e6b74326d125df
> +.SS Writing zeroes in file space
> +Specifying the
> +.B FALLOC_FL_WRITE_ZEROES
> +flag (available since Linux 6.17)
> +.\" commit 7bd43cc79cab3850f34da0a31d5b042b701590ef
> +in
> +.I mode
> +physically zeros space in the byte range starting at
> +.I offset
> +and continuing for
> +.I size
> +bytes.
> +Within the specified range,
> +blocks are preallocated for the regions that span the holes
What does it mean that "blocks are preallocated"? That they must be
allocated prior to this call? I suspect not. Otherwise, we'd be saying
'must be' instead of 'are'.
I suspect it means that this call allocates blocks for those regions,
but then I'm not sure we want 'pre' there.
> +in the file.
> +After a successful call,
> +subsequent reads from this range will return zeros and
> +subsequent writes to that range do not require further
> +changes to the file mapping metadata.
> +.P
> +Zeroing is done within the filesystem.
> +The filesystem may use a hardware-accelerated zeroing command
> +or may submit regular writes.
> +The behavior depends on the filesystem design and the
> +available hardware.
> +.P
> +No other flags may be specified in
> +.I mode
> +in conjunction with
> +.BR FALLOC_FL_WRITE_ZEROES .
> +.P
> +Not all filesystems support
> +.BR FALLOC_FL_WRITE_ZEROES ;
> +if a filesystem doesn't support the operation, an error is returned.
> +The operation is supported only in ext4 (only for extent-based files)
> +since Linux 6.17.
Christoph, is this correct? I remember you said something about block
device nodes in v1.
Have a lovely day!
Alex
> +.\" commit f4265b8d32c49ff95711e6fef7d05245a2905b30
> .SS Increasing file space
> Specifying the
> .B FALLOC_FL_INSERT_RANGE
> @@ -385,6 +422,7 @@ or
> is
> .BR FALLOC_FL_COLLAPSE_RANGE ,
> .BR FALLOC_FL_ZERO_RANGE ,
> +.BR FALLOC_FL_WRITE_ZEROES ,
> or
> .BR FALLOC_FL_INSERT_RANGE ,
> but the file referred to by
>
> base-commit: d926b42e0ea0406d5c2556e18205eced92d053f1
> --
> 2.51.2
>
--
<https://www.alejandro-colomar.es>
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^ permalink raw reply [flat|nested] 5+ messages in thread