[PATCH v3] man/man2/fallocate.2: Add doc for FALLOC_FL_WRITE_ZEROES
flat view
COLD26d
From: Pankaj Raghav <hidden>
Date: 2026-09-10 11:20:34
Also in:
linux-ext4, linux-xfs
Subsystem:
the rest · Maintainer:
Linus Torvalds
This flag was added to the kernel in v6.17. As of now, only ext4 and block device nodes support this flag. Cc: Zhang Yi <redacted> Cc: Christoph Hellwig <hch@lst.de> Cc: Darrick J. Wong <djwong@kernel.org> Cc: gost.dev@samsung.com Cc: linux-ext4@vger.kernel.org Cc: linux-xfs@vger.kernel.org Signed-off-by: Pankaj Raghav <redacted> --- Changes since v2: - Changed the commit format based on Alejandro's feedback. - I have retained "preallocated" term based on Zhang Yi's feedback[1] Note: This feature was recently added to XFS and it is expected to land in v7.3. I will update this man page again once v7.3 is released. [1] https://lore.kernel.org/linux-man/3f17d214-f69c-47b6-abf6-4437cc5840c0@huaweicloud.com/ (local) 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