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Message-ID: <20250820175037.GN7981@frogsfrogsfrogs>
Date: Wed, 20 Aug 2025 10:50:37 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
dm-devel@...ts.linux.dev, linux-nvme@...ts.infradead.org,
linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
hch@....de, tytso@....edu, bmarzins@...hat.com,
chaitanyak@...dia.com, shinichiro.kawasaki@....com,
brauner@...nel.org, martin.petersen@...cle.com, yi.zhang@...wei.com,
chengzhihao1@...wei.com, yukuai3@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH util-linux v3] fallocate: add FALLOC_FL_WRITE_ZEROES
support
On Wed, Aug 20, 2025 at 04:56:32PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.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@...wei.com>
> ---
> v2->v3:
> - Say less about what the filesystem actually implements as Darrick
> suggested and clarify the reason why "--keep-size" cannot be used
> together in the man page.
> - Modify the verbose output message.
> 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..a06cf7a50 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
>
> == SYNOPSIS
>
> -*fallocate* [*-c*|*-p*|*-z*] [*-o* _offset_] *-l* _length_ [*-n*] _filename_
> +*fallocate* [*-c*|*-p*|*-z*|*-w*] [*-o* _offset_] *-l* _length_ [*-n*] _filename_
>
> *fallocate* *-d* [*-o* _offset_] [*-l* _length_] _filename_
>
> @@ -28,7 +28,7 @@ The exit status returned by *fallocate* is 0 on success and 1 on failure.
>
> The _length_ and _offset_ arguments may be followed by the multiplicative suffixes KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB, and YiB (the "iB" is optional, e.g., "K" has the same meaning as "KiB") or the suffixes KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB, and YB.
>
> -The options *--collapse-range*, *--dig-holes*, *--punch-hole*, *--zero-range* and *--posix* are mutually exclusive.
> +The options *--collapse-range*, *--dig-holes*, *--punch-hole*, *--zero-range*, *--write-zeroes* and *--posix* are mutually exclusive.
>
> *-c*, *--collapse-range*::
> Removes a byte range from a file, without leaving a hole. The byte range to be collapsed starts at _offset_ and continues for _length_ bytes. At the completion of the operation, the contents of the file starting at the location __offset__+_length_ will be appended at the location _offset_, and the file will be _length_ bytes smaller. The option *--keep-size* may not be specified for the collapse-range operation.
> @@ -76,6 +76,13 @@ Option *--keep-size* can be specified to prevent file length modification.
> +
> Available since Linux 3.14 for ext4 (only for extent-based files) and XFS.
>
> +*-w*, *--write-zeroes*::
> +Zeroes space in the byte range starting at _offset_ and continuing for _length_ bytes. Within the specified range, written 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 and subsequent writes to that range do not require further changes to the file mapping metadata.
> ++
> +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.
> ++
> +Options *--keep-size* can not be specified for the write-zeroes operation because allocating written blocks beyond the inode size is not permitted.
Nit: s/can not/cannot/
With that fixed, this looks fine to me, so
Reviewed-by: "Darrick J. Wong" <djwong@...nel.org>
--D
> +
> include::man-common/help-version.adoc[]
>
> == AUTHORS
> diff --git a/sys-utils/fallocate.c b/sys-utils/fallocate.c
> index 13bf52915..afd615537 100644
> --- a/sys-utils/fallocate.c
> +++ b/sys-utils/fallocate.c
> @@ -40,7 +40,7 @@
> #if defined(HAVE_LINUX_FALLOC_H) && \
> (!defined(FALLOC_FL_KEEP_SIZE) || !defined(FALLOC_FL_PUNCH_HOLE) || \
> !defined(FALLOC_FL_COLLAPSE_RANGE) || !defined(FALLOC_FL_ZERO_RANGE) || \
> - !defined(FALLOC_FL_INSERT_RANGE))
> + !defined(FALLOC_FL_INSERT_RANGE) || !defined(FALLOC_FL_WRITE_ZEROES))
> # include <linux/falloc.h> /* non-libc fallback for FALLOC_FL_* flags */
> #endif
>
> @@ -65,6 +65,10 @@
> # define FALLOC_FL_INSERT_RANGE 0x20
> #endif
>
> +#ifndef FALLOC_FL_WRITE_ZEROES
> +# define FALLOC_FL_WRITE_ZEROES 0x80
> +#endif
> +
> #include "nls.h"
> #include "strutils.h"
> #include "c.h"
> @@ -94,6 +98,7 @@ static void __attribute__((__noreturn__)) usage(void)
> fputs(_(" -o, --offset <num> offset for range operations, in bytes\n"), out);
> fputs(_(" -p, --punch-hole replace a range with a hole (implies -n)\n"), out);
> fputs(_(" -z, --zero-range zero and ensure allocation of a range\n"), out);
> + fputs(_(" -w, --write-zeroes write zeroes and ensure allocation of a range\n"), out);
> #ifdef HAVE_POSIX_FALLOCATE
> fputs(_(" -x, --posix use posix_fallocate(3) instead of fallocate(2)\n"), out);
> #endif
> @@ -304,6 +309,7 @@ int main(int argc, char **argv)
> { "dig-holes", no_argument, NULL, 'd' },
> { "insert-range", no_argument, NULL, 'i' },
> { "zero-range", no_argument, NULL, 'z' },
> + { "write-zeroes", no_argument, NULL, 'w' },
> { "offset", required_argument, NULL, 'o' },
> { "length", required_argument, NULL, 'l' },
> { "posix", no_argument, NULL, 'x' },
> @@ -312,8 +318,8 @@ int main(int argc, char **argv)
> };
>
> static const ul_excl_t excl[] = { /* rows and cols in ASCII order */
> - { 'c', 'd', 'i', 'p', 'x', 'z'},
> - { 'c', 'i', 'n', 'x' },
> + { 'c', 'd', 'i', 'p', 'w', 'x', 'z'},
> + { 'c', 'i', 'n', 'w', 'x' },
> { 0 }
> };
> int excl_st[ARRAY_SIZE(excl)] = UL_EXCL_STATUS_INIT;
> @@ -323,7 +329,7 @@ int main(int argc, char **argv)
> textdomain(PACKAGE);
> close_stdout_atexit();
>
> - while ((c = getopt_long(argc, argv, "hvVncpdizxl:o:", longopts, NULL))
> + while ((c = getopt_long(argc, argv, "hvVncpdizwxl:o:", longopts, NULL))
> != -1) {
>
> err_exclusive_options(c, longopts, excl, excl_st);
> @@ -353,6 +359,9 @@ int main(int argc, char **argv)
> case 'z':
> mode |= FALLOC_FL_ZERO_RANGE;
> break;
> + case 'w':
> + mode |= FALLOC_FL_WRITE_ZEROES;
> + break;
> case 'x':
> #ifdef HAVE_POSIX_FALLOCATE
> posix = 1;
> @@ -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) written as zeroes.\n"),
> + filename, str, length);
> else
> fprintf(stdout, _("%s: %s (%ju bytes) allocated.\n"),
> filename, str, length);
> --
> 2.39.2
>
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