linux-ext4 - Re: [PATCH v2 1/4] mke2fs: document the hash

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Message-Id: <F29BC06C-B943-4D2A-ACDB-2DE9FC015280@dilger.ca>
Date: Sat, 20 Sep 2025 12:52:38 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: Ralph Siemsen <ralph.siemsen@...aro.org>
Cc: linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2 1/4] mke2fs: document the hash_seed option

On Sep 10, 2025, at 7:51 AM, Ralph Siemsen <ralph.siemsen@...aro.org> wrote:
> 
> For reproducible builds, it is necessary to control the random seed used
> for hashing. Document the extended option for this feature.
> 
> Fixes: e1f71006 ("AOSP: mke2fs, libext2fs: make filesystem image reproducible")
> Signed-off-by: Ralph Siemsen <ralph.siemsen@...aro.org>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> ---
> misc/mke2fs.8.in | 4 ++++
> misc/mke2fs.c    | 1 +
> 2 files changed, 5 insertions(+)
> 
> diff --git a/misc/mke2fs.8.in b/misc/mke2fs.8.in
> index 13ddef47..14bae326 100644
> --- a/misc/mke2fs.8.in
> +++ b/misc/mke2fs.8.in
> @@ -320,6 +320,10 @@ In the default configuration, the
> .I strict
> flag is disabled.
> .TP
> +.BI hash_seed= UUID
> +Use the specified UUID as the seed for hashing, rather than generating a
> +random seed each time. Intended for use with reproducible builds.
> +.TP
> .B lazy_itable_init\fR[\fB= \fI<0 to disable, 1 to enable>\fR]
> If enabled and the uninit_bg feature is enabled, the inode table will
> not be fully initialized by
> diff --git a/misc/mke2fs.c b/misc/mke2fs.c
> index 7f81a513..3a8ff5b1 100644
> --- a/misc/mke2fs.c
> +++ b/misc/mke2fs.c
> @@ -1180,6 +1180,7 @@ static void parse_extended_opts(struct ext2_super_block *param,
> 			"\trevision=<revision>\n"
> 			"\tencoding=<encoding>\n"
> 			"\tencoding_flags=<flags>\n"
> +			"\thash_seed=<UUID for hash seed>\n"
> 			"\tquotatype=<quota type(s) to be enabled>\n"
> 			"\tassume_storage_prezeroed=<0 to disable, 1 to enable>\n\n"),
> 			badopt ? badopt : "");
> 
> --
> 2.45.2.121.gc2b3f2b3cd
> 
> 


Cheers, Andreas






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