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

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Message-Id: <20250910-mke2fs-small-fixes-v2-1-55c9842494e0@linaro.org>
Date: Wed, 10 Sep 2025 09:51:45 -0400
From: Ralph Siemsen <ralph.siemsen@...aro.org>
To: linux-ext4@...r.kernel.org
Cc: Ralph Siemsen <ralph.siemsen@...aro.org>
Subject: [PATCH v2 1/4] mke2fs: document the hash_seed option

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>
---
 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