Messages in this thread Patch in this message |  | | From | Arnd Bergmann <> | | Subject | [PATCH] [v2] ext4: fix ext4_tune_sb_params padding | | Date | Fri, 5 Dec 2025 12:19:00 +0100 |
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From: Arnd Bergmann <arnd@arndb.de>
The padding at the end of struct ext4_tune_sb_params is architecture specific and in particular is different between x86-32 and x86-64, since the __u64 member only enforces struct alignment on the latter.
This shows up as a new warning when test-building the headers with -Wpadded:
include/linux/ext4.h:144:1: error: padding struct size to alignment boundary with 4 bytes [-Werror=padded]
All members inside the structure are naturally aligned, so the only difference here is the amount of padding at the end.
Add explicit padding to mount_opts[] to keep the struct members compatible with the original version and also keep the pad[64] member 8-byte aligned for future extensions. This gives a consistent sizeof(struct ext4_tune_sb_params) of 232 on all architectures and avoids adding compat ioctl handling for EXT4_IOC_GET_TUNE_SB_PARAM/EXT4_IOC_SET_TUNE_SB_PARAM.
This is an ABI break on x86-32 but hopefully this can go into 6.18.y early enough as a fixup so no actual users will be affected.
Fixes: 04a91570ac67 ("ext4: implemet new ioctls to set and get superblock parameters") Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- v2: extend mount_opts[] instead of pad[], as suggested by Andreas Dilger --- include/uapi/linux/ext4.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h index 6829d6f1497d..1c7cdcdb7dca 100644 --- a/include/uapi/linux/ext4.h +++ b/include/uapi/linux/ext4.h @@ -139,7 +139,7 @@ struct ext4_tune_sb_params { __u32 clear_feature_compat_mask; __u32 clear_feature_incompat_mask; __u32 clear_feature_ro_compat_mask; - __u8 mount_opts[64]; + __u8 mount_opts[68]; __u8 pad[64]; }; -- 2.39.5
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