Re: [PATCH] fs/ext2: Ignore checksum seed incompat feature support

[Lukas Czerner]

On Fri, Jun 11, 2021 at 09:36:16PM +0200, Javier Martinez Canillas wrote:
> This incompat feature is used to denote that the filesystem stored its
> metadata checksum seed in the superblock. This is used to allow tune2fs
> to change the UUID on a mounted metadata_csum filesystem without having
> to rewrite all the disk metadata.
> 
> But GRUB doesn't use the metadata checksum in anyway, so can just ignore
> this feature if is enabled. This is consistent with GRUB filesystem code
> in general which just does a best effort to access the filesystem's data.
> 
> It may be removed from the ignored list in the future if supports to do
> metadata checksumming verification is added to the read-only FS driver.

Thanks,

you can add

Reviewed-by: Lukas Czerner <lczerner@redhat.com>

-Lukas

> 
> Suggested-by: Eric Sandeen <esandeen@redhat.com>
> Suggested-by: Lukas Czerner <lczerner@redhat.com>
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
> ---
> 
>  grub-core/fs/ext2.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/grub-core/fs/ext2.c b/grub-core/fs/ext2.c
> index 848bf939dba..238b2d76e38 100644
> --- a/grub-core/fs/ext2.c
> +++ b/grub-core/fs/ext2.c
> @@ -103,6 +103,7 @@ GRUB_MOD_LICENSE ("GPLv3+");
>  #define EXT4_FEATURE_INCOMPAT_64BIT          0x0080
>  #define EXT4_FEATURE_INCOMPAT_MMP            0x0100
>  #define EXT4_FEATURE_INCOMPAT_FLEX_BG                0x0200
> +#define EXT4_FEATURE_INCOMPAT_CSUM_SEED              0x2000
>  #define EXT4_FEATURE_INCOMPAT_ENCRYPT          0x10000
>  
>  /* The set of back-incompatible features this driver DOES support. Add (OR)
> @@ -123,9 +124,16 @@ GRUB_MOD_LICENSE ("GPLv3+");
>   * mmp:            Not really back-incompatible - was added as such to
>   *                 avoid multiple read-write mounts. Safe to ignore for this
>   *                 RO driver.
> + * checksum seed:  Not really back-incompatible - was added to allow tools
> + *                 such as tune2fs to change the UUID on a mounted metadata
> + *                 checksummed filesystem. Safe to ignore for now since the
> + *                 driver doesn't support checksum verification. But it must
> + *                 be removed from this list if that support is added later.
> + *
>   */
>  #define EXT2_DRIVER_IGNORED_INCOMPAT ( EXT3_FEATURE_INCOMPAT_RECOVER \
> -                                  | EXT4_FEATURE_INCOMPAT_MMP)
> +                                  | EXT4_FEATURE_INCOMPAT_MMP \
> +                                  | EXT4_FEATURE_INCOMPAT_CSUM_SEED)
>  
>  
>  #define EXT3_JOURNAL_MAGIC_NUMBER    0xc03b3998U
> -- 
> 2.31.1
>