From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Javier Martinez Canillas <javierm@redhat.com>
Date: Fri, 11 Jun 2021 00:01:29 +0200
Subject: [PATCH] fs/ext2: Ignore checksum seed incompat feature

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.

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 e7dd78e6635..731d346f886 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
