ext4: store checksum seed in superblock
Allow the filesystem to store the metadata checksum seed in the
superblock and add an incompat feature to say that we're using it.
This enables tune2fs to change the UUID on a mounted metadata_csum
FS without having to (racy!) rewrite all disk metadata.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7ef3fa5..43c0cc8 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3196,7 +3196,9 @@
}
/* Precompute checksum seed for all metadata */
- if (ext4_has_metadata_csum(sb))
+ if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_CSUM_SEED))
+ sbi->s_csum_seed = le32_to_cpu(es->s_checksum_seed);
+ else if (ext4_has_metadata_csum(sb))
sbi->s_csum_seed = ext4_chksum(sbi, ~0, es->s_uuid,
sizeof(es->s_uuid));