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/ext4.h b/fs/ext4/ext4.h
index 320f10ef4a23382e4e3239213641e305050f0f51..cd832b99f68c6e3a8a6e542f4e417510c1aa2593 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1184,7 +1184,8 @@ struct ext4_super_block {
        __u8    s_encrypt_pw_salt[16];  /* Salt used for string2key algorithm */
        __le32  s_lpf_ino;              /* Location of the lost+found inode */
        __le32  s_prj_quota_inum;       /* inode for tracking project quota */
-       __le32  s_reserved[99];         /* Padding to the end of the block */
+       __le32  s_checksum_seed;        /* crc32c(uuid) if csum_seed set */
+       __le32  s_reserved[98];         /* Padding to the end of the block */
        __le32  s_checksum;             /* crc32c(superblock) */
 };
 
@@ -1584,7 +1585,7 @@ static inline int ext4_encrypted_inode(struct inode *inode)
 #define EXT4_FEATURE_INCOMPAT_FLEX_BG          0x0200
 #define EXT4_FEATURE_INCOMPAT_EA_INODE         0x0400 /* EA in inode */
 #define EXT4_FEATURE_INCOMPAT_DIRDATA          0x1000 /* data in dirent */
-#define EXT4_FEATURE_INCOMPAT_BG_USE_META_CSUM 0x2000 /* use crc32c for bg */
+#define EXT4_FEATURE_INCOMPAT_CSUM_SEED                0x2000
 #define EXT4_FEATURE_INCOMPAT_LARGEDIR         0x4000 /* >2GB or 3-lvl htree */
 #define EXT4_FEATURE_INCOMPAT_INLINE_DATA      0x8000 /* data in inode */
 #define EXT4_FEATURE_INCOMPAT_ENCRYPT          0x10000
@@ -1613,7 +1614,8 @@ static inline int ext4_encrypted_inode(struct inode *inode)
                                         EXT4_FEATURE_INCOMPAT_FLEX_BG| \
                                         EXT4_FEATURE_INCOMPAT_MMP | \
                                         EXT4_FEATURE_INCOMPAT_INLINE_DATA | \
-                                        EXT4_FEATURE_INCOMPAT_ENCRYPT)
+                                        EXT4_FEATURE_INCOMPAT_ENCRYPT | \
+                                        EXT4_FEATURE_INCOMPAT_CSUM_SEED)
 #define EXT4_FEATURE_RO_COMPAT_SUPP    (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
                                         EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
                                         EXT4_FEATURE_RO_COMPAT_GDT_CSUM| \

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7ef3fa58d3fe7c6d5e7c0bb04f9181f2a7e4f748..43c0cc802189f89333e353bd7a5bf4257f1d57fc 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3196,7 +3196,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
        }
 
        /* 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));
 

diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index 62bef0f0642172665598de5928fd7fc0cbc14b27..1b57c72f4a009aafc8c3510eac81dd9d8a5f9482 100644 (file)
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -224,12 +224,14 @@ EXT4_ATTR_FEATURE(lazy_itable_init);
 EXT4_ATTR_FEATURE(batched_discard);
 EXT4_ATTR_FEATURE(meta_bg_resize);
 EXT4_ATTR_FEATURE(encryption);
+EXT4_ATTR_FEATURE(metadata_csum_seed);
 
 static struct attribute *ext4_feat_attrs[] = {
        ATTR_LIST(lazy_itable_init),
        ATTR_LIST(batched_discard),
        ATTR_LIST(meta_bg_resize),
        ATTR_LIST(encryption),
+       ATTR_LIST(metadata_csum_seed),
        NULL,
 };