ext4: record the checksum algorithm in use in the superblock

Record the type of checksum algorithm we're using for metadata in the
superblock, in case we ever want/need to change the algorithm.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 18 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e1fb1d5de58e..f489ffb3605d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -112,6 +112,16 @@ static struct file_system_type ext3_fs_type = {
 #define IS_EXT3_SB(sb) (0)
 #endif
 
+static int ext4_verify_csum_type(struct super_block *sb,
+                                 struct ext4_super_block *es)
+{
+        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
+                                        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+                return 1;
+
+        return es->s_checksum_type == EXT4_CRC32C_CHKSUM;
+}
+
 void *ext4_kvmalloc(size_t size, gfp_t flags)
 {
         void *ret;
@@ -3025,6 +3035,14 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                 goto cantfind_ext4;
         sbi->s_kbytes_written = le64_to_cpu(es->s_kbytes_written);
 
+        /* Check for a known checksum algorithm */
+        if (!ext4_verify_csum_type(sb, es)) {
+                ext4_msg(sb, KERN_ERR, "VFS: Found ext4 filesystem with "
+                         "unknown checksum algorithm.");
+                silent = 1;
+                goto cantfind_ext4;
+        }
+
         /* Set defaults before we parse the mount options */
         def_mount_opts = le32_to_cpu(es->s_default_mount_opts);
         set_opt(sb, INIT_INODE_TABLE);