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Subject[PATCH 08/28] ext4: Record the checksum algorithm in use in the superblock
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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>
---
fs/ext4/ext4.h | 5 ++++-
fs/ext4/super.c | 18 ++++++++++++++++++
2 files changed, 22 insertions(+), 1 deletions(-)


diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 8ee8646..a74e125 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -957,6 +957,9 @@ extern void ext4_set_bits(void *bm, int cur, int len);
#define EXT4_ERRORS_PANIC 3 /* Panic */
#define EXT4_ERRORS_DEFAULT EXT4_ERRORS_CONTINUE

+/* Metadata checksum algorithm codes */
+#define EXT4_CRC32C_CHKSUM 1
+
/*
* Structure of the super block
*/
@@ -1043,7 +1046,7 @@ struct ext4_super_block {
__le64 s_mmp_block; /* Block for multi-mount protection */
__le32 s_raid_stripe_width; /* blocks on all data disks (N*stride)*/
__u8 s_log_groups_per_flex; /* FLEX_BG group size */
- __u8 s_reserved_char_pad;
+ __u8 s_checksum_type; /* metadata checksum algorithm used */
__le16 s_reserved_pad;
__le64 s_kbytes_written; /* nr of lifetime kilobytes written */
__le32 s_snapshot_inum; /* Inode number of active snapshot */
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 44d0c8d..ac33e45 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -110,6 +110,16 @@ 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;
@@ -3153,6 +3163,14 @@ 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);


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