ext4: change on-disk layout to support extended metadata checksumming

Define flags and change structure definitions to allow checksumming of
ext4 metadata.

Signed-off-by: Darrick J. Wong <[e-mail]>
Signed-off-by: "Theodore Ts'o" <[e-mail]>

fs/ext4/ext4.h

···
 	__le16	bg_free_inodes_count_lo;/* Free inodes count */
 	__le16	bg_used_dirs_count_lo;	/* Directories count */
 	__le16	bg_flags;		/* EXT4_BG_flags (INODE_UNINIT, etc) */
-	__u32	bg_reserved[2];		/* Likely block/inode bitmap checksum */
+	__le32  bg_exclude_bitmap_lo;   /* Exclude bitmap for snapshots */
+	__le16  bg_block_bitmap_csum_lo;/* crc32c(s_uuid+grp_num+bbitmap) LE */
+	__le16  bg_inode_bitmap_csum_lo;/* crc32c(s_uuid+grp_num+ibitmap) LE */
 	__le16  bg_itable_unused_lo;	/* Unused inodes count */
 	__le16  bg_checksum;		/* crc16(sb_uuid+group+desc) */
 	__le32	bg_block_bitmap_hi;	/* Blocks bitmap block MSB */
···
 	__le16	bg_free_inodes_count_hi;/* Free inodes count MSB */
 	__le16	bg_used_dirs_count_hi;	/* Directories count MSB */
 	__le16  bg_itable_unused_hi;    /* Unused inodes count MSB */
-	__u32	bg_reserved2[3];
+	__le32  bg_exclude_bitmap_hi;   /* Exclude bitmap block MSB */
+	__le16  bg_block_bitmap_csum_hi;/* crc32c(s_uuid+grp_num+bbitmap) BE */
+	__le16  bg_inode_bitmap_csum_hi;/* crc32c(s_uuid+grp_num+ibitmap) BE */
+	__u32   bg_reserved;
 };
 
 /*
···
 			__le16	l_i_file_acl_high;
 			__le16	l_i_uid_high;	/* these 2 fields */
 			__le16	l_i_gid_high;	/* were reserved2[0] */
-			__u32	l_i_reserved2;
+			__le16	l_i_checksum_lo;/* crc32c(uuid+inum+inode) LE */
+			__le16	l_i_reserved;
 		} linux2;
 		struct {
 			__le16	h_i_reserved1;	/* Obsoleted fragment number/size which are removed in ext4 */
···
 		} masix2;
 	} osd2;				/* OS dependent 2 */
 	__le16	i_extra_isize;
-	__le16	i_pad1;
+	__le16	i_checksum_hi;	/* crc32c(uuid+inum+inode) BE */
 	__le32  i_ctime_extra;  /* extra Change time      (nsec << 2 | epoch) */
 	__le32  i_mtime_extra;  /* extra Modification time(nsec << 2 | epoch) */
 	__le32  i_atime_extra;  /* extra Access time      (nsec << 2 | epoch) */
···
 #define i_gid_low	i_gid
 #define i_uid_high	osd2.linux2.l_i_uid_high
 #define i_gid_high	osd2.linux2.l_i_gid_high
-#define i_reserved2	osd2.linux2.l_i_reserved2
+#define i_checksum_lo	osd2.linux2.l_i_checksum_lo
 
 #elif defined(__GNU__)
 
···
 #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
  */
···
 	__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 */
···
 	__le32	s_usr_quota_inum;	/* inode for tracking user quota */
 	__le32	s_grp_quota_inum;	/* inode for tracking group quota */
 	__le32	s_overhead_clusters;	/* overhead blocks/clusters in fs */
-	__le32  s_reserved[109];        /* Padding to the end of the block */
+	__le32	s_reserved[108];	/* Padding to the end of the block */
+	__le32	s_checksum;		/* crc32c(superblock) */
 };
 
 #define EXT4_S_ERR_LEN (EXT4_S_ERR_END - EXT4_S_ERR_START)
···
 #define EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE	0x0040
 #define EXT4_FEATURE_RO_COMPAT_QUOTA		0x0100
 #define EXT4_FEATURE_RO_COMPAT_BIGALLOC		0x0200
+/*
+ * METADATA_CSUM also enables group descriptor checksums (GDT_CSUM).  When
+ * METADATA_CSUM is set, group descriptor checksums use the same algorithm as
+ * all other data structures' checksums.  However, the METADATA_CSUM and
+ * GDT_CSUM bits are mutually exclusive.
+ */
 #define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM	0x0400
 
 #define EXT4_FEATURE_INCOMPAT_COMPRESSION	0x0001
···
 };
 
 /*
+ * This is a bogus directory entry at the end of each leaf block that
+ * records checksums.
+ */
+struct ext4_dir_entry_tail {
+	__le32	det_reserved_zero1;	/* Pretend to be unused */
+	__le16	det_rec_len;		/* 12 */
+	__u8	det_reserved_zero2;	/* Zero name length */
+	__u8	det_reserved_ft;	/* 0xDE, fake file type */
+	__le32	det_checksum;		/* crc32c(uuid+inum+dirblock) */
+};
+
+/*
  * Ext4 directory file types.  Only the low 3 bits are used.  The
  * other bits are reserved for now.
  */
···
 #define EXT4_FT_SYMLINK		7
 
 #define EXT4_FT_MAX		8
+
+#define EXT4_FT_DIR_CSUM	0xDE
 
 /*
  * EXT4_DIR_PAD defines the directory entries boundaries
···
 	__le16	mmp_check_interval;
 
 	__le16	mmp_pad1;
-	__le32	mmp_pad2[227];
+	__le32	mmp_pad2[226];
+	__le32	mmp_checksum;		/* crc32c(uuid+mmp_block) */
 };
 
 /* arguments passed to the mmp thread */

fs/ext4/ext4_extents.h

···
  * ext4_inode has i_block array (60 bytes total).
  * The first 12 bytes store ext4_extent_header;
  * the remainder stores an array of ext4_extent.
+ * For non-inode extent blocks, ext4_extent_tail
+ * follows the array.
  */
+
+/*
+ * This is the extent tail on-disk structure.
+ * All other extent structures are 12 bytes long.  It turns out that
+ * block_size % 12 >= 4 for at least all powers of 2 greater than 512, which
+ * covers all valid ext4 block sizes.  Therefore, this tail structure can be
+ * crammed into the end of the block without having to rebalance the tree.
+ */
+struct ext4_extent_tail {
+	__le32	et_checksum;	/* crc32c(uuid+inum+extent_block) */
+};
 
 /*
  * This is the extent on-disk structure.

fs/ext4/namei.c

···
 	u16 size;
 };
 
+/*
+ * This goes at the end of each htree block.
+ */
+struct dx_tail {
+	u32 dt_reserved;
+	__le32 dt_checksum;	/* crc32c(uuid+inum+dirblock) */
+};
+
 static inline ext4_lblk_t dx_get_block(struct dx_entry *entry);
 static void dx_set_block(struct dx_entry *entry, ext4_lblk_t value);
 static inline unsigned dx_get_hash(struct dx_entry *entry);

fs/ext4/xattr.h

···
 	__le32	h_refcount;	/* reference count */
 	__le32	h_blocks;	/* number of disk blocks used */
 	__le32	h_hash;		/* hash value of all attributes */
-	__u32	h_reserved[4];	/* zero right now */
+	__le32	h_checksum;	/* crc32c(uuid+id+xattrblock) */
+				/* id = inum if refcount=1, blknum otherwise */
+	__u32	h_reserved[3];	/* zero right now */
 };
 
 struct ext4_xattr_ibody_header {