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      1 /*
      2  *  linux/include/linux/ext2_fs.h
      3  *
      4  * Copyright (C) 1992, 1993, 1994, 1995
      5  * Remy Card (card (at) masi.ibp.fr)
      6  * Laboratoire MASI - Institut Blaise Pascal
      7  * Universite Pierre et Marie Curie (Paris VI)
      8  *
      9  *  from
     10  *
     11  *  linux/include/linux/minix_fs.h
     12  *
     13  *  Copyright (C) 1991, 1992  Linus Torvalds
     14  */
     15 
     16 #ifndef _LINUX_EXT2_FS_H
     17 #define _LINUX_EXT2_FS_H
     18 
     19 #include <ext2fs/ext2_types.h>		/* Changed from linux/types.h */
     20 
     21 /*
     22  * The second extended filesystem constants/structures
     23  */
     24 
     25 /*
     26  * Define EXT2FS_DEBUG to produce debug messages
     27  */
     28 #undef EXT2FS_DEBUG
     29 
     30 /*
     31  * Define EXT2_PREALLOCATE to preallocate data blocks for expanding files
     32  */
     33 #define EXT2_PREALLOCATE
     34 #define EXT2_DEFAULT_PREALLOC_BLOCKS	8
     35 
     36 /*
     37  * The second extended file system version
     38  */
     39 #define EXT2FS_DATE		"95/08/09"
     40 #define EXT2FS_VERSION		"0.5b"
     41 
     42 /*
     43  * Special inode numbers
     44  */
     45 #define EXT2_BAD_INO		 1	/* Bad blocks inode */
     46 #define EXT2_ROOT_INO		 2	/* Root inode */
     47 #define EXT4_USR_QUOTA_INO	 3	/* User quota inode */
     48 #define EXT4_GRP_QUOTA_INO	 4	/* Group quota inode */
     49 #define EXT2_BOOT_LOADER_INO	 5	/* Boot loader inode */
     50 #define EXT2_UNDEL_DIR_INO	 6	/* Undelete directory inode */
     51 #define EXT2_RESIZE_INO		 7	/* Reserved group descriptors inode */
     52 #define EXT2_JOURNAL_INO	 8	/* Journal inode */
     53 #define EXT2_EXCLUDE_INO	 9	/* The "exclude" inode, for snapshots */
     54 #define EXT4_REPLICA_INO	10	/* Used by non-upstream feature */
     55 
     56 /* First non-reserved inode for old ext2 filesystems */
     57 #define EXT2_GOOD_OLD_FIRST_INO	11
     58 
     59 /*
     60  * The second extended file system magic number
     61  */
     62 #define EXT2_SUPER_MAGIC	0xEF53
     63 
     64 #ifdef __KERNEL__
     65 #define EXT2_SB(sb)	(&((sb)->u.ext2_sb))
     66 #else
     67 /* Assume that user mode programs are passing in an ext2fs superblock, not
     68  * a kernel struct super_block.  This will allow us to call the feature-test
     69  * macros from user land. */
     70 #define EXT2_SB(sb)	(sb)
     71 #endif
     72 
     73 /*
     74  * Maximal count of links to a file
     75  */
     76 #define EXT2_LINK_MAX		65000
     77 
     78 /*
     79  * Macro-instructions used to manage several block sizes
     80  */
     81 #define EXT2_MIN_BLOCK_LOG_SIZE		10	/* 1024 */
     82 #define EXT2_MAX_BLOCK_LOG_SIZE		16	/* 65536 */
     83 #define EXT2_MIN_BLOCK_SIZE	(1 << EXT2_MIN_BLOCK_LOG_SIZE)
     84 #define EXT2_MAX_BLOCK_SIZE	(1 << EXT2_MAX_BLOCK_LOG_SIZE)
     85 #ifdef __KERNEL__
     86 #define EXT2_BLOCK_SIZE(s)	((s)->s_blocksize)
     87 #define EXT2_BLOCK_SIZE_BITS(s)	((s)->s_blocksize_bits)
     88 #define EXT2_ADDR_PER_BLOCK_BITS(s)	(EXT2_SB(s)->addr_per_block_bits)
     89 #define EXT2_INODE_SIZE(s)	(EXT2_SB(s)->s_inode_size)
     90 #define EXT2_FIRST_INO(s)	(EXT2_SB(s)->s_first_ino)
     91 #else
     92 #define EXT2_BLOCK_SIZE(s)	(EXT2_MIN_BLOCK_SIZE << (s)->s_log_block_size)
     93 #define EXT2_BLOCK_SIZE_BITS(s)	((s)->s_log_block_size + 10)
     94 #define EXT2_INODE_SIZE(s)	(((s)->s_rev_level == EXT2_GOOD_OLD_REV) ? \
     95 				 EXT2_GOOD_OLD_INODE_SIZE : (s)->s_inode_size)
     96 #define EXT2_FIRST_INO(s)	(((s)->s_rev_level == EXT2_GOOD_OLD_REV) ? \
     97 				 EXT2_GOOD_OLD_FIRST_INO : (s)->s_first_ino)
     98 #endif
     99 #define EXT2_ADDR_PER_BLOCK(s)	(EXT2_BLOCK_SIZE(s) / sizeof(__u32))
    100 
    101 /*
    102  * Macro-instructions used to manage allocation clusters
    103  */
    104 #define EXT2_MIN_CLUSTER_LOG_SIZE	EXT2_MIN_BLOCK_LOG_SIZE
    105 #define EXT2_MAX_CLUSTER_LOG_SIZE	29	/* 512MB  */
    106 #define EXT2_MIN_CLUSTER_SIZE		EXT2_MIN_BLOCK_SIZE
    107 #define EXT2_MAX_CLUSTER_SIZE		(1 << EXT2_MAX_CLUSTER_LOG_SIZE)
    108 #define EXT2_CLUSTER_SIZE(s)		(EXT2_MIN_BLOCK_SIZE << \
    109 						(s)->s_log_cluster_size)
    110 #define EXT2_CLUSTER_SIZE_BITS(s)	((s)->s_log_cluster_size + 10)
    111 
    112 /*
    113  * Macro-instructions used to manage fragments
    114  *
    115  * Note: for backwards compatibility only, for the dump program.
    116  * Ext2/3/4 will never support fragments....
    117  */
    118 #define EXT2_MIN_FRAG_SIZE              EXT2_MIN_BLOCK_SIZE
    119 #define EXT2_MAX_FRAG_SIZE              EXT2_MAX_BLOCK_SIZE
    120 #define EXT2_MIN_FRAG_LOG_SIZE          EXT2_MIN_BLOCK_LOG_SIZE
    121 #define EXT2_FRAG_SIZE(s)		EXT2_BLOCK_SIZE(s)
    122 #define EXT2_FRAGS_PER_BLOCK(s)		1
    123 
    124 /*
    125  * ACL structures
    126  */
    127 struct ext2_acl_header	/* Header of Access Control Lists */
    128 {
    129 	__u32	aclh_size;
    130 	__u32	aclh_file_count;
    131 	__u32	aclh_acle_count;
    132 	__u32	aclh_first_acle;
    133 };
    134 
    135 struct ext2_acl_entry	/* Access Control List Entry */
    136 {
    137 	__u32	acle_size;
    138 	__u16	acle_perms;	/* Access permissions */
    139 	__u16	acle_type;	/* Type of entry */
    140 	__u16	acle_tag;	/* User or group identity */
    141 	__u16	acle_pad1;
    142 	__u32	acle_next;	/* Pointer on next entry for the */
    143 					/* same inode or on next free entry */
    144 };
    145 
    146 /*
    147  * Structure of a blocks group descriptor
    148  */
    149 struct ext2_group_desc
    150 {
    151 	__u32	bg_block_bitmap;	/* Blocks bitmap block */
    152 	__u32	bg_inode_bitmap;	/* Inodes bitmap block */
    153 	__u32	bg_inode_table;		/* Inodes table block */
    154 	__u16	bg_free_blocks_count;	/* Free blocks count */
    155 	__u16	bg_free_inodes_count;	/* Free inodes count */
    156 	__u16	bg_used_dirs_count;	/* Directories count */
    157 	__u16	bg_flags;
    158 	__u32	bg_exclude_bitmap_lo;	/* Exclude bitmap for snapshots */
    159 	__u16	bg_block_bitmap_csum_lo;/* crc32c(s_uuid+grp_num+bitmap) LSB */
    160 	__u16	bg_inode_bitmap_csum_lo;/* crc32c(s_uuid+grp_num+bitmap) LSB */
    161 	__u16	bg_itable_unused;	/* Unused inodes count */
    162 	__u16	bg_checksum;		/* crc16(s_uuid+group_num+group_desc)*/
    163 };
    164 
    165 /*
    166  * Structure of a blocks group descriptor
    167  */
    168 struct ext4_group_desc
    169 {
    170 	__u32	bg_block_bitmap;	/* Blocks bitmap block */
    171 	__u32	bg_inode_bitmap;	/* Inodes bitmap block */
    172 	__u32	bg_inode_table;		/* Inodes table block */
    173 	__u16	bg_free_blocks_count;	/* Free blocks count */
    174 	__u16	bg_free_inodes_count;	/* Free inodes count */
    175 	__u16	bg_used_dirs_count;	/* Directories count */
    176 	__u16	bg_flags;		/* EXT4_BG_flags (INODE_UNINIT, etc) */
    177 	__u32	bg_exclude_bitmap_lo;	/* Exclude bitmap for snapshots */
    178 	__u16	bg_block_bitmap_csum_lo;/* crc32c(s_uuid+grp_num+bitmap) LSB */
    179 	__u16	bg_inode_bitmap_csum_lo;/* crc32c(s_uuid+grp_num+bitmap) LSB */
    180 	__u16	bg_itable_unused;	/* Unused inodes count */
    181 	__u16	bg_checksum;		/* crc16(sb_uuid+group+desc) */
    182 	__u32	bg_block_bitmap_hi;	/* Blocks bitmap block MSB */
    183 	__u32	bg_inode_bitmap_hi;	/* Inodes bitmap block MSB */
    184 	__u32	bg_inode_table_hi;	/* Inodes table block MSB */
    185 	__u16	bg_free_blocks_count_hi;/* Free blocks count MSB */
    186 	__u16	bg_free_inodes_count_hi;/* Free inodes count MSB */
    187 	__u16	bg_used_dirs_count_hi;	/* Directories count MSB */
    188 	__u16	bg_itable_unused_hi;	/* Unused inodes count MSB */
    189 	__u32	bg_exclude_bitmap_hi;	/* Exclude bitmap block MSB */
    190 	__u16	bg_block_bitmap_csum_hi;/* crc32c(s_uuid+grp_num+bitmap) MSB */
    191 	__u16	bg_inode_bitmap_csum_hi;/* crc32c(s_uuid+grp_num+bitmap) MSB */
    192 	__u32	bg_reserved;
    193 };
    194 
    195 #define EXT2_BG_INODE_UNINIT	0x0001 /* Inode table/bitmap not initialized */
    196 #define EXT2_BG_BLOCK_UNINIT	0x0002 /* Block bitmap not initialized */
    197 #define EXT2_BG_INODE_ZEROED	0x0004 /* On-disk itable initialized to zero */
    198 
    199 /*
    200  * Data structures used by the directory indexing feature
    201  *
    202  * Note: all of the multibyte integer fields are little endian.
    203  */
    204 
    205 /*
    206  * Note: dx_root_info is laid out so that if it should somehow get
    207  * overlaid by a dirent the two low bits of the hash version will be
    208  * zero.  Therefore, the hash version mod 4 should never be 0.
    209  * Sincerely, the paranoia department.
    210  */
    211 struct ext2_dx_root_info {
    212 	__u32 reserved_zero;
    213 	__u8 hash_version; /* 0 now, 1 at release */
    214 	__u8 info_length; /* 8 */
    215 	__u8 indirect_levels;
    216 	__u8 unused_flags;
    217 };
    218 
    219 #define EXT2_HASH_LEGACY		0
    220 #define EXT2_HASH_HALF_MD4		1
    221 #define EXT2_HASH_TEA			2
    222 #define EXT2_HASH_LEGACY_UNSIGNED	3 /* reserved for userspace lib */
    223 #define EXT2_HASH_HALF_MD4_UNSIGNED	4 /* reserved for userspace lib */
    224 #define EXT2_HASH_TEA_UNSIGNED		5 /* reserved for userspace lib */
    225 
    226 #define EXT2_HASH_FLAG_INCOMPAT	0x1
    227 
    228 struct ext2_dx_entry {
    229 	__u32 hash;
    230 	__u32 block;
    231 };
    232 
    233 struct ext2_dx_countlimit {
    234 	__u16 limit;
    235 	__u16 count;
    236 };
    237 
    238 
    239 /*
    240  * Macro-instructions used to manage group descriptors
    241  */
    242 #define EXT2_MIN_DESC_SIZE             32
    243 #define EXT2_MIN_DESC_SIZE_64BIT       64
    244 #define EXT2_MAX_DESC_SIZE             EXT2_MIN_BLOCK_SIZE
    245 #define EXT2_DESC_SIZE(s)                                                \
    246        ((EXT2_SB(s)->s_feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT) ? \
    247 	(s)->s_desc_size : EXT2_MIN_DESC_SIZE)
    248 
    249 #define EXT2_BLOCKS_PER_GROUP(s)	(EXT2_SB(s)->s_blocks_per_group)
    250 #define EXT2_INODES_PER_GROUP(s)	(EXT2_SB(s)->s_inodes_per_group)
    251 #define EXT2_CLUSTERS_PER_GROUP(s)	(EXT2_SB(s)->s_clusters_per_group)
    252 #define EXT2_INODES_PER_BLOCK(s)	(EXT2_BLOCK_SIZE(s)/EXT2_INODE_SIZE(s))
    253 /* limits imposed by 16-bit value gd_free_{blocks,inode}_count */
    254 #define EXT2_MAX_BLOCKS_PER_GROUP(s)	((((unsigned) 1 << 16) - 8) *	\
    255 					 (EXT2_CLUSTER_SIZE(s) / \
    256 					  EXT2_BLOCK_SIZE(s)))
    257 #define EXT2_MAX_CLUSTERS_PER_GROUP(s)	(((unsigned) 1 << 16) - 8)
    258 #define EXT2_MAX_INODES_PER_GROUP(s)	(((unsigned) 1 << 16) - \
    259 					 EXT2_INODES_PER_BLOCK(s))
    260 #ifdef __KERNEL__
    261 #define EXT2_DESC_PER_BLOCK(s)		(EXT2_SB(s)->s_desc_per_block)
    262 #define EXT2_DESC_PER_BLOCK_BITS(s)	(EXT2_SB(s)->s_desc_per_block_bits)
    263 #else
    264 #define EXT2_DESC_PER_BLOCK(s)		(EXT2_BLOCK_SIZE(s) / EXT2_DESC_SIZE(s))
    265 #endif
    266 
    267 /*
    268  * Constants relative to the data blocks
    269  */
    270 #define EXT2_NDIR_BLOCKS		12
    271 #define EXT2_IND_BLOCK			EXT2_NDIR_BLOCKS
    272 #define EXT2_DIND_BLOCK			(EXT2_IND_BLOCK + 1)
    273 #define EXT2_TIND_BLOCK			(EXT2_DIND_BLOCK + 1)
    274 #define EXT2_N_BLOCKS			(EXT2_TIND_BLOCK + 1)
    275 
    276 /*
    277  * Inode flags
    278  */
    279 #define EXT2_SECRM_FL			0x00000001 /* Secure deletion */
    280 #define EXT2_UNRM_FL			0x00000002 /* Undelete */
    281 #define EXT2_COMPR_FL			0x00000004 /* Compress file */
    282 #define EXT2_SYNC_FL			0x00000008 /* Synchronous updates */
    283 #define EXT2_IMMUTABLE_FL		0x00000010 /* Immutable file */
    284 #define EXT2_APPEND_FL			0x00000020 /* writes to file may only append */
    285 #define EXT2_NODUMP_FL			0x00000040 /* do not dump file */
    286 #define EXT2_NOATIME_FL			0x00000080 /* do not update atime */
    287 /* Reserved for compression usage... */
    288 #define EXT2_DIRTY_FL			0x00000100
    289 #define EXT2_COMPRBLK_FL		0x00000200 /* One or more compressed clusters */
    290 #define EXT2_NOCOMPR_FL			0x00000400 /* Access raw compressed data */
    291 	/* nb: was previously EXT2_ECOMPR_FL */
    292 #define EXT4_ENCRYPT_FL			0x00000800 /* encrypted inode */
    293 /* End compression flags --- maybe not all used */
    294 #define EXT2_BTREE_FL			0x00001000 /* btree format dir */
    295 #define EXT2_INDEX_FL			0x00001000 /* hash-indexed directory */
    296 #define EXT2_IMAGIC_FL			0x00002000
    297 #define EXT3_JOURNAL_DATA_FL		0x00004000 /* file data should be journaled */
    298 #define EXT2_NOTAIL_FL			0x00008000 /* file tail should not be merged */
    299 #define EXT2_DIRSYNC_FL 		0x00010000 /* Synchronous directory modifications */
    300 #define EXT2_TOPDIR_FL			0x00020000 /* Top of directory hierarchies*/
    301 #define EXT4_HUGE_FILE_FL               0x00040000 /* Set to each huge file */
    302 #define EXT4_EXTENTS_FL 		0x00080000 /* Inode uses extents */
    303 #define EXT4_EA_INODE_FL	        0x00200000 /* Inode used for large EA */
    304 /* EXT4_EOFBLOCKS_FL 0x00400000 was here */
    305 #define FS_NOCOW_FL			0x00800000 /* Do not cow file */
    306 #define EXT4_SNAPFILE_FL		0x01000000  /* Inode is a snapshot */
    307 #define EXT4_SNAPFILE_DELETED_FL	0x04000000  /* Snapshot is being deleted */
    308 #define EXT4_SNAPFILE_SHRUNK_FL		0x08000000  /* Snapshot shrink has completed */
    309 #define EXT2_RESERVED_FL		0x80000000 /* reserved for ext2 lib */
    310 
    311 #define EXT2_FL_USER_VISIBLE		0x004BDFFF /* User visible flags */
    312 #define EXT2_FL_USER_MODIFIABLE		0x004B80FF /* User modifiable flags */
    313 
    314 /*
    315  * ioctl commands
    316  */
    317 
    318 /* Used for online resize */
    319 struct ext2_new_group_input {
    320 	__u32 group;		/* Group number for this data */
    321 	__u32 block_bitmap;	/* Absolute block number of block bitmap */
    322 	__u32 inode_bitmap;	/* Absolute block number of inode bitmap */
    323 	__u32 inode_table;	/* Absolute block number of inode table start */
    324 	__u32 blocks_count;	/* Total number of blocks in this group */
    325 	__u16 reserved_blocks;	/* Number of reserved blocks in this group */
    326 	__u16 unused;		/* Number of reserved GDT blocks in group */
    327 };
    328 
    329 struct ext4_new_group_input {
    330 	__u32 group;		/* Group number for this data */
    331 	__u64 block_bitmap;	/* Absolute block number of block bitmap */
    332 	__u64 inode_bitmap;	/* Absolute block number of inode bitmap */
    333 	__u64 inode_table;	/* Absolute block number of inode table start */
    334 	__u32 blocks_count;	/* Total number of blocks in this group */
    335 	__u16 reserved_blocks;	/* Number of reserved blocks in this group */
    336 	__u16 unused;
    337 };
    338 
    339 #ifdef __GNU__			/* Needed for the Hurd */
    340 #define _IOT_ext2_new_group_input _IOT (_IOTS(__u32), 5, _IOTS(__u16), 2, 0, 0)
    341 #endif
    342 
    343 #define EXT2_IOC_GETFLAGS		_IOR('f', 1, long)
    344 #define EXT2_IOC_SETFLAGS		_IOW('f', 2, long)
    345 #define EXT2_IOC_GETVERSION		_IOR('v', 1, long)
    346 #define EXT2_IOC_SETVERSION		_IOW('v', 2, long)
    347 #define EXT2_IOC_GETVERSION_NEW		_IOR('f', 3, long)
    348 #define EXT2_IOC_SETVERSION_NEW		_IOW('f', 4, long)
    349 #define EXT2_IOC_GROUP_EXTEND		_IOW('f', 7, unsigned long)
    350 #define EXT2_IOC_GROUP_ADD		_IOW('f', 8,struct ext2_new_group_input)
    351 #define EXT4_IOC_GROUP_ADD		_IOW('f', 8,struct ext4_new_group_input)
    352 #define EXT4_IOC_RESIZE_FS		_IOW('f', 16, __u64)
    353 
    354 /*
    355  * Structure of an inode on the disk
    356  */
    357 struct ext2_inode {
    358 	__u16	i_mode;		/* File mode */
    359 	__u16	i_uid;		/* Low 16 bits of Owner Uid */
    360 	__u32	i_size;		/* Size in bytes */
    361 	__u32	i_atime;	/* Access time */
    362 	__u32	i_ctime;	/* Inode change time */
    363 	__u32	i_mtime;	/* Modification time */
    364 	__u32	i_dtime;	/* Deletion Time */
    365 	__u16	i_gid;		/* Low 16 bits of Group Id */
    366 	__u16	i_links_count;	/* Links count */
    367 	__u32	i_blocks;	/* Blocks count */
    368 	__u32	i_flags;	/* File flags */
    369 	union {
    370 		struct {
    371 			__u32	l_i_version; /* was l_i_reserved1 */
    372 		} linux1;
    373 		struct {
    374 			__u32  h_i_translator;
    375 		} hurd1;
    376 	} osd1;				/* OS dependent 1 */
    377 	__u32	i_block[EXT2_N_BLOCKS];/* Pointers to blocks */
    378 	__u32	i_generation;	/* File version (for NFS) */
    379 	__u32	i_file_acl;	/* File ACL */
    380 	__u32	i_size_high;	/* Formerly i_dir_acl, directory ACL */
    381 	__u32	i_faddr;	/* Fragment address */
    382 	union {
    383 		struct {
    384 			__u16	l_i_blocks_hi;
    385 			__u16	l_i_file_acl_high;
    386 			__u16	l_i_uid_high;	/* these 2 fields    */
    387 			__u16	l_i_gid_high;	/* were reserved2[0] */
    388 			__u16	l_i_checksum_lo; /* crc32c(uuid+inum+inode) */
    389 			__u16	l_i_reserved;
    390 		} linux2;
    391 		struct {
    392 			__u8	h_i_frag;	/* Fragment number */
    393 			__u8	h_i_fsize;	/* Fragment size */
    394 			__u16	h_i_mode_high;
    395 			__u16	h_i_uid_high;
    396 			__u16	h_i_gid_high;
    397 			__u32	h_i_author;
    398 		} hurd2;
    399 	} osd2;				/* OS dependent 2 */
    400 };
    401 
    402 /*
    403  * Permanent part of an large inode on the disk
    404  */
    405 struct ext2_inode_large {
    406 	__u16	i_mode;		/* File mode */
    407 	__u16	i_uid;		/* Low 16 bits of Owner Uid */
    408 	__u32	i_size;		/* Size in bytes */
    409 	__u32	i_atime;	/* Access time */
    410 	__u32	i_ctime;	/* Inode Change time */
    411 	__u32	i_mtime;	/* Modification time */
    412 	__u32	i_dtime;	/* Deletion Time */
    413 	__u16	i_gid;		/* Low 16 bits of Group Id */
    414 	__u16	i_links_count;	/* Links count */
    415 	__u32	i_blocks;	/* Blocks count */
    416 	__u32	i_flags;	/* File flags */
    417 	union {
    418 		struct {
    419 			__u32	l_i_version; /* was l_i_reserved1 */
    420 		} linux1;
    421 		struct {
    422 			__u32  h_i_translator;
    423 		} hurd1;
    424 	} osd1;				/* OS dependent 1 */
    425 	__u32	i_block[EXT2_N_BLOCKS];/* Pointers to blocks */
    426 	__u32	i_generation;	/* File version (for NFS) */
    427 	__u32	i_file_acl;	/* File ACL */
    428 	__u32	i_size_high;	/* Formerly i_dir_acl, directory ACL */
    429 	__u32	i_faddr;	/* Fragment address */
    430 	union {
    431 		struct {
    432 			__u16	l_i_blocks_hi;
    433 			__u16	l_i_file_acl_high;
    434 			__u16	l_i_uid_high;	/* these 2 fields    */
    435 			__u16	l_i_gid_high;	/* were reserved2[0] */
    436 			__u16	l_i_checksum_lo; /* crc32c(uuid+inum+inode) */
    437 			__u16	l_i_reserved;
    438 		} linux2;
    439 		struct {
    440 			__u8	h_i_frag;	/* Fragment number */
    441 			__u8	h_i_fsize;	/* Fragment size */
    442 			__u16	h_i_mode_high;
    443 			__u16	h_i_uid_high;
    444 			__u16	h_i_gid_high;
    445 			__u32	h_i_author;
    446 		} hurd2;
    447 	} osd2;				/* OS dependent 2 */
    448 	__u16	i_extra_isize;
    449 	__u16	i_checksum_hi;	/* crc32c(uuid+inum+inode) */
    450 	__u32	i_ctime_extra;	/* extra Change time (nsec << 2 | epoch) */
    451 	__u32	i_mtime_extra;	/* extra Modification time (nsec << 2 | epoch) */
    452 	__u32	i_atime_extra;	/* extra Access time (nsec << 2 | epoch) */
    453 	__u32	i_crtime;	/* File creation time */
    454 	__u32	i_crtime_extra;	/* extra File creation time (nsec << 2 | epoch)*/
    455 	__u32	i_version_hi;	/* high 32 bits for 64-bit version */
    456 };
    457 
    458 #define i_dir_acl	i_size_high
    459 
    460 #if defined(__KERNEL__) || defined(__linux__)
    461 #define i_reserved1	osd1.linux1.l_i_reserved1
    462 #define i_frag		osd2.linux2.l_i_frag
    463 #define i_fsize		osd2.linux2.l_i_fsize
    464 #define i_uid_low	i_uid
    465 #define i_gid_low	i_gid
    466 #define i_uid_high	osd2.linux2.l_i_uid_high
    467 #define i_gid_high	osd2.linux2.l_i_gid_high
    468 #else
    469 #if defined(__GNU__)
    470 
    471 #define i_translator	osd1.hurd1.h_i_translator
    472 #define i_frag		osd2.hurd2.h_i_frag;
    473 #define i_fsize		osd2.hurd2.h_i_fsize;
    474 #define i_uid_high	osd2.hurd2.h_i_uid_high
    475 #define i_gid_high	osd2.hurd2.h_i_gid_high
    476 #define i_author	osd2.hurd2.h_i_author
    477 
    478 #endif  /* __GNU__ */
    479 #endif	/* defined(__KERNEL__) || defined(__linux__) */
    480 
    481 #define inode_uid(inode)	((inode).i_uid | (inode).osd2.linux2.l_i_uid_high << 16)
    482 #define inode_gid(inode)	((inode).i_gid | (inode).osd2.linux2.l_i_gid_high << 16)
    483 #define ext2fs_set_i_uid_high(inode,x) ((inode).osd2.linux2.l_i_uid_high = (x))
    484 #define ext2fs_set_i_gid_high(inode,x) ((inode).osd2.linux2.l_i_gid_high = (x))
    485 
    486 /*
    487  * File system states
    488  */
    489 #define EXT2_VALID_FS			0x0001	/* Unmounted cleanly */
    490 #define EXT2_ERROR_FS			0x0002	/* Errors detected */
    491 #define EXT3_ORPHAN_FS			0x0004	/* Orphans being recovered */
    492 
    493 /*
    494  * Misc. filesystem flags
    495  */
    496 #define EXT2_FLAGS_SIGNED_HASH		0x0001  /* Signed dirhash in use */
    497 #define EXT2_FLAGS_UNSIGNED_HASH	0x0002  /* Unsigned dirhash in use */
    498 #define EXT2_FLAGS_TEST_FILESYS		0x0004	/* OK for use on development code */
    499 #define EXT2_FLAGS_IS_SNAPSHOT		0x0010	/* This is a snapshot image */
    500 #define EXT2_FLAGS_FIX_SNAPSHOT		0x0020	/* Snapshot inodes corrupted */
    501 #define EXT2_FLAGS_FIX_EXCLUDE		0x0040	/* Exclude bitmaps corrupted */
    502 
    503 /*
    504  * Mount flags
    505  */
    506 #define EXT2_MOUNT_CHECK		0x0001	/* Do mount-time checks */
    507 #define EXT2_MOUNT_GRPID		0x0004	/* Create files with directory's group */
    508 #define EXT2_MOUNT_DEBUG		0x0008	/* Some debugging messages */
    509 #define EXT2_MOUNT_ERRORS_CONT		0x0010	/* Continue on errors */
    510 #define EXT2_MOUNT_ERRORS_RO		0x0020	/* Remount fs ro on errors */
    511 #define EXT2_MOUNT_ERRORS_PANIC		0x0040	/* Panic on errors */
    512 #define EXT2_MOUNT_MINIX_DF		0x0080	/* Mimics the Minix statfs */
    513 #define EXT2_MOUNT_NO_UID32		0x0200  /* Disable 32-bit UIDs */
    514 
    515 #define clear_opt(o, opt)		o &= ~EXT2_MOUNT_##opt
    516 #define set_opt(o, opt)			o |= EXT2_MOUNT_##opt
    517 #define test_opt(sb, opt)		(EXT2_SB(sb)->s_mount_opt & \
    518 					 EXT2_MOUNT_##opt)
    519 /*
    520  * Maximal mount counts between two filesystem checks
    521  */
    522 #define EXT2_DFL_MAX_MNT_COUNT		20	/* Allow 20 mounts */
    523 #define EXT2_DFL_CHECKINTERVAL		0	/* Don't use interval check */
    524 
    525 /*
    526  * Behaviour when detecting errors
    527  */
    528 #define EXT2_ERRORS_CONTINUE		1	/* Continue execution */
    529 #define EXT2_ERRORS_RO			2	/* Remount fs read-only */
    530 #define EXT2_ERRORS_PANIC		3	/* Panic */
    531 #define EXT2_ERRORS_DEFAULT		EXT2_ERRORS_CONTINUE
    532 
    533 #if (__GNUC__ >= 4)
    534 #define ext4_offsetof(TYPE,MEMBER) __builtin_offsetof(TYPE,MEMBER)
    535 #else
    536 #define ext4_offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
    537 #endif
    538 
    539 /* Encryption algorithms, key size and key reference len */
    540 #define EXT4_ENCRYPTION_MODE_INVALID		0
    541 #define EXT4_ENCRYPTION_MODE_AES_256_XTS	1
    542 #define EXT4_ENCRYPTION_MODE_AES_256_GCM	2
    543 #define EXT4_ENCRYPTION_MODE_AES_256_CBC	3
    544 #define EXT4_ENCRYPTION_MODE_AES_256_CTS	4
    545 
    546 #define EXT4_AES_256_XTS_KEY_SIZE		64
    547 #define EXT4_AES_256_GCM_KEY_SIZE		32
    548 #define EXT4_AES_256_CBC_KEY_SIZE		32
    549 #define EXT4_AES_256_CTS_KEY_SIZE		32
    550 #define EXT4_MAX_KEY_SIZE			64
    551 
    552 #define EXT4_KEY_DESCRIPTOR_SIZE		8
    553 #define EXT4_CRYPTO_BLOCK_SIZE			16
    554 
    555 /* Password derivation constants */
    556 #define EXT4_MAX_PASSPHRASE_SIZE		1024
    557 #define EXT4_MAX_SALT_SIZE			256
    558 #define EXT4_PBKDF2_ITERATIONS			0xFFFF
    559 
    560 /*
    561  * Policy provided via an ioctl on the topmost directory. This
    562  * structure is also in the kernel.
    563  */
    564 struct ext4_encryption_policy {
    565   char version;
    566   char contents_encryption_mode;
    567   char filenames_encryption_mode;
    568   char flags;
    569   char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
    570 } __attribute__((__packed__));
    571 
    572 struct ext4_encryption_key {
    573         __u32 mode;
    574         char raw[EXT4_MAX_KEY_SIZE];
    575         __u32 size;
    576 } __attribute__((__packed__));
    577 
    578 /*
    579  * Structure of the super block
    580  */
    581 struct ext2_super_block {
    582 	__u32	s_inodes_count;		/* Inodes count */
    583 	__u32	s_blocks_count;		/* Blocks count */
    584 	__u32	s_r_blocks_count;	/* Reserved blocks count */
    585 	__u32	s_free_blocks_count;	/* Free blocks count */
    586 	__u32	s_free_inodes_count;	/* Free inodes count */
    587 	__u32	s_first_data_block;	/* First Data Block */
    588 	__u32	s_log_block_size;	/* Block size */
    589 	__u32	s_log_cluster_size;	/* Allocation cluster size */
    590 	__u32	s_blocks_per_group;	/* # Blocks per group */
    591 	__u32	s_clusters_per_group;	/* # Fragments per group */
    592 	__u32	s_inodes_per_group;	/* # Inodes per group */
    593 	__u32	s_mtime;		/* Mount time */
    594 	__u32	s_wtime;		/* Write time */
    595 	__u16	s_mnt_count;		/* Mount count */
    596 	__s16	s_max_mnt_count;	/* Maximal mount count */
    597 	__u16	s_magic;		/* Magic signature */
    598 	__u16	s_state;		/* File system state */
    599 	__u16	s_errors;		/* Behaviour when detecting errors */
    600 	__u16	s_minor_rev_level;	/* minor revision level */
    601 	__u32	s_lastcheck;		/* time of last check */
    602 	__u32	s_checkinterval;	/* max. time between checks */
    603 	__u32	s_creator_os;		/* OS */
    604 	__u32	s_rev_level;		/* Revision level */
    605 	__u16	s_def_resuid;		/* Default uid for reserved blocks */
    606 	__u16	s_def_resgid;		/* Default gid for reserved blocks */
    607 	/*
    608 	 * These fields are for EXT2_DYNAMIC_REV superblocks only.
    609 	 *
    610 	 * Note: the difference between the compatible feature set and
    611 	 * the incompatible feature set is that if there is a bit set
    612 	 * in the incompatible feature set that the kernel doesn't
    613 	 * know about, it should refuse to mount the filesystem.
    614 	 *
    615 	 * e2fsck's requirements are more strict; if it doesn't know
    616 	 * about a feature in either the compatible or incompatible
    617 	 * feature set, it must abort and not try to meddle with
    618 	 * things it doesn't understand...
    619 	 */
    620 	__u32	s_first_ino;		/* First non-reserved inode */
    621 	__u16   s_inode_size;		/* size of inode structure */
    622 	__u16	s_block_group_nr;	/* block group # of this superblock */
    623 	__u32	s_feature_compat;	/* compatible feature set */
    624 	__u32	s_feature_incompat;	/* incompatible feature set */
    625 	__u32	s_feature_ro_compat;	/* readonly-compatible feature set */
    626 	__u8	s_uuid[16];		/* 128-bit uuid for volume */
    627 	char	s_volume_name[16];	/* volume name */
    628 	char	s_last_mounted[64];	/* directory where last mounted */
    629 	__u32	s_algorithm_usage_bitmap; /* For compression */
    630 	/*
    631 	 * Performance hints.  Directory preallocation should only
    632 	 * happen if the EXT2_FEATURE_COMPAT_DIR_PREALLOC flag is on.
    633 	 */
    634 	__u8	s_prealloc_blocks;	/* Nr of blocks to try to preallocate*/
    635 	__u8	s_prealloc_dir_blocks;	/* Nr to preallocate for dirs */
    636 	__u16	s_reserved_gdt_blocks;	/* Per group table for online growth */
    637 	/*
    638 	 * Journaling support valid if EXT2_FEATURE_COMPAT_HAS_JOURNAL set.
    639 	 */
    640 	__u8	s_journal_uuid[16];	/* uuid of journal superblock */
    641 	__u32	s_journal_inum;		/* inode number of journal file */
    642 	__u32	s_journal_dev;		/* device number of journal file */
    643 	__u32	s_last_orphan;		/* start of list of inodes to delete */
    644 	__u32	s_hash_seed[4];		/* HTREE hash seed */
    645 	__u8	s_def_hash_version;	/* Default hash version to use */
    646 	__u8	s_jnl_backup_type; 	/* Default type of journal backup */
    647 	__u16	s_desc_size;		/* Group desc. size: INCOMPAT_64BIT */
    648 	__u32	s_default_mount_opts;
    649 	__u32	s_first_meta_bg;	/* First metablock group */
    650 	__u32	s_mkfs_time;		/* When the filesystem was created */
    651 	__u32	s_jnl_blocks[17]; 	/* Backup of the journal inode */
    652 	__u32	s_blocks_count_hi;	/* Blocks count high 32bits */
    653 	__u32	s_r_blocks_count_hi;	/* Reserved blocks count high 32 bits*/
    654 	__u32	s_free_blocks_hi; 	/* Free blocks count */
    655 	__u16	s_min_extra_isize;	/* All inodes have at least # bytes */
    656 	__u16	s_want_extra_isize; 	/* New inodes should reserve # bytes */
    657 	__u32	s_flags;		/* Miscellaneous flags */
    658 	__u16   s_raid_stride;		/* RAID stride */
    659 	__u16   s_mmp_update_interval;  /* # seconds to wait in MMP checking */
    660 	__u64   s_mmp_block;            /* Block for multi-mount protection */
    661 	__u32   s_raid_stripe_width;    /* blocks on all data disks (N*stride)*/
    662 	__u8	s_log_groups_per_flex;	/* FLEX_BG group size */
    663 	__u8    s_checksum_type;	/* metadata checksum algorithm */
    664 	__u8	s_encryption_level;	/* versioning level for encryption */
    665 	__u8	s_reserved_pad;		/* Padding to next 32bits */
    666 	__u64	s_kbytes_written;	/* nr of lifetime kilobytes written */
    667 	__u32	s_snapshot_inum;	/* Inode number of active snapshot */
    668 	__u32	s_snapshot_id;		/* sequential ID of active snapshot */
    669 	__u64	s_snapshot_r_blocks_count; /* reserved blocks for active
    670 					      snapshot's future use */
    671 	__u32	s_snapshot_list;	/* inode number of the head of the on-disk snapshot list */
    672 #define EXT4_S_ERR_START ext4_offsetof(struct ext2_super_block, s_error_count)
    673 	__u32	s_error_count;		/* number of fs errors */
    674 	__u32	s_first_error_time;	/* first time an error happened */
    675 	__u32	s_first_error_ino;	/* inode involved in first error */
    676 	__u64	s_first_error_block;	/* block involved of first error */
    677 	__u8	s_first_error_func[32];	/* function where the error happened */
    678 	__u32	s_first_error_line;	/* line number where error happened */
    679 	__u32	s_last_error_time;	/* most recent time of an error */
    680 	__u32	s_last_error_ino;	/* inode involved in last error */
    681 	__u32	s_last_error_line;	/* line number where error happened */
    682 	__u64	s_last_error_block;	/* block involved of last error */
    683 	__u8	s_last_error_func[32];	/* function where the error happened */
    684 #define EXT4_S_ERR_END ext4_offsetof(struct ext2_super_block, s_mount_opts)
    685 	__u8	s_mount_opts[64];
    686 	__u32	s_usr_quota_inum;	/* inode number of user quota file */
    687 	__u32	s_grp_quota_inum;	/* inode number of group quota file */
    688 	__u32	s_overhead_blocks;	/* overhead blocks/clusters in fs */
    689 	__u32	s_backup_bgs[2];	/* If sparse_super2 enabled */
    690 	__u8	s_encrypt_algos[4];	/* Encryption algorithms in use  */
    691 	__u8	s_encrypt_pw_salt[16];	/* Salt used for string2key algorithm */
    692 	__u32	s_lpf_ino;		/* Location of the lost+found inode */
    693 	__u32   s_reserved[100];        /* Padding to the end of the block */
    694 	__u32	s_checksum;		/* crc32c(superblock) */
    695 };
    696 
    697 #define EXT4_S_ERR_LEN (EXT4_S_ERR_END - EXT4_S_ERR_START)
    698 
    699 /*
    700  * Codes for operating systems
    701  */
    702 #define EXT2_OS_LINUX		0
    703 #define EXT2_OS_HURD		1
    704 #define EXT2_OBSO_OS_MASIX	2
    705 #define EXT2_OS_FREEBSD		3
    706 #define EXT2_OS_LITES		4
    707 
    708 /*
    709  * Revision levels
    710  */
    711 #define EXT2_GOOD_OLD_REV	0	/* The good old (original) format */
    712 #define EXT2_DYNAMIC_REV	1	/* V2 format w/ dynamic inode sizes */
    713 
    714 #define EXT2_CURRENT_REV	EXT2_GOOD_OLD_REV
    715 #define EXT2_MAX_SUPP_REV	EXT2_DYNAMIC_REV
    716 
    717 #define EXT2_GOOD_OLD_INODE_SIZE 128
    718 
    719 /*
    720  * Journal inode backup types
    721  */
    722 #define EXT3_JNL_BACKUP_BLOCKS	1
    723 
    724 /*
    725  * Feature set definitions
    726  */
    727 
    728 #define EXT2_HAS_COMPAT_FEATURE(sb,mask)			\
    729 	( EXT2_SB(sb)->s_feature_compat & (mask) )
    730 #define EXT2_HAS_RO_COMPAT_FEATURE(sb,mask)			\
    731 	( EXT2_SB(sb)->s_feature_ro_compat & (mask) )
    732 #define EXT2_HAS_INCOMPAT_FEATURE(sb,mask)			\
    733 	( EXT2_SB(sb)->s_feature_incompat & (mask) )
    734 
    735 #define EXT2_FEATURE_COMPAT_DIR_PREALLOC	0x0001
    736 #define EXT2_FEATURE_COMPAT_IMAGIC_INODES	0x0002
    737 #define EXT3_FEATURE_COMPAT_HAS_JOURNAL		0x0004
    738 #define EXT2_FEATURE_COMPAT_EXT_ATTR		0x0008
    739 #define EXT2_FEATURE_COMPAT_RESIZE_INODE	0x0010
    740 #define EXT2_FEATURE_COMPAT_DIR_INDEX		0x0020
    741 #define EXT2_FEATURE_COMPAT_LAZY_BG		0x0040
    742 /* #define EXT2_FEATURE_COMPAT_EXCLUDE_INODE	0x0080 not used, legacy */
    743 #define EXT2_FEATURE_COMPAT_EXCLUDE_BITMAP	0x0100
    744 
    745 
    746 #define EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER	0x0001
    747 #define EXT2_FEATURE_RO_COMPAT_LARGE_FILE	0x0002
    748 /* #define EXT2_FEATURE_RO_COMPAT_BTREE_DIR	0x0004 not used */
    749 #define EXT4_FEATURE_RO_COMPAT_HUGE_FILE	0x0008
    750 #define EXT4_FEATURE_RO_COMPAT_GDT_CSUM		0x0010
    751 #define EXT4_FEATURE_RO_COMPAT_DIR_NLINK	0x0020
    752 #define EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE	0x0040
    753 #define EXT4_FEATURE_RO_COMPAT_HAS_SNAPSHOT	0x0080
    754 #define EXT4_FEATURE_RO_COMPAT_QUOTA		0x0100
    755 #define EXT4_FEATURE_RO_COMPAT_BIGALLOC		0x0200
    756 #define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM	0x0400
    757 #define EXT4_FEATURE_RO_COMPAT_REPLICA		0x0800
    758 
    759 #define EXT2_FEATURE_INCOMPAT_COMPRESSION	0x0001
    760 #define EXT2_FEATURE_INCOMPAT_FILETYPE		0x0002
    761 #define EXT3_FEATURE_INCOMPAT_RECOVER		0x0004 /* Needs recovery */
    762 #define EXT3_FEATURE_INCOMPAT_JOURNAL_DEV	0x0008 /* Journal device */
    763 #define EXT2_FEATURE_INCOMPAT_META_BG		0x0010
    764 #define EXT3_FEATURE_INCOMPAT_EXTENTS		0x0040
    765 #define EXT4_FEATURE_INCOMPAT_64BIT		0x0080
    766 #define EXT4_FEATURE_INCOMPAT_MMP		0x0100
    767 #define EXT4_FEATURE_INCOMPAT_FLEX_BG		0x0200
    768 #define EXT4_FEATURE_INCOMPAT_EA_INODE		0x0400
    769 #define EXT4_FEATURE_INCOMPAT_DIRDATA		0x1000
    770 /* 0x2000 was EXT4_FEATURE_INCOMPAT_BG_USE_META_CSUM but this was never used */
    771 #define EXT4_FEATURE_INCOMPAT_LARGEDIR		0x4000 /* >2GB or 3-lvl htree */
    772 #define EXT4_FEATURE_INCOMPAT_INLINEDATA	0x8000 /* data in inode */
    773 #define EXT4_FEATURE_INCOMPAT_ENCRYPT		0x10000
    774 
    775 #define EXT2_FEATURE_COMPAT_SUPP	0
    776 #define EXT2_FEATURE_INCOMPAT_SUPP    (EXT2_FEATURE_INCOMPAT_FILETYPE| \
    777 				       EXT4_FEATURE_INCOMPAT_MMP)
    778 #define EXT2_FEATURE_RO_COMPAT_SUPP	(EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER| \
    779 					 EXT2_FEATURE_RO_COMPAT_LARGE_FILE| \
    780 					 EXT4_FEATURE_RO_COMPAT_DIR_NLINK| \
    781 					 EXT2_FEATURE_RO_COMPAT_BTREE_DIR)
    782 
    783 /*
    784  * Default values for user and/or group using reserved blocks
    785  */
    786 #define EXT2_DEF_RESUID		0
    787 #define EXT2_DEF_RESGID		0
    788 
    789 /*
    790  * Default mount options
    791  */
    792 #define EXT2_DEFM_DEBUG		0x0001
    793 #define EXT2_DEFM_BSDGROUPS	0x0002
    794 #define EXT2_DEFM_XATTR_USER	0x0004
    795 #define EXT2_DEFM_ACL		0x0008
    796 #define EXT2_DEFM_UID16		0x0010
    797 #define EXT3_DEFM_JMODE		0x0060
    798 #define EXT3_DEFM_JMODE_DATA	0x0020
    799 #define EXT3_DEFM_JMODE_ORDERED	0x0040
    800 #define EXT3_DEFM_JMODE_WBACK	0x0060
    801 #define EXT4_DEFM_NOBARRIER	0x0100
    802 #define EXT4_DEFM_BLOCK_VALIDITY 0x0200
    803 #define EXT4_DEFM_DISCARD	0x0400
    804 #define EXT4_DEFM_NODELALLOC	0x0800
    805 
    806 /*
    807  * Structure of a directory entry
    808  */
    809 #define EXT2_NAME_LEN 255
    810 
    811 struct ext2_dir_entry {
    812 	__u32	inode;			/* Inode number */
    813 	__u16	rec_len;		/* Directory entry length */
    814 	__u16	name_len;		/* Name length */
    815 	char	name[EXT2_NAME_LEN];	/* File name */
    816 };
    817 
    818 /*
    819  * The new version of the directory entry.  Since EXT2 structures are
    820  * stored in intel byte order, and the name_len field could never be
    821  * bigger than 255 chars, it's safe to reclaim the extra byte for the
    822  * file_type field.
    823  */
    824 struct ext2_dir_entry_2 {
    825 	__u32	inode;			/* Inode number */
    826 	__u16	rec_len;		/* Directory entry length */
    827 	__u8	name_len;		/* Name length */
    828 	__u8	file_type;
    829 	char	name[EXT2_NAME_LEN];	/* File name */
    830 };
    831 
    832 /*
    833  * Ext2 directory file types.  Only the low 3 bits are used.  The
    834  * other bits are reserved for now.
    835  */
    836 #define EXT2_FT_UNKNOWN		0
    837 #define EXT2_FT_REG_FILE	1
    838 #define EXT2_FT_DIR		2
    839 #define EXT2_FT_CHRDEV		3
    840 #define EXT2_FT_BLKDEV		4
    841 #define EXT2_FT_FIFO		5
    842 #define EXT2_FT_SOCK		6
    843 #define EXT2_FT_SYMLINK		7
    844 
    845 #define EXT2_FT_MAX		8
    846 
    847 /*
    848  * EXT2_DIR_PAD defines the directory entries boundaries
    849  *
    850  * NOTE: It must be a multiple of 4
    851  */
    852 #define EXT2_DIR_PAD			4
    853 #define EXT2_DIR_ROUND			(EXT2_DIR_PAD - 1)
    854 #define EXT2_DIR_REC_LEN(name_len)	(((name_len) + 8 + EXT2_DIR_ROUND) & \
    855 					 ~EXT2_DIR_ROUND)
    856 
    857 /*
    858  * This structure is used for multiple mount protection. It is written
    859  * into the block number saved in the s_mmp_block field in the superblock.
    860  * Programs that check MMP should assume that if SEQ_FSCK (or any unknown
    861  * code above SEQ_MAX) is present then it is NOT safe to use the filesystem,
    862  * regardless of how old the timestamp is.
    863  *
    864  * The timestamp in the MMP structure will be updated by e2fsck at some
    865  * arbitary intervals (start of passes, after every few groups of inodes
    866  * in pass1 and pass1b).  There is no guarantee that e2fsck is updating
    867  * the MMP block in a timely manner, and the updates it does are purely
    868  * for the convenience of the sysadmin and not for automatic validation.
    869  *
    870  * Note: Only the mmp_seq value is used to determine whether the MMP block
    871  *	is being updated.  The mmp_time, mmp_nodename, and mmp_bdevname
    872  *	fields are only for informational purposes for the administrator,
    873  *	due to clock skew between nodes and hostname HA service takeover.
    874  */
    875 #define EXT4_MMP_MAGIC     0x004D4D50U /* ASCII for MMP */
    876 #define EXT4_MMP_SEQ_CLEAN 0xFF4D4D50U /* mmp_seq value for clean unmount */
    877 #define EXT4_MMP_SEQ_FSCK  0xE24D4D50U /* mmp_seq value when being fscked */
    878 #define EXT4_MMP_SEQ_MAX   0xE24D4D4FU /* maximum valid mmp_seq value */
    879 
    880 struct mmp_struct {
    881 	__u32	mmp_magic;		/* Magic number for MMP */
    882 	__u32	mmp_seq;		/* Sequence no. updated periodically */
    883 	__u64	mmp_time;		/* Time last updated */
    884 	char	mmp_nodename[64];	/* Node which last updated MMP block */
    885 	char	mmp_bdevname[32];	/* Bdev which last updated MMP block */
    886 	__u16	mmp_check_interval;	/* Changed mmp_check_interval */
    887 	__u16	mmp_pad1;
    888 	__u32	mmp_pad2[227];
    889 };
    890 
    891 /*
    892  * Default interval for MMP update in seconds.
    893  */
    894 #define EXT4_MMP_UPDATE_INTERVAL	5
    895 
    896 /*
    897  * Maximum interval for MMP update in seconds.
    898  */
    899 #define EXT4_MMP_MAX_UPDATE_INTERVAL	300
    900 
    901 /*
    902  * Minimum interval for MMP checking in seconds.
    903  */
    904 #define EXT4_MMP_MIN_CHECK_INTERVAL     5
    905 
    906 #endif	/* _LINUX_EXT2_FS_H */
    907