struct ext4_inode {
 __le16 i_mode;  /* File mode */
 __le16 i_uid;  /* Low 16 bits of Owner Uid */
 __le32 i_size_lo; /* Size in bytes */
 __le32 i_atime; /* Access time */
 __le32 i_ctime; /* Inode Change time */
 __le32 i_mtime; /* Modification time */
 __le32 i_dtime; /* Deletion Time */
 __le16 i_gid;  /* Low 16 bits of Group Id */
 __le16 i_links_count; /* Links count */
 __le32 i_blocks_lo; /* Blocks count */
 __le32 i_flags; /* File flags */
 union {
  struct {
   __le32 l_i_version;
  } linux1;
  struct {
   __u32 h_i_translator;
  } hurd1;
  struct {
   __u32 m_i_reserved1;
  } masix1;
 } osd1;    /* OS dependent 1 */
 __le32 i_block[EXT4_N_BLOCKS];/* Pointers to blocks */
 __le32 i_generation; /* File version (for NFS) */
 __le32 i_file_acl_lo; /* File ACL */
 __le32 i_size_high;
 __le32 i_obso_faddr; /* Obsoleted fragment address */
 union {
  struct {
   __le16 l_i_blocks_high; /* were l_i_reserved1 */
   __le16 l_i_file_acl_high;
   __le16 l_i_uid_high; /* these 2 fields */
   __le16 l_i_gid_high; /* were reserved2[0] */
   __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 */
   __u16 h_i_mode_high;
   __u16 h_i_uid_high;
   __u16 h_i_gid_high;
   __u32 h_i_author;
  } hurd2;
  struct {
   __le16 h_i_reserved1; /* Obsoleted fragment number/size which are removed in ext4 */
   __le16 m_i_file_acl_high;
   __u32 m_i_reserved2[2];
  } masix2;
 } osd2;    /* OS dependent 2 */
 __le16 i_extra_isize;
 __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) */
 __le32 i_crtime; /* File Creation time */
 __le32 i_crtime_extra; /* extra FileCreationtime (nsec << 2 | epoch) */
 __le32 i_version_hi; /* high 32 bits for 64-bit version */
 __le32 i_projid; /* Project ID */
};

#define EXT4_NDIR_BLOCKS 12
#define EXT4_IND_BLOCK EXT4_NDIR_BLOCKS
#define EXT4_DIND_BLOCK (EXT4_IND_BLOCK + 1)
#define EXT4_TIND_BLOCK (EXT4_DIND_BLOCK + 1)
#define EXT4_N_BLOCKS (EXT4_TIND_BLOCK + 1)

struct ext4_extent_header {
 __le16 eh_magic; /* ext4 extents标识：0xF30A */
 __le16 eh_entries; /* 当前层级中有效节点的数目 */
 __le16 eh_max; /* 当前层级中最大节点的数目 */
 __le16 eh_depth; /* 当前层级在树中的深度，0为叶子节点，即数据节点，>0代表索引节点 */
 __le32 eh_generation; 
}
struct ext4_extent {
 __le32 ee_block; /* extent的起始block逻辑序号 */
 __le16 ee_len; /* extent包含的block个数 */
 __le16 ee_start_hi; /*extent起始block的物理地址的高16位 */
 __le32 ee_start_lo; /*extent起始block的物理地址的低32位 */
};//数据节点中的extent_body格式
struct ext4_extent_idx {
 __le32 ei_block; /* 索引所覆盖的文件范围的起始block的逻辑序号 */
 __le32 ei_leaf_lo; /* 存放下一级extents的block的物理地址的低32位 */ 
 __le16 ei_leaf_hi; /* 存放下一级extents的block的物理地址的高16位 */
 __u16 ei_unused;

};//索引节点中的extent_body格式