@pynix 对的

#define EXT4_GOOD_OLD_INODE_SIZE 128
...
#define EXT4_GOOD_OLD_REV 0 /* The good old (original) format */
...
/* s 一般是 super_block */
#define EXT4_INODE_SIZE(s) (((s)->s_rev_level == EXT4_GOOD_OLD_REV) ? \
EXT4_GOOD_OLD_INODE_SIZE : \
(s)->s_inode_size)


/*s_inode_size ：
sbi 是 ext4_sb_info ， sb=superblock
*/

if (le32_to_cpu(es->s_rev_level) == EXT4_GOOD_OLD_REV) {
sbi->s_inode_size = EXT4_GOOD_OLD_INODE_SIZE;
sbi->s_first_ino = EXT4_GOOD_OLD_FIRST_INO;
} else {
sbi->s_inode_size = le16_to_cpu(es->s_inode_size);
sbi->s_first_ino = le32_to_cpu(es->s_first_ino);
...