ext2_last_byte
limit = kaddr + ext2_last_byte(inode, n) - EXT2_DIR_REC_LEN(1);
kaddr += ext2_last_byte(dir, n) - reclen;
dir_end = kaddr + ext2_last_byte(dir, n);
kaddr += ext2_last_byte(inode, i) - EXT2_DIR_REC_LEN(1);