flst_node_t中存有12个字节的内容，前6个字节（page:4 boffset:2）表示相对自己前一个node的fil_addr_t信息，后6个字节表示相对自己后1个node的fil_addr_t。除了flst_node_t以外，磁盘链表还有一个头信息
flst_base_node_t，头信息是一个节点个数FLST_LEN（4字节） + FLST_FIRST (6字节)+ FLST_LAST（6字节）
/********************************************************************//**
Gets list last node address.
@return file address */
UNIV_INLINE
fil_addr_t
flst_get_last(
/*==========*/
const flst_base_node_t* base, /*!< in: pointer to base node */
mtr_t* mtr) /*!< in: mini-transaction handle */
{
return(flst_read_addr(base + FLST_LAST, mtr));
}
/********************************************************************//**
Reads a file address.
@return file address */
UNIV_INLINE
fil_addr_t
flst_read_addr(
/*===========*/
const fil_faddr_t* faddr, /*!< in: pointer to file faddress */
mtr_t* mtr) /*!< in: mini-transaction handle */
{
fil_addr_t addr;
ut_ad(faddr && mtr);
addr.page = mtr_read_ulint(faddr + FIL_ADDR_PAGE, MLOG_4BYTES, mtr);
addr.boffset = mtr_read_ulint(faddr + FIL_ADDR_BYTE, MLOG_2BYTES,
mtr);
ut_a(addr.page == FIL_NULL || addr.boffset >= FIL_PAGE_DATA);
ut_a(ut_align_offset(faddr, UNIV_PAGE_SIZE) >= FIL_PAGE_DATA);
return(addr);
}
#define FIL_ADDR_PAGE 0 /* first in address is the page offset */
#define FIL_ADDR_BYTE 4 /* then comes 2-byte byte offset within page*/