void buffer_init(long buffer_end)函數的理解：

* 0 0x100000 0x400000 0x10 00000(16M)
* ----------------------------------------------------------
* | kernel | memery buffer | main memory |
* ----------------------------------------------------------

以上圖為例，該段主要初始化memery buffer部分，並且前地址地段儲存緩存頭部，高端儲存緩存塊(1K)；

緩存頭部struct buffer_head

 1 struct buffer_head {
 2     char * b_data;            /* pointer to data block (1024 bytes) */
 3     unsigned long b_blocknr;    /* block number */
 4     unsigned short b_dev;        /* device (0 = free) */
 5     unsigned char
 
 b_uptodate;
 6     unsigned char b_dirt;        /* 0-clean,1-dirty */
 7     unsigned char b_count;        /* users using this block */
 8     unsigned char b_lock;        /* 0 - ok, 1 -locked */
 9     struct task_struct * b_wait;
10     struct buffer_head * b_prev;
11     struct buffer_head * b_next;
12     struct
 
 buffer_head * b_prev_free;
13     struct buffer_head * b_next_free;
14 };

用環形雙鏈表鏈接：

node0 <--->node1<--> ...... <-->noden<-->node0

main.c 流程-buffer初始化