块设备驱动程序

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框架：

app: open,read,write "1.txt"
--------------------------------------------- 文件的读写
文件系统: vfat, ext2, ext3, yaffs2, jffs2 (把文件的读写转换为扇区的读写)
-----------------ll_rw_block----------------- 扇区的读写
1. 把"读写"放入队列
2. 调用队列的处理函数(优化/调顺序/合并)
块设备驱动程序
---------------------------------------------
硬件: 硬盘,flash

<LINUX内核源代码情景分析>

分析ll_rw_block
for (i = 0; i < nr; i++) {
struct buffer_head *bh = bhs[i];
submit_bh(rw, bh);
struct bio *bio; // 使用bh来构造bio (block input/output)
submit_bio(rw, bio);
// 通用的构造请求: 使用bio来构造请求(request)
generic_make_request(bio);
__generic_make_request(bio);
request_queue_t *q = bdev_get_queue(bio->bi_bdev); // 找到队列

// 调用队列的"构造请求函数"
ret = q->make_request_fn(q, bio); //搜索make_request_fn 找到 q->make_request_fn = mfn;
// 默认的函数是__make_request
__make_request
// 先尝试合并；elevator ：电梯
elv_merge(q, &req, bio);

// 如果合并不成，使用bio构造请求
init_request_from_bio(req, bio);

// 把请求放入队列
add_request(q, req);

// 执行队列
__generic_unplug_device(q);
// 调用队列的"处理函数"
q->request_fn(q);

怎么写块设备驱动程序呢？
1. 分配gendisk: alloc_disk
2. 设置
2.1 分配/设置队列: request_queue_t // 它提供读写能力
blk_init_queue
2.2 设置gendisk其他信息 // 它提供属性: 比如容量
3. 注册: add_disk

参考：
drivers\block\xd.c
drivers\block\z2ram.c

（分配一块内存，在这个内存里模拟硬盘）
测试3th,4th:
在开发板上:
1. insmod ramblock.ko
2. 格式化: mkdosfs /dev/ramblock
3. 挂接: mount /dev/ramblock /tmp/
4. 读写文件: cd /tmp, 在里面vi文件
5. cd /; umount /tmp/
6. cat /dev/ramblock > /mnt/ramblock.bin   (把 /dev/ramblock拷贝到 /mnt/ramblock.bin文件里)
7. 在PC上查看ramblock.bin
sudo mount -o loop ramblock.bin /mnt ( -o loop 可以把普通文件当做块设备挂接)

测试5th:
1. insmod ramblock.ko
2. ls /dev/ramblock*

3. fdisk /dev/ramblock （fdisk 对硬盘进行分区）

# fdisk /dev/ramblock （分区）
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that the previous content
won't be recoverable.

Warning: invalid flag 0x00,0x00 of partition table 4 will be corrected by w(rite)

Command (m for help): m
Command Action
a toggle a bootable flag
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition
l list known partition types
n add a new partition
o create a new empty DOS partition table
p print the partition table
q quit without saving changes
s create a new empty Sun disklabel
t change a partition's system id
u change display/entry units
v verify the partition table
w write table to disk and exit （分区后，最后一步要把分区表写进磁盘，并退出。也就是保存分区）
x extra functionality (experts only)

Command (m for help): n
Command action
e extended （扩展分区）
p primary partition (1-4) （主分区）
p
Partition number (1-4): 1 //第一个主分区
First cylinder (1-32, default 1): 1 //第一个柱面
Last cylinder or +size or +sizeM or +sizeK (6-32, default 32): 10 //第10个柱面

-----------------------------------------------------------------------------------------------------------------------------

//用内存来模拟块设备驱动程序

/* 参考:
* drivers\block\xd.c
* drivers\block\z2ram.c
*/

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/genhd.h>
#include <linux/hdreg.h>
#include <linux/ioport.h>
#include <linux/init.h>
#include <linux/wait.h>
#include <linux/blkdev.h>
#include <linux/blkpg.h>
#include <linux/delay.h>
#include <linux/io.h>

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/dma.h>

static struct gendisk *ramblock_disk;
static request_queue_t *ramblock_queue;

static int major;

static DEFINE_SPINLOCK(ramblock_lock);

#define RAMBLOCK_SIZE (1024*1024)
static unsigned char *ramblock_buf;

static int ramblock_getgeo(struct block_device *bdev, struct hd_geometry *geo)
{ //磁头、柱面、扇区
/* 容量=heads*cylinders*sectors*512 */
geo->heads = 2;
geo->cylinders = 32;
geo->sectors = RAMBLOCK_SIZE/2/32/512;
return 0;
}

static struct block_device_operations ramblock_fops = {
.owner = THIS_MODULE,
.getgeo = ramblock_getgeo,
};

static void do_ramblock_request(request_queue_t * q) //处理队列的函数
{ // 它提供读写能力
static int r_cnt = 0;
static int w_cnt = 0;
struct request *req;

//printk("do_ramblock_request %d\n", ++cnt);

while ((req = elv_next_request(q)) != NULL) { //以电梯调度算法取出下一个请求
/* 数据传输三要素: 源,目的,长度 */
/* 源/目的: */
unsigned long offset = req->sector * 512;

/* 目的/源: */
// req->buffer

/* 长度: */
unsigned long len = req->current_nr_sectors * 512;

if (rq_data_dir(req) == READ)
{//从磁盘里读数据，读到req->buffer里
//printk("do_ramblock_request read %d\n", ++r_cnt);
memcpy(req->buffer, ramblock_buf+offset, len);
}//ramblock_buf+offset 起始地址加上偏移值
else
{//向磁盘里写数据
//printk("do_ramblock_request write %d\n", ++w_cnt);
memcpy(ramblock_buf+offset, req->buffer, len);
}

end_request(req, 1);
}
}

static int ramblock_init(void)
{
/* 1. 分配一个gendisk结构体 */
ramblock_disk = alloc_disk(16); /* 次设备号个数: 分区个数+1 */

/* 2. 设置 */
/* 2.1 分配/设置队列: 提供读写能力 */
ramblock_queue = blk_init_queue(do_ramblock_request, &ramblock_lock);
ramblock_disk->queue = ramblock_queue;

/* 2.2 设置其他属性: 比如容量 */
major = register_blkdev(0, "ramblock"); /* cat /proc/devices */
ramblock_disk->major = major;
ramblock_disk->first_minor = 0;
sprintf(ramblock_disk->disk_name, "ramblock");
ramblock_disk->fops = &ramblock_fops;
set_capacity(ramblock_disk, RAMBLOCK_SIZE / 512);

/* 3. 硬件相关操作 */
ramblock_buf = kzalloc(RAMBLOCK_SIZE, GFP_KERNEL); //分配一块内存

/* 4. 注册 */
add_disk(ramblock_disk);

return 0;
}

static void ramblock_exit(void)
{
unregister_blkdev(major, "ramblock");
del_gendisk(ramblock_disk);
put_disk(ramblock_disk);
blk_cleanup_queue(ramblock_queue);

kfree(ramblock_buf);
}

module_init(ramblock_init);
module_exit(ramblock_exit);

MODULE_LICENSE("GPL");

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