12.块设备驱动程序（磁盘）

1.小结

1. 分配gendisk结构
2. 分配设置队列，队列提供实际的读写函数，这个会赋值到gendisk
3. 注册块设备驱动（对比注册字符设备驱动，并没有提供一个file_operations）
4. 设置gendisk参数，包括先前的队列
5. 注册这个gendisk

2.关键函数解析

• register_blkdev
  注册块设备

  int register_blkdev(unsigned int major, const char *name) //如果major为0则为其自动分配主设备号

• gendisk
  磁盘设备

  struct gendisk {
  int major; /* major number of driver /
  int first_minor;
  int minors; / maximum number of minors, =1 for
  * disks that can't be partitioned. 分区此设备数，在alloc_disk中分配/
  char disk_name[DISK_NAME_LEN]; / name of major driver */
  char (devnode)(struct gendisk *gd, umode_t *mode);

  unsigned int events; /* supported events /
  unsigned int async_events; / async events, subset of all */

  /* Array of pointers to partitions indexed by partno.
  * Protected with matching bdev lock but stat and other
  * non-critical accesses use RCU. Always access through
  * helpers.
  */
  struct disk_part_tbl __rcu *part_tbl;
  struct hd_struct part0; //分区表信息

  const struct block_device_operations *fops; //块设备的操作函数
  struct request_queue *queue; //请求队列，用于管理设备IO请求队列的指针
  void *private_data; //私有数据

  int flags;
  struct device *driverfs_dev; // FIXME: remove
  struct kobject *slave_dir;

  struct timer_rand_state random;
  atomic_t sync_io; / RAID */
  struct disk_events *ev;
  #ifdef CONFIG_BLK_DEV_INTEGRITY
  struct blk_integrity *integrity;
  #endif
  int node_id;
  };

• void set_capacity(struct gendisk *disk, sector_t size)
  设置扇区数。512位一个扇区，描述设备容量

  static inline void set_capacity(struct gendisk *disk, sector_t size)
  {
  disk->part0.nr_sects = size;
  }

3.代码解析

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)
{
/ 容量=headscylinderssectors512 */
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)
{
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) { //电梯算法
/* 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)
{
//printk("do_ramblock_request read %d\n", ++r_cnt);
memcpy(req->buffer, ramblock_buf+offset, len);
}
else
{
//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); //do_ramblock_request具体的读写函数
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); //kzalloc申请内存外还会清零

/* 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");