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本例中相关的代码为：
BLK_INIT_QUEUE(BLK_DEFAULT_QUEUE(MAJOR_NR), &mtdblock_request, &mtdblock_lock);
blk_cleanup_queue(BLK_DEFAULT_QUEUE(MAJOR_NR)); |
每个设备有一个默认使用的请求队列，必要时，可使用 BLK_DEFAULT_QUEUE(major) 宏得到该默认队列。这个宏在 blk_dev_struct 结构形成的全局数组（该数组名为 blk_dev）中搜索得到对应的默认队列。blk_dev 数组由内核维护，并可通过主设备号索引。blk_dev_struct 接口定义如下：
struct blk_dev_struct {
/*
* queue_proc has to be atomic
*/
request_queue_t request_queue;
queue_proc *queue;
void *data;
}; |
request_queue 成员包含了初始化之后的 I/O 请求队列，data 成员可由驱动程序使用，以便保存一些私有数据。
request_queue定义为：
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struct request_queue
{
/*
* the queue request freelist, one for reads and one for writes
*/
struct request_list rq[2];
/*
* Together with queue_head for cacheline sharing
*/
struct list_head queue_head;
elevator_t elevator;
request_fn_proc * request_fn;
merge_request_fn * back_merge_fn;
merge_request_fn * front_merge_fn;
merge_requests_fn * merge_requests_fn;
make_request_fn * make_request_fn;
plug_device_fn * plug_device_fn;
/*
* The queue owner gets to use this for whatever they like.
* ll_rw_blk doesn't touch it.
*/
void * queuedata;
/*
* This is used to remove the plug when tq_disk runs.
*/
struct tq_struct plug_tq;
/*
* Boolean that indicates whether this queue is plugged or not.
*/
char plugged;
/*
* Boolean that indicates whether current_request is active or
* not.
*/
char head_active;
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