blk.h.bak

一份精简的linux内核源代码

#ifndef _BLK_H
#define _BLK_H

#define NR_BLK_DEV	7/*块设备数量*/
/*
 * NR_REQUEST is the number of entries in the request-queue.
 * NOTE that writes may use only the low 2/3 of these: reads
 * take precedence.
 *
 * 32 seems to be a reasonable number: enough to get some benefit
 * from the elevator-mechanism, but not so much as to lock a lot of
 * buffers when they are in the queue. 64 seems to be too many (easily
 * long pauses in reading when heavy writing/syncing is going on)
 */
#define NR_REQUEST	32/*块设备请求项数*/

/*
 * Ok, this is an expanded form so that we can use the same
 * request for paging requests when that is implemented. In
 * paging, 'bh' is NULL, and 'waiting' is used to wait for
 * read/write completion.
 */
struct request {/*请求项*/
	int dev;		/* -1 if no request *//*设备号*/
	int cmd;		/* READ or WRITE */
	int errors;     /*操作时的出错数*/
	unsigned long sector;/*起始扇区*/
	unsigned long nr_sectors;/*读写扇区数*/
	char * buffer;    /*读写缓冲区*/
	struct task_struct * waiting;
	struct buffer_head * bh;/*缓冲区头指针*/
	struct request * next;/*下一个请求项*/
};

/*
 * This is used in the elevator algorithm: Note that
 * reads always go before writes. This is natural: reads
 * are much more time-critical than writes.
 */
#define IN_ORDER(s1,s2) \ /*判断两个请求项的顺序*/
((s1)->cmd<(s2)->cmd || (s1)->cmd==(s2)->cmd && \
((s1)->dev < (s2)->dev || ((s1)->dev == (s2)->dev && \
(s1)->sector < (s2)->sector)))

struct blk_dev_struct {/*块设备表*/
	void (*request_fn)(void);/*该块设备的相应处理程序*/
	struct request * current_request;/*该块设备当前正在处理的请求*/
};

extern struct blk_dev_struct blk_dev[NR_BLK_DEV];/*块设备表数组*/
extern struct request request[NR_REQUEST];/*请求项队列数组*/
extern struct task_struct * wait_for_request;/*等待空闲请求项的进程队列头指针*/

#ifdef MAJOR_NR/*主设备号*/

/*
 * Add entries as needed. Currently the only block devices
 * supported are hard-disks and floppies.
 */

#if (MAJOR_NR == 1)/*是内存*/
/* ram disk */
#define DEVICE_NAME "ramdisk"
#define DEVICE_REQUEST do_rd_request
#define DEVICE_NR(device) ((device) & 7)/*设备号*/
#define DEVICE_ON(device) /*开启设备*/
#define DEVICE_OFF(device)/*关闭设备*/

#elif (MAJOR_NR == 2)
/* floppy */
#define DEVICE_NAME "floppy"
#define DEVICE_INTR do_floppy
#define DEVICE_REQUEST do_fd_request
#define DEVICE_NR(device) ((device) & 3)
#define DEVICE_ON(device) floppy_on(DEVICE_NR(device))
#define DEVICE_OFF(device) floppy_off(DEVICE_NR(device))

#elif (MAJOR_NR == 3)/*是硬盘*/
/* harddisk */
#define DEVICE_NAME "harddisk"
#define DEVICE_INTR do_hd
#define DEVICE_REQUEST do_hd_request
#define DEVICE_NR(device) (MINOR(device)/5)/*每个硬盘可有4个分区*/
#define DEVICE_ON(device)
#define DEVICE_OFF(device)

#elif
/* unknown blk device */
#error "unknown blk device"

#endif

#define CURRENT (blk_dev[MAJOR_NR].current_request)/*指定主设备号的当前请求项指针*/
#define CURRENT_DEV DEVICE_NR(CURRENT->dev)/*当前请求项中的设备*/

#ifdef DEVICE_INTR
void (*DEVICE_INTR)(void) = NULL;
#endif
static void (DEVICE_REQUEST)(void);

extern inline void unlock_buffer(struct buffer_head * bh)/*解锁缓冲区，并唤醒等待该缓冲区的进程*/
{
	if (!bh->b_lock)
		printk(DEVICE_NAME ": free buffer being unlocked\n");
	bh->b_lock=0;
	wake_up(&bh->b_wait);
}

extern inline void end_request(int uptodate)/*结束请求处理*/
{
	DEVICE_OFF(CURRENT->dev);/*关闭设备*/
	if (CURRENT->bh) {
		CURRENT->bh->b_uptodate = uptodate;
		unlock_buffer(CURRENT->bh);
	}
	if (!uptodate) {
		printk(DEVICE_NAME " I/O error\n\r");
		printk("dev %04x, block %d\n\r",CURRENT->dev,
			CURRENT->bh->b_blocknr);
	}
	wake_up(&CURRENT->waiting);/*唤醒等待该请求项的进程*/
	wake_up(&wait_for_request);/*唤醒等待空闲请求项的进程*/
	CURRENT->dev = -1;/*释放该请求项*/
	CURRENT = CURRENT->next;/*当前请求项指针指向下一个请求项*/
}

#define INIT_REQUEST \ /*初始化请求项*/
repeat: \
	if (!CURRENT) \ /*无需要处理的请求项*/
		return; \
	if (MAJOR(CURRENT->dev) != MAJOR_NR) \ /*出错*/
		panic(DEVICE_NAME ": request list destroyed"); \
	if (CURRENT->bh) { \ /*出错*/
		if (!CURRENT->bh->b_lock) \
			panic(DEVICE_NAME ": block not locked"); \
	}

#endif

#endif