#ifndef _BLK_H#define _BLK_H#define NR_BLK_DEV 7		/*  塊設備的數(shù)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)*//** 下面定義的NR_REQUEST 是請求隊列中所包含的項數(shù)。* 注意，讀操作僅使用這些項低端的2/3；讀操作優(yōu)先處理。** 32 項好象是一個合理的數(shù)字：已經(jīng)足夠從電梯算法中獲得好處，* 但當緩沖區(qū)在隊列中而鎖住時又不顯得是很大的數(shù)。64 就看上* 去太大了（當大量的寫/同步操作運行時很容易引起長時間的暫停）。*/#define NR_REQUEST 32/** 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.*//** OK，下面是request 結構的一個擴展形式，因而當實現(xiàn)以后，我們就可以在分頁請求中* 使用同樣的request 結構。在分頁處理中，'bh'是NULL，而'waiting'則用于等待讀/寫的完成。*/// 下面是請求隊列中項的結構。其中如果dev=-1，則表示該項沒有被使用。struct request{  int dev;						/* -1 if no request */// 使用的設備號。  int cmd;					/* READ or WRITE */// 命令(READ 或WRITE)。  int errors;					/* 操作時產(chǎn)生的錯誤次數(shù)。*/  unsigned long sector;			/* 起始扇區(qū)。(1 塊=2 扇區(qū))*/  unsigned long nr_sectors;		/* 讀/寫扇區(qū)數(shù)。*/  char *buffer;				/* 數(shù)據(jù)緩沖區(qū)。*/  struct task_struct *waiting;	/* 任務等待操作執(zhí)行完成的地方。*/  struct buffer_head *bh;		/* 緩沖區(qū)頭指針(include/linux/fs.h,68)。*/  struct request *next;		/* 指向下一請求項。*/};/** 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.*//** 下面的定義用于電梯算法：注意讀操作總是在寫操作之前進行。* 這是很自然的：讀操作對時間的要求要比寫嚴格得多。*/#define IN_ORDER(s1,s2) \((s1)->cmd<(s2)->cmd || (s1)->cmd==(s2)->cmd && \((s1)->dev < (s2)->dev || ((s1)->dev == (s2)->dev && \(s1)->sector < (s2)->sector)))// 塊設備結構。struct blk_dev_struct{  	void (*request_fn) (void);						/* 請求操作的函數(shù)指針。*/  	struct request *current_request;				/* 請求信息結構。*/};extern struct blk_dev_struct blk_dev[NR_BLK_DEV];	/* 塊設備數(shù)組，每種塊設備占用一項*/extern struct request request[NR_REQUEST];			/* 請求隊列數(shù)組*/extern struct task_struct *wait_for_request;			/* 等待請求的任務結構*/#ifdef MAJOR_NR									/* 主設備號*//** Add entries as needed. Currently the only block devices* supported are hard-disks and floppies.*//** 需要時加入條目。目前塊設備僅支持硬盤和軟盤（還有虛擬盤）。*/#if (MAJOR_NR == 1)								/* RAM 盤的主設備號是1。根據(jù)這里的定義可以推理內(nèi)存塊主設備號也為1 */												/* ram disk *//* RAM 盤（內(nèi)存虛擬盤） */#define DEVICE_NAME "ramdisk"					/* 設備名稱ramdisk */#define DEVICE_REQUEST do_rd_request			/* 設備請求函數(shù)do_rd_request() */#define DEVICE_NR(device) ((device) & 7)			/* 設備號(0--7) */#define DEVICE_ON(device)						/* 開啟設備。虛擬盤無須開啟和關閉*/#define DEVICE_OFF(device)						/* 關閉設備*/#elif (MAJOR_NR == 2)								/* 軟驅的主設備號是2 *//* floppy */#define DEVICE_NAME "floppy"						/* 設備名稱floppy */#define DEVICE_INTR do_floppy						/* 設備中斷處理程序do_floppy() */#define DEVICE_REQUEST do_fd_request			/* 設備請求函數(shù)do_fd_request() */#define DEVICE_NR(device) ((device) & 3)			/* 設備號（0--3） */#define DEVICE_ON(device) floppy_on(DEVICE_NR(device))	/* 開啟設備函數(shù)floppyon() */#define DEVICE_OFF(device) floppy_off(DEVICE_NR(device))	/* 關閉設備函數(shù)floppyoff() */#elif (MAJOR_NR == 3)								/* 硬盤主設備號是3 *//* harddisk */#define DEVICE_NAME "harddisk"					/* 硬盤名稱harddisk */#define DEVICE_INTR do_hd						/* 設備中斷處理程序do_hd() */#define DEVICE_REQUEST do_hd_request			/* 設備請求函數(shù)do_hd_request() */#define DEVICE_NR(device) (MINOR(device)/5)		/* 設備號（0--1）。每個硬盤可以有4 個分區(qū)*/#define DEVICE_ON(device)						/* 硬盤一直在工作，無須開啟和關閉*/#define DEVICE_OFF(device)#elif/* unknown blk device *//* 未知塊設備 */#error "unknown blk device"#endif#define CURRENT (blk_dev[MAJOR_NR].current_request)/* CURRENT 為指定主設備號的當前請求結構*/#define CURRENT_DEV DEVICE_NR(CURRENT->dev)	/* CURRENT_DEV 為CURRENT 的設備號*/#ifdef DEVICE_INTRvoid (*DEVICE_INTR) (void) = NULL;#endifstatic void (DEVICE_REQUEST) (void);// 釋放鎖定的緩沖區(qū)。extern inline void unlock_buffer (struct buffer_head *bh){  	if (!bh->b_lock)								/* 如果指定的緩沖區(qū)bh 并沒有被上鎖，則顯示警告信息*/    		intk (DEVICE_NAME ": free buffer being unlocked\n");	bh->b_lock = 0;								/* 否則將該緩沖區(qū)解鎖*/  	wake_up (&bh->b_wait);						/* 喚醒等待該緩沖區(qū)的進程*/}// 結束請求。extern inline void end_request (int uptodate){	DEVICE_OFF (CURRENT->dev);					/* 關閉設備*/  	if (CURRENT->bh)    	{											/* CURRENT 為指定主設備號的當前請求結構*/      		CURRENT->bh->b_uptodate = uptodate;		/* 置更新標志*/      		unlock_buffer (CURRENT->bh);				/* 解鎖緩沖區(qū)*/    	}	if (!uptodate)    	{											/* 如果更新標志為0 則顯示設備錯誤信息*/      		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);				/* 喚醒等待該請求項的進程*/  	wake_up (&wait_for_request);				/* 喚醒等待請求的進程*/  	CURRENT->dev = -1;							/* 釋放該請求項*/  	CURRENT = CURRENT->next;					/* 從請求鏈表中刪除該請求項*/}// 定義初始化請求宏。#define INIT_REQUEST \repeat: \if (!CURRENT) \									/* 如果當前請求結構指針為null 則返回*/	return;if (MAJOR (CURRENT->dev) != MAJOR_NR)\			/* 如果當前設備的主設備號不對則死機*/    	panic (DEVICE_NAME ": request list destroyed");if (CURRENT->bh){    if (!CURRENT->bh->b_lock) \						/* 如果在進行請求操作時緩沖區(qū)沒鎖定則死機*/	panic (DEVICE_NAME ": block not locked");  }#endif#endif