Linux0.96c/kernel/blk_drv/blk.h

#ifndef _BLK_H
#define _BLK_H

#define NR_BLK_DEV	10
/*
 * 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

/*
 * 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 {
	int dev;		/* -1 if no request */
	int cmd;		/* READ or WRITE */
	int errors;
	unsigned long sector;
	unsigned long nr_sectors;
	char * buffer;
	struct task_struct * waiting;
	struct buffer_head * bh;
	struct buffer_head * bhtail;
	struct request * next;
};

/*
 * 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) \
((s1)->cmd<(s2)->cmd || ((s1)->cmd==(s2)->cmd && \
((s1)->dev < (s2)->dev || (((s1)->dev == (s2)->dev && \
(s1)->sector < (s2)->sector)))))

struct blk_dev_struct {
	void (*request_fn)(void);
	struct request * current_request;
};

extern struct blk_dev_struct blk_dev[NR_BLK_DEV];
extern struct request request[NR_REQUEST];
extern struct task_struct * wait_for_request;

extern int * blk_size[NR_BLK_DEV];

#ifdef MAJOR_NR

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

#if (MAJOR_NR == 1)
/* ram disk */
#define DEVICE_NAME "ramdisk"
#define DEVICE_REQUEST do_rd_request
#define DEVICE_NR(device) ((device) & 7)
#define DEVICE_ON(device) 
#define DEVICE_OFF(device)

#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)
/* harddisk: timeout is 6 seconds.. */
#define DEVICE_NAME "harddisk"
#define DEVICE_INTR do_hd
#define DEVICE_TIMEOUT HD_TIMER
#define TIMEOUT_VALUE 600
#define DEVICE_REQUEST do_hd_request
#define DEVICE_NR(device) (MINOR(device)>>6)
#define DEVICE_ON(device)
#define DEVICE_OFF(device)

#elif (MAJOR_NR == 8)
/* scsi disk */
#define DEVICE_NAME "scsidisk"
#define DEVICE_INTR do_sd  
#define DEVICE_REQUEST do_sd_request
#define DEVICE_NR(device) (MINOR(device) >> 4)
#define DEVICE_ON(device)
#define DEVICE_OFF(device)

#elif (MAJOR_NR == 9)
/* scsi tape */
#define DEVICE_NAME "scsitape"
#define DEVICE_INTR do_st  
#define DEVICE_REQUEST do_st_request
#define DEVICE_NR(device) (MINOR(device))
#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)
#define CURRENT_DEV DEVICE_NR(CURRENT->dev)

#ifdef DEVICE_INTR
void (*DEVICE_INTR)(void) = NULL;
#endif
#ifdef DEVICE_TIMEOUT

#define SET_TIMER \
((timer_table[DEVICE_TIMEOUT].expires = jiffies + TIMEOUT_VALUE), \
(timer_active |= 1<<DEVICE_TIMEOUT))

#define CLEAR_TIMER \
timer_active &= ~(1<<DEVICE_TIMEOUT)

#define SET_INTR(x) \
if (DEVICE_INTR = (x)) \
	SET_TIMER; \
else \
	CLEAR_TIMER;

#else

#define SET_INTR(x) (DEVICE_INTR = (x))

#endif
static void (DEVICE_REQUEST)(void);

extern inline void unlock_buffer(struct buffer_head * bh)
{
	if (!bh->b_lock)
		printk(DEVICE_NAME ": free buffer being unlocked\n");
	bh->b_lock=0;
	wake_up(&bh->b_wait);
}

static void end_request(int uptodate)
{
	struct request * req;
	struct buffer_head * bh;

	req = CURRENT;
	req->errors = 0;
	if (!uptodate) {
		printk(DEVICE_NAME " I/O error\n\r");
		printk("dev %04x, sector %d\n\r",req->dev,req->sector);
		req->nr_sectors--;
		req->nr_sectors &= ~1;
		req->sector += 2;
		req->sector &= ~1;		
	}
	if (bh = req->bh) {
		req->bh = bh->b_reqnext;
		bh->b_reqnext = NULL;
		bh->b_uptodate = uptodate;
		unlock_buffer(bh);
		if (bh = req->bh) {
			if (req->nr_sectors < 2) {
				req->nr_sectors = 2;
				printk("end_request: buffer-list destroyed\n");
			}
			req->buffer = bh->b_data;
			return;
		}
	}
	DEVICE_OFF(req->dev);
	CURRENT = req->next;
	wake_up(&req->waiting);
	req->dev = -1;
	wake_up(&wait_for_request);
}

#ifdef DEVICE_INTR
#define CLEAR_INTR SET_INTR(NULL)
#else
#define CLEAR_INTR
#endif

#define INIT_REQUEST \
repeat: \
	if (!CURRENT) {\
		CLEAR_INTR; \
		return; \
	} \
	if (MAJOR(CURRENT->dev) != MAJOR_NR) \
		panic(DEVICE_NAME ": request list destroyed"); \
	if (CURRENT->bh) { \
		if (!CURRENT->bh->b_lock) \
			panic(DEVICE_NAME ": block not locked"); \
	}

#endif

#endif