/* *  linux/kernel/blk_dev/ll_rw.c * * (C) 1991 Linus Torvalds *//* * This handles all read/write requests to block devices */#include <errno.h>#include <linux/sched.h>#include <linux/kernel.h>#include <asm/system.h>#include "blk.h"/* * The request-struct contains all necessary data * to load a nr of sectors into memory */struct request request[NR_REQUEST];/* * used to wait on when there are no free requests */struct task_struct * wait_for_request = NULL;/* blk_dev_struct is: *	do_request-address *	next-request */struct blk_dev_struct blk_dev[NR_BLK_DEV] = {	{ NULL, NULL },		/* no_dev */	{ NULL, NULL },		/* dev mem */	{ NULL, NULL },		/* dev fd */	{ NULL, NULL },		/* dev hd */	{ NULL, NULL },		/* dev ttyx */	{ NULL, NULL },		/* dev tty */	{ NULL, NULL }		/* dev lp */};static inline void lock_buffer(struct buffer_head * bh){	cli();	while (bh->b_lock)		sleep_on(&bh->b_wait);	bh->b_lock=1;	sti();}static inline void unlock_buffer(struct buffer_head * bh){	if (!bh->b_lock)		printk("ll_rw_block.c: buffer not locked\n\r");	bh->b_lock = 0;	wake_up(&bh->b_wait);}/* * add-request adds a request to the linked list. * It disables interrupts so that it can muck with the * request-lists in peace. */static void add_request(struct blk_dev_struct * dev, struct request * req){	struct request * tmp;	req->next = NULL;	cli();	if (req->bh)		req->bh->b_dirt = 0;	if (!(tmp = dev->current_request)) {		dev->current_request = req;		sti();		(dev->request_fn)();		return;	}	for ( ; tmp->next ; tmp=tmp->next)		if ((IN_ORDER(tmp,req) ||		    !IN_ORDER(tmp,tmp->next)) &&		    IN_ORDER(req,tmp->next))			break;	req->next=tmp->next;	tmp->next=req;	sti();}static void make_request(int major,int rw, struct buffer_head * bh){	struct request * req;	int rw_ahead;/* WRITEA/READA is special case - it is not really needed, so if the *//* buffer is locked, we just forget about it, else it's a normal read */	if (rw_ahead = (rw == READA || rw == WRITEA)) {		if (bh->b_lock)			return;		if (rw == READA)			rw = READ;		else			rw = WRITE;	}	if (rw!=READ && rw!=WRITE)		panic("Bad block dev command, must be R/W/RA/WA");	lock_buffer(bh);	if ((rw == WRITE && !bh->b_dirt) || (rw == READ && bh->b_uptodate)) {		unlock_buffer(bh);		return;	}repeat:/* we don't allow the write-requests to fill up the queue completely: * we want some room for reads: they take precedence. The last third * of the requests are only for reads. */	if (rw == READ)		req = request+NR_REQUEST;	else		req = request+((NR_REQUEST*2)/3);/* find an empty request */	while (--req >= request)		if (req->dev<0)			break;/* if none found, sleep on new requests: check for rw_ahead */	if (req < request) {		if (rw_ahead) {			unlock_buffer(bh);			return;		}		sleep_on(&wait_for_request);		goto repeat;	}/* fill up the request-info, and add it to the queue */	req->dev = bh->b_dev;	req->cmd = rw;	req->errors=0;	req->sector = bh->b_blocknr<<1;	req->nr_sectors = 2;	req->buffer = bh->b_data;	req->waiting = NULL;	req->bh = bh;	req->next = NULL;	add_request(major+blk_dev,req);}void ll_rw_block(int rw, struct buffer_head * bh){	unsigned int major;	if ((major=MAJOR(bh->b_dev)) >= NR_BLK_DEV ||	!(blk_dev[major].request_fn)) {		printk("Trying to read nonexistent block-device\n\r");		return;	}	make_request(major,rw,bh);}void blk_dev_init(void){	int i;	for (i=0 ; i<NR_REQUEST ; i++) {		request[i].dev = -1;		request[i].next = NULL;	}}