ll_rw_blk.c

arm平台上的uclinux系统全部源代码

/*
 *  linux/drivers/block/ll_rw_blk.c
 *
 * Copyright (C) 1991, 1992 Linus Torvalds
 * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
 */

/*
 * This handles all read/write requests to block devices
 */
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/kernel_stat.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/config.h>
#include <linux/locks.h>
#include <linux/mm.h>

#include <asm/system.h>
#include <asm/io.h>
#include "blk.h"

/*
 * The request-struct contains all necessary data
 * to load a nr of sectors into memory
 */
static struct request all_requests[NR_REQUEST];

/*
 * The "disk" task queue is used to start the actual requests
 * after a plug
 */
DECLARE_TASK_QUEUE(tq_disk);

/*
 * used to wait on when there are no free requests
 */
struct wait_queue * wait_for_request;

/* This specifies how many sectors to read ahead on the disk.  */

int read_ahead[MAX_BLKDEV];

/* blk_dev_struct is:
 *	*request_fn
 *	*current_request
 */
struct blk_dev_struct blk_dev[MAX_BLKDEV]; /* initialized by blk_dev_init() */

/*
 * blk_size contains the size of all block-devices in units of 1024 byte
 * sectors:
 *
 * blk_size[MAJOR][MINOR]
 *
 * if (!blk_size[MAJOR]) then no minor size checking is done.
 */
int * blk_size[MAX_BLKDEV];

/*
 * blksize_size contains the size of all block-devices:
 *
 * blksize_size[MAJOR][MINOR]
 *
 * if (!blksize_size[MAJOR]) then 1024 bytes is assumed.
 */
int * blksize_size[MAX_BLKDEV];

/*
 * hardsect_size contains the size of the hardware sector of a device.
 *
 * hardsect_size[MAJOR][MINOR]
 *
 * if (!hardsect_size[MAJOR])
 *		then 512 bytes is assumed.
 * else
 *		sector_size is hardsect_size[MAJOR][MINOR]
 * This is currently set by some scsi device and read by the msdos fs driver
 * This might be a some uses later.
 */
int * hardsect_size[MAX_BLKDEV];

/*
 * remove the plug and let it rip..
 */
void unplug_device(void * data)
{
	struct blk_dev_struct * dev = (struct blk_dev_struct *) data;
	unsigned long flags;

	save_flags_cli(flags);
	if (dev->current_request == &dev->plug) {
		struct request * next = dev->plug.next;
		dev->current_request = next;
		if (next) {
			dev->plug.next = NULL;
			(dev->request_fn)();
		}
	}
	restore_flags(flags);
}

/*
 * "plug" the device if there are no outstanding requests: this will
 * force the transfer to start only after we have put all the requests
 * on the list.
 *
 * This is called with interrupts off and no requests on the queue.
 */
static inline void plug_device(struct blk_dev_struct * dev)
{
	dev->current_request = &dev->plug;
	queue_task_irq_off(&dev->plug_tq, &tq_disk);
}

/*
 * look for a free request in the first N entries.
 * NOTE: interrupts must be disabled on the way in, and will still
 *       be disabled on the way out.
 */
static inline struct request * get_request(int n, kdev_t dev)
{
	static struct request *prev_found = NULL, *prev_limit = NULL;
	register struct request *req, *limit;

	if (n <= 0)
		panic("get_request(%d): impossible!\n", n);

	limit = all_requests + n;
	if (limit != prev_limit) {
		prev_limit = limit;
		prev_found = all_requests;
	}
	req = prev_found;
	for (;;) {
		req = ((req > all_requests) ? req : limit) - 1;
		if (req->rq_status == RQ_INACTIVE)
			break;
		if (req == prev_found)
			return NULL;
	}
	prev_found = req;
	req->rq_status = RQ_ACTIVE;
	req->rq_dev = dev;
	return req;
}

/*
 * wait until a free request in the first N entries is available.
 */
static struct request * __get_request_wait(int n, kdev_t dev)
{
	register struct request *req;
	struct wait_queue wait = { current, NULL };

	add_wait_queue(&wait_for_request, &wait);
	for (;;) {
		current->state = TASK_UNINTERRUPTIBLE;
		cli();
		req = get_request(n, dev);
		sti();
		if (req)
			break;
		run_task_queue(&tq_disk);
		schedule();
	}
	remove_wait_queue(&wait_for_request, &wait);
	current->state = TASK_RUNNING;
	return req;
}

static inline struct request * get_request_wait(int n, kdev_t dev)
{
	register struct request *req;

	cli();
	req = get_request(n, dev);
	sti();
	if (req)
		return req;
	return __get_request_wait(n, dev);
}

/* RO fail safe mechanism */

static long ro_bits[MAX_BLKDEV][8];

int is_read_only(kdev_t dev)
{
	int minor,major;

	major = MAJOR(dev);
	minor = MINOR(dev);
	if (major < 0 || major >= MAX_BLKDEV) return 0;
	return ro_bits[major][minor >> 5] & (1 << (minor & 31));
}

void set_device_ro(kdev_t dev,int flag)
{
	int minor,major;

	major = MAJOR(dev);
	minor = MINOR(dev);
	if (major < 0 || major >= MAX_BLKDEV) return;
	if (flag) ro_bits[major][minor >> 5] |= 1 << (minor & 31);
	else ro_bits[major][minor >> 5] &= ~(1 << (minor & 31));
}

static inline void drive_stat_acct(int cmd, unsigned long nr_sectors,
                                   short disk_index)
{
	kstat.dk_drive[disk_index]++;
	if (cmd == READ) {
		kstat.dk_drive_rio[disk_index]++;
		kstat.dk_drive_rblk[disk_index] += nr_sectors;
	} else if (cmd == WRITE) {
		kstat.dk_drive_wio[disk_index]++;
		kstat.dk_drive_wblk[disk_index] += nr_sectors;
	} else
		printk(KERN_ERR "drive_stat_acct: cmd not R/W?\n");
}

/*
 * add-request adds a request to the linked list.
 * It disables interrupts so that it can muck with the
 * request-lists in peace.
 *
 * By this point, req->cmd is always either READ/WRITE, never READA/WRITEA,
 * which is important for drive_stat_acct() above.
 */

void add_request(struct blk_dev_struct * dev, struct request * req)
{
	struct request * tmp;
	short		 disk_index;

	switch (MAJOR(req->rq_dev)) {
		case SCSI_DISK_MAJOR:
			disk_index = (MINOR(req->rq_dev) & 0x0070) >> 4;
			if (disk_index < 4)
				drive_stat_acct(req->cmd, req->nr_sectors, disk_index);
			break;
		case IDE0_MAJOR:	/* same as HD_MAJOR */
		case XT_DISK_MAJOR:
			disk_index = (MINOR(req->rq_dev) & 0x0040) >> 6;
			drive_stat_acct(req->cmd, req->nr_sectors, disk_index);
			break;
		case IDE1_MAJOR:
			disk_index = ((MINOR(req->rq_dev) & 0x0040) >> 6) + 2;
			drive_stat_acct(req->cmd, req->nr_sectors, disk_index);
		default:
			break;
	}

	req->next = NULL;
	cli();
	if (req->bh)
		mark_buffer_clean(req->bh);
	if (!(tmp = dev->current_request)) {
		dev->current_request = req;
		(dev->request_fn)();
		sti();
		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;

/* for SCSI devices, call request_fn unconditionally */
	if (scsi_blk_major(MAJOR(req->rq_dev)))
		(dev->request_fn)();

	sti();
}

#define MAX_SECTORS 244

static inline void attempt_merge (struct request *req)
{
	struct request *next = req->next;

	if (!next)
		return;
	if (req->sector + req->nr_sectors != next->sector)
		return;
	if (next->sem || req->cmd != next->cmd || req->rq_dev != next->rq_dev || req->nr_sectors + next->nr_sectors >= MAX_SECTORS)
		return;
#if 0
	printk ("%s: merge %ld, %ld + %ld == %ld\n", kdevname(req->rq_dev), req->sector, req->nr_sectors, next->nr_sectors, req->nr_sectors + next->nr_sectors);
#endif
	req->bhtail->b_reqnext = next->bh;
	req->bhtail = next->bhtail;
	req->nr_sectors += next->nr_sectors;
	next->rq_status = RQ_INACTIVE;
	req->next = next->next;
	wake_up (&wait_for_request);
}

void make_request(int major,int rw, struct buffer_head * bh)
{
	unsigned int sector, count;
	struct request * req;
	int rw_ahead, max_req;

	count = bh->b_size >> 9;
	sector = bh->b_rsector;

	/* Uhhuh.. Nasty dead-lock possible here.. */
	if (buffer_locked(bh)) {
#if 0
		printk("make_request(): buffer already locked\n");
#endif
		return;
	}
	/* Maybe the above fixes it, and maybe it doesn't boot. Life is interesting */

	lock_buffer(bh);

	if (blk_size[major])
		if (blk_size[major][MINOR(bh->b_rdev)] < (sector + count)>>1) {
			bh->b_state &= (1 << BH_Lock) | (1 << BH_FreeOnIO);
                        /* This may well happen - the kernel calls bread()
                           without checking the size of the device, e.g.,
                           when mounting a device. */
			printk(KERN_INFO
                               "attempt to access beyond end of device\n");
			printk(KERN_INFO "%s: rw=%d, want=%d, limit=%d\n",
                               kdevname(bh->b_rdev), rw,
                               (sector + count)>>1,
                               blk_size[major][MINOR(bh->b_rdev)]);
			unlock_buffer(bh);
			return;
		}

	rw_ahead = 0;	/* normal case; gets changed below for READA/WRITEA */
	switch (rw) {
		case READA:
			rw_ahead = 1;
			rw = READ;	/* drop into READ */
		case READ:
			if (buffer_uptodate(bh)) {
#if 0
				printk ("make_request(): buffer uptodate for READ\n");
#endif