drivers/mtd/mtd_blkdevs.c - arm/linux - Git at Google

 /*
  * $Id: mtd_blkdevs.c,v 1.27 2005/11/07 11:14:20 gleixner Exp $
  *
  * (C) 2003 David Woodhouse <dwmw2@infradead.org>
  *
  * Interface to Linux 2.5 block layer for MTD 'translation layers'.
  *
  */

 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/list.h>
 #include <linux/fs.h>
 #include <linux/mtd/blktrans.h>
 #include <linux/mtd/mtd.h>
 #include <linux/blkdev.h>
 #include <linux/blkpg.h>
 #include <linux/spinlock.h>
 #include <linux/hdreg.h>
 #include <linux/init.h>
 #include <asm/semaphore.h>
 #include <asm/uaccess.h>

 static LIST_HEAD(blktrans_majors);

 extern struct semaphore mtd_table_mutex;
 extern struct mtd_info *mtd_table[];

 struct mtd_blkcore_priv {
 	struct completion thread_dead;
 	int exiting;
 	wait_queue_head_t thread_wq;
 	struct request_queue *rq;
 	spinlock_t queue_lock;
 };

 static int do_blktrans_request(struct mtd_blktrans_ops *tr,
 			       struct mtd_blktrans_dev *dev,
 			       struct request *req)
 {
 	unsigned long block, nsect;
 	char *buf;

 	block = req->sector;
 	nsect = req->current_nr_sectors;
 	buf = req->buffer;

 	if (!(req->flags & REQ_CMD))
 		return 0;

 	if (block + nsect > get_capacity(req->rq_disk))
 		return 0;

 	switch(rq_data_dir(req)) {
 	case READ:
 		for (; nsect > 0; nsect--, block++, buf += 512)
 			if (tr->readsect(dev, block, buf))
 				return 0;
 		return 1;

 	case WRITE:
 		if (!tr->writesect)
 			return 0;

 		for (; nsect > 0; nsect--, block++, buf += 512)
 			if (tr->writesect(dev, block, buf))
 				return 0;
 		return 1;

 	default:
 		printk(KERN_NOTICE "Unknown request %ld\n", rq_data_dir(req));
 		return 0;
 	}
 }

 static int mtd_blktrans_thread(void *arg)
 {
 	struct mtd_blktrans_ops *tr = arg;
 	struct request_queue *rq = tr->blkcore_priv->rq;

 	/* we might get involved when memory gets low, so use PF_MEMALLOC */
 	current->flags |= PF_MEMALLOC | PF_NOFREEZE;

 	daemonize("%sd", tr->name);

 	/* daemonize() doesn't do this for us since some kernel threads
 	   actually want to deal with signals. We can't just call
 	   exit_sighand() since that'll cause an oops when we finally
 	   do exit. */
 	spin_lock_irq(&current->sighand->siglock);
 	sigfillset(&current->blocked);
 	recalc_sigpending();
 	spin_unlock_irq(&current->sighand->siglock);

 	spin_lock_irq(rq->queue_lock);

 	while (!tr->blkcore_priv->exiting) {
 		struct request *req;
 		struct mtd_blktrans_dev *dev;
 		int res = 0;
 		DECLARE_WAITQUEUE(wait, current);

 		req = elv_next_request(rq);

 		if (!req) {
 			add_wait_queue(&tr->blkcore_priv->thread_wq, &wait);
 			set_current_state(TASK_INTERRUPTIBLE);

 			spin_unlock_irq(rq->queue_lock);

 			schedule();
 			remove_wait_queue(&tr->blkcore_priv->thread_wq, &wait);

 			spin_lock_irq(rq->queue_lock);

 			continue;
 		}

 		dev = req->rq_disk->private_data;
 		tr = dev->tr;

 		spin_unlock_irq(rq->queue_lock);

 		down(&dev->sem);
 		res = do_blktrans_request(tr, dev, req);
 		up(&dev->sem);

 		spin_lock_irq(rq->queue_lock);

 		end_request(req, res);
 	}
 	spin_unlock_irq(rq->queue_lock);

 	complete_and_exit(&tr->blkcore_priv->thread_dead, 0);
 }

 static void mtd_blktrans_request(struct request_queue *rq)
 {
 	struct mtd_blktrans_ops *tr = rq->queuedata;
 	wake_up(&tr->blkcore_priv->thread_wq);
 }


 static int blktrans_open(struct inode *i, struct file *f)
 {
 	struct mtd_blktrans_dev *dev;
 	struct mtd_blktrans_ops *tr;
 	int ret = -ENODEV;

 	dev = i->i_bdev->bd_disk->private_data;
 	tr = dev->tr;

 	if (!try_module_get(dev->mtd->owner))
 		goto out;

 	if (!try_module_get(tr->owner))
 		goto out_tr;

 	/* FIXME: Locking. A hot pluggable device can go away
 	   (del_mtd_device can be called for it) without its module
 	   being unloaded. */
 	dev->mtd->usecount++;

 	ret = 0;
 	if (tr->open && (ret = tr->open(dev))) {
 		dev->mtd->usecount--;
 		module_put(dev->mtd->owner);
 	out_tr:
 		module_put(tr->owner);
 	}
  out:
 	return ret;
 }

 static int blktrans_release(struct inode *i, struct file *f)
 {
 	struct mtd_blktrans_dev *dev;
 	struct mtd_blktrans_ops *tr;
 	int ret = 0;

 	dev = i->i_bdev->bd_disk->private_data;
 	tr = dev->tr;

 	if (tr->release)
 		ret = tr->release(dev);

 	if (!ret) {
 		dev->mtd->usecount--;
 		module_put(dev->mtd->owner);
 		module_put(tr->owner);
 	}

 	return ret;
 }

 static int blktrans_getgeo(struct block_device *bdev, struct hd_geometry *geo)
 {
 	struct mtd_blktrans_dev *dev = bdev->bd_disk->private_data;

 	if (dev->tr->getgeo)
 		return dev->tr->getgeo(dev, geo);
 	return -ENOTTY;
 }

 static int blktrans_ioctl(struct inode *inode, struct file *file,
 			      unsigned int cmd, unsigned long arg)
 {
 	struct mtd_blktrans_dev *dev = inode->i_bdev->bd_disk->private_data;
 	struct mtd_blktrans_ops *tr = dev->tr;

 	switch (cmd) {
 	case BLKFLSBUF:
 		if (tr->flush)
 			return tr->flush(dev);
 		/* The core code did the work, we had nothing to do. */
 		return 0;
 	default:
 		return -ENOTTY;
 	}
 }

 struct block_device_operations mtd_blktrans_ops = {
 	.owner		= THIS_MODULE,
 	.open		= blktrans_open,
 	.release	= blktrans_release,
 	.ioctl		= blktrans_ioctl,
 	.getgeo		= blktrans_getgeo,
 };

 int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
 {
 	struct mtd_blktrans_ops *tr = new->tr;
 	struct list_head *this;
 	int last_devnum = -1;
 	struct gendisk *gd;

 	if (!down_trylock(&mtd_table_mutex)) {
 		up(&mtd_table_mutex);
 		BUG();
 	}

 	list_for_each(this, &tr->devs) {
 		struct mtd_blktrans_dev *d = list_entry(this, struct mtd_blktrans_dev, list);
 		if (new->devnum == -1) {
 			/* Use first free number */
 			if (d->devnum != last_devnum+1) {
 				/* Found a free devnum. Plug it in here */
 				new->devnum = last_devnum+1;
 				list_add_tail(&new->list, &d->list);
 				goto added;
 			}
 		} else if (d->devnum == new->devnum) {
 			/* Required number taken */
 			return -EBUSY;
 		} else if (d->devnum > new->devnum) {
 			/* Required number was free */
 			list_add_tail(&new->list, &d->list);
 			goto added;
 		}
 		last_devnum = d->devnum;
 	}
 	if (new->devnum == -1)
 		new->devnum = last_devnum+1;

 	if ((new->devnum << tr->part_bits) > 256) {
 		return -EBUSY;
 	}

 	init_MUTEX(&new->sem);
 	list_add_tail(&new->list, &tr->devs);
  added:
 	if (!tr->writesect)
 		new->readonly = 1;

 	gd = alloc_disk(1 << tr->part_bits);
 	if (!gd) {
 		list_del(&new->list);
 		return -ENOMEM;
 	}
 	gd->major = tr->major;
 	gd->first_minor = (new->devnum) << tr->part_bits;
 	gd->fops = &mtd_blktrans_ops;

 	if (tr->part_bits)
 		if (new->devnum < 26)
 			snprintf(gd->disk_name, sizeof(gd->disk_name),
 				 "%s%c", tr->name, 'a' + new->devnum);
 		else
 			snprintf(gd->disk_name, sizeof(gd->disk_name),
 				 "%s%c%c", tr->name,
 				 'a' - 1 + new->devnum / 26,
 				 'a' + new->devnum % 26);
 	else
 		snprintf(gd->disk_name, sizeof(gd->disk_name),
 			 "%s%d", tr->name, new->devnum);

 	/* 2.5 has capacity in units of 512 bytes while still
 	   having BLOCK_SIZE_BITS set to 10. Just to keep us amused. */
 	set_capacity(gd, (new->size * new->blksize) >> 9);

 	gd->private_data = new;
 	new->blkcore_priv = gd;
 	gd->queue = tr->blkcore_priv->rq;

 	if (new->readonly)
 		set_disk_ro(gd, 1);

 	add_disk(gd);

 	return 0;
 }

 int del_mtd_blktrans_dev(struct mtd_blktrans_dev *old)
 {
 	if (!down_trylock(&mtd_table_mutex)) {
 		up(&mtd_table_mutex);
 		BUG();
 	}

 	list_del(&old->list);

 	del_gendisk(old->blkcore_priv);
 	put_disk(old->blkcore_priv);

 	return 0;
 }

 static void blktrans_notify_remove(struct mtd_info *mtd)
 {
 	struct list_head *this, *this2, *next;

 	list_for_each(this, &blktrans_majors) {
 		struct mtd_blktrans_ops *tr = list_entry(this, struct mtd_blktrans_ops, list);

 		list_for_each_safe(this2, next, &tr->devs) {
 			struct mtd_blktrans_dev *dev = list_entry(this2, struct mtd_blktrans_dev, list);

 			if (dev->mtd == mtd)
 				tr->remove_dev(dev);
 		}
 	}
 }

 static void blktrans_notify_add(struct mtd_info *mtd)
 {
 	struct list_head *this;

 	if (mtd->type == MTD_ABSENT)
 		return;

 	list_for_each(this, &blktrans_majors) {
 		struct mtd_blktrans_ops *tr = list_entry(this, struct mtd_blktrans_ops, list);

 		tr->add_mtd(tr, mtd);
 	}

 }

 static struct mtd_notifier blktrans_notifier = {
 	.add = blktrans_notify_add,
 	.remove = blktrans_notify_remove,
 };

 int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 {
 	int ret, i;

 	/* Register the notifier if/when the first device type is
 	   registered, to prevent the link/init ordering from fucking
 	   us over. */
 	if (!blktrans_notifier.list.next)
 		register_mtd_user(&blktrans_notifier);

 	tr->blkcore_priv = kmalloc(sizeof(*tr->blkcore_priv), GFP_KERNEL);
 	if (!tr->blkcore_priv)
 		return -ENOMEM;

 	memset(tr->blkcore_priv, 0, sizeof(*tr->blkcore_priv));

 	down(&mtd_table_mutex);

 	ret = register_blkdev(tr->major, tr->name);
 	if (ret) {
 		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
 		       tr->name, tr->major, ret);
 		kfree(tr->blkcore_priv);
 		up(&mtd_table_mutex);
 		return ret;
 	}
 	spin_lock_init(&tr->blkcore_priv->queue_lock);
 	init_completion(&tr->blkcore_priv->thread_dead);
 	init_waitqueue_head(&tr->blkcore_priv->thread_wq);

 	tr->blkcore_priv->rq = blk_init_queue(mtd_blktrans_request, &tr->blkcore_priv->queue_lock);
 	if (!tr->blkcore_priv->rq) {
 		unregister_blkdev(tr->major, tr->name);
 		kfree(tr->blkcore_priv);
 		up(&mtd_table_mutex);
 		return -ENOMEM;
 	}

 	tr->blkcore_priv->rq->queuedata = tr;

 	ret = kernel_thread(mtd_blktrans_thread, tr, CLONE_KERNEL);
 	if (ret < 0) {
 		blk_cleanup_queue(tr->blkcore_priv->rq);
 		unregister_blkdev(tr->major, tr->name);
 		kfree(tr->blkcore_priv);
 		up(&mtd_table_mutex);
 		return ret;
 	}

 	INIT_LIST_HEAD(&tr->devs);
 	list_add(&tr->list, &blktrans_majors);

 	for (i=0; i<MAX_MTD_DEVICES; i++) {
 		if (mtd_table[i] && mtd_table[i]->type != MTD_ABSENT)
 			tr->add_mtd(tr, mtd_table[i]);
 	}

 	up(&mtd_table_mutex);

 	return 0;
 }

 int deregister_mtd_blktrans(struct mtd_blktrans_ops *tr)
 {
 	struct list_head *this, *next;

 	down(&mtd_table_mutex);

 	/* Clean up the kernel thread */
 	tr->blkcore_priv->exiting = 1;
 	wake_up(&tr->blkcore_priv->thread_wq);
 	wait_for_completion(&tr->blkcore_priv->thread_dead);

 	/* Remove it from the list of active majors */
 	list_del(&tr->list);

 	list_for_each_safe(this, next, &tr->devs) {
 		struct mtd_blktrans_dev *dev = list_entry(this, struct mtd_blktrans_dev, list);
 		tr->remove_dev(dev);
 	}

 	blk_cleanup_queue(tr->blkcore_priv->rq);
 	unregister_blkdev(tr->major, tr->name);

 	up(&mtd_table_mutex);

 	kfree(tr->blkcore_priv);

 	BUG_ON(!list_empty(&tr->devs));
 	return 0;
 }

 static void __exit mtd_blktrans_exit(void)
 {
 	/* No race here -- if someone's currently in register_mtd_blktrans
 	   we're screwed anyway. */
 	if (blktrans_notifier.list.next)
 		unregister_mtd_user(&blktrans_notifier);
 }

 module_exit(mtd_blktrans_exit);

 EXPORT_SYMBOL_GPL(register_mtd_blktrans);
 EXPORT_SYMBOL_GPL(deregister_mtd_blktrans);
 EXPORT_SYMBOL_GPL(add_mtd_blktrans_dev);
 EXPORT_SYMBOL_GPL(del_mtd_blktrans_dev);

 MODULE_AUTHOR("David Woodhouse <dwmw2@infradead.org>");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("Common interface to block layer for MTD 'translation layers'");
	/*
	* $Id: mtd_blkdevs.c,v 1.27 2005/11/07 11:14:20 gleixner Exp $
	*
	* (C) 2003 David Woodhouse <dwmw2@infradead.org>
	*
	* Interface to Linux 2.5 block layer for MTD 'translation layers'.
	*
	*/

	#include <linux/kernel.h>
	#include <linux/slab.h>
	#include <linux/module.h>
	#include <linux/list.h>
	#include <linux/fs.h>
	#include <linux/mtd/blktrans.h>
	#include <linux/mtd/mtd.h>
	#include <linux/blkdev.h>
	#include <linux/blkpg.h>
	#include <linux/spinlock.h>
	#include <linux/hdreg.h>
	#include <linux/init.h>
	#include <asm/semaphore.h>
	#include <asm/uaccess.h>

	static LIST_HEAD(blktrans_majors);

	extern struct semaphore mtd_table_mutex;
	extern struct mtd_info *mtd_table[];

	struct mtd_blkcore_priv {
	struct completion thread_dead;
	int exiting;
	wait_queue_head_t thread_wq;
	struct request_queue *rq;
	spinlock_t queue_lock;
	};

	static int do_blktrans_request(struct mtd_blktrans_ops *tr,
	struct mtd_blktrans_dev *dev,
	struct request *req)
	{
	unsigned long block, nsect;
	char *buf;

	block = req->sector;
	nsect = req->current_nr_sectors;
	buf = req->buffer;

	if (!(req->flags & REQ_CMD))
	return 0;

	if (block + nsect > get_capacity(req->rq_disk))
	return 0;

	switch(rq_data_dir(req)) {
	case READ:
	for (; nsect > 0; nsect--, block++, buf += 512)
	if (tr->readsect(dev, block, buf))
	return 0;
	return 1;

	case WRITE:
	if (!tr->writesect)
	return 0;

	for (; nsect > 0; nsect--, block++, buf += 512)
	if (tr->writesect(dev, block, buf))
	return 0;
	return 1;

	default:
	printk(KERN_NOTICE "Unknown request %ld\n", rq_data_dir(req));
	return 0;
	}
	}

	static int mtd_blktrans_thread(void *arg)
	{
	struct mtd_blktrans_ops *tr = arg;
	struct request_queue *rq = tr->blkcore_priv->rq;

	/* we might get involved when memory gets low, so use PF_MEMALLOC */
	current->flags \|= PF_MEMALLOC \| PF_NOFREEZE;

	daemonize("%sd", tr->name);

	/* daemonize() doesn't do this for us since some kernel threads
	actually want to deal with signals. We can't just call
	exit_sighand() since that'll cause an oops when we finally
	do exit. */
	spin_lock_irq(&current->sighand->siglock);
	sigfillset(&current->blocked);
	recalc_sigpending();
	spin_unlock_irq(&current->sighand->siglock);

	spin_lock_irq(rq->queue_lock);

	while (!tr->blkcore_priv->exiting) {
	struct request *req;
	struct mtd_blktrans_dev *dev;
	int res = 0;
	DECLARE_WAITQUEUE(wait, current);

	req = elv_next_request(rq);

	if (!req) {
	add_wait_queue(&tr->blkcore_priv->thread_wq, &wait);
	set_current_state(TASK_INTERRUPTIBLE);

	spin_unlock_irq(rq->queue_lock);

	schedule();
	remove_wait_queue(&tr->blkcore_priv->thread_wq, &wait);

	spin_lock_irq(rq->queue_lock);

	continue;
	}

	dev = req->rq_disk->private_data;
	tr = dev->tr;

	spin_unlock_irq(rq->queue_lock);

	down(&dev->sem);
	res = do_blktrans_request(tr, dev, req);
	up(&dev->sem);

	spin_lock_irq(rq->queue_lock);

	end_request(req, res);
	}
	spin_unlock_irq(rq->queue_lock);

	complete_and_exit(&tr->blkcore_priv->thread_dead, 0);
	}

	static void mtd_blktrans_request(struct request_queue *rq)
	{
	struct mtd_blktrans_ops *tr = rq->queuedata;
	wake_up(&tr->blkcore_priv->thread_wq);
	}


	static int blktrans_open(struct inode i, struct file f)
	{
	struct mtd_blktrans_dev *dev;
	struct mtd_blktrans_ops *tr;
	int ret = -ENODEV;

	dev = i->i_bdev->bd_disk->private_data;
	tr = dev->tr;

	if (!try_module_get(dev->mtd->owner))
	goto out;

	if (!try_module_get(tr->owner))
	goto out_tr;

	/* FIXME: Locking. A hot pluggable device can go away
	(del_mtd_device can be called for it) without its module
	being unloaded. */
	dev->mtd->usecount++;

	ret = 0;
	if (tr->open && (ret = tr->open(dev))) {
	dev->mtd->usecount--;
	module_put(dev->mtd->owner);
	out_tr:
	module_put(tr->owner);
	}
	out:
	return ret;
	}

	static int blktrans_release(struct inode i, struct file f)
	{
	struct mtd_blktrans_dev *dev;
	struct mtd_blktrans_ops *tr;
	int ret = 0;

	dev = i->i_bdev->bd_disk->private_data;
	tr = dev->tr;

	if (tr->release)
	ret = tr->release(dev);

	if (!ret) {
	dev->mtd->usecount--;
	module_put(dev->mtd->owner);
	module_put(tr->owner);
	}

	return ret;
	}

	static int blktrans_getgeo(struct block_device bdev, struct hd_geometry geo)
	{
	struct mtd_blktrans_dev *dev = bdev->bd_disk->private_data;

	if (dev->tr->getgeo)
	return dev->tr->getgeo(dev, geo);
	return -ENOTTY;
	}

	static int blktrans_ioctl(struct inode inode, struct file file,
	unsigned int cmd, unsigned long arg)
	{
	struct mtd_blktrans_dev *dev = inode->i_bdev->bd_disk->private_data;
	struct mtd_blktrans_ops *tr = dev->tr;

	switch (cmd) {
	case BLKFLSBUF:
	if (tr->flush)
	return tr->flush(dev);
	/* The core code did the work, we had nothing to do. */
	return 0;
	default:
	return -ENOTTY;
	}
	}

	struct block_device_operations mtd_blktrans_ops = {
	.owner = THIS_MODULE,
	.open = blktrans_open,
	.release = blktrans_release,
	.ioctl = blktrans_ioctl,
	.getgeo = blktrans_getgeo,
	};

	int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
	{
	struct mtd_blktrans_ops *tr = new->tr;
	struct list_head *this;
	int last_devnum = -1;
	struct gendisk *gd;

	if (!down_trylock(&mtd_table_mutex)) {
	up(&mtd_table_mutex);
	BUG();
	}

	list_for_each(this, &tr->devs) {
	struct mtd_blktrans_dev *d = list_entry(this, struct mtd_blktrans_dev, list);
	if (new->devnum == -1) {
	/* Use first free number */
	if (d->devnum != last_devnum+1) {
	/* Found a free devnum. Plug it in here */
	new->devnum = last_devnum+1;
	list_add_tail(&new->list, &d->list);
	goto added;
	}
	} else if (d->devnum == new->devnum) {
	/* Required number taken */
	return -EBUSY;
	} else if (d->devnum > new->devnum) {
	/* Required number was free */
	list_add_tail(&new->list, &d->list);
	goto added;
	}
	last_devnum = d->devnum;
	}
	if (new->devnum == -1)
	new->devnum = last_devnum+1;

	if ((new->devnum << tr->part_bits) > 256) {
	return -EBUSY;
	}

	init_MUTEX(&new->sem);
	list_add_tail(&new->list, &tr->devs);
	added:
	if (!tr->writesect)
	new->readonly = 1;

	gd = alloc_disk(1 << tr->part_bits);
	if (!gd) {
	list_del(&new->list);
	return -ENOMEM;
	}
	gd->major = tr->major;
	gd->first_minor = (new->devnum) << tr->part_bits;
	gd->fops = &mtd_blktrans_ops;

	if (tr->part_bits)
	if (new->devnum < 26)
	snprintf(gd->disk_name, sizeof(gd->disk_name),
	"%s%c", tr->name, 'a' + new->devnum);
	else
	snprintf(gd->disk_name, sizeof(gd->disk_name),
	"%s%c%c", tr->name,
	'a' - 1 + new->devnum / 26,
	'a' + new->devnum % 26);
	else
	snprintf(gd->disk_name, sizeof(gd->disk_name),
	"%s%d", tr->name, new->devnum);

	/* 2.5 has capacity in units of 512 bytes while still
	having BLOCK_SIZE_BITS set to 10. Just to keep us amused. */
	set_capacity(gd, (new->size * new->blksize) >> 9);

	gd->private_data = new;
	new->blkcore_priv = gd;
	gd->queue = tr->blkcore_priv->rq;

	if (new->readonly)
	set_disk_ro(gd, 1);

	add_disk(gd);

	return 0;
	}

	int del_mtd_blktrans_dev(struct mtd_blktrans_dev *old)
	{
	if (!down_trylock(&mtd_table_mutex)) {
	up(&mtd_table_mutex);
	BUG();
	}

	list_del(&old->list);

	del_gendisk(old->blkcore_priv);
	put_disk(old->blkcore_priv);

	return 0;
	}

	static void blktrans_notify_remove(struct mtd_info *mtd)
	{
	struct list_head this, this2, *next;

	list_for_each(this, &blktrans_majors) {
	struct mtd_blktrans_ops *tr = list_entry(this, struct mtd_blktrans_ops, list);

	list_for_each_safe(this2, next, &tr->devs) {
	struct mtd_blktrans_dev *dev = list_entry(this2, struct mtd_blktrans_dev, list);

	if (dev->mtd == mtd)
	tr->remove_dev(dev);
	}
	}
	}

	static void blktrans_notify_add(struct mtd_info *mtd)
	{
	struct list_head *this;

	if (mtd->type == MTD_ABSENT)
	return;

	list_for_each(this, &blktrans_majors) {
	struct mtd_blktrans_ops *tr = list_entry(this, struct mtd_blktrans_ops, list);

	tr->add_mtd(tr, mtd);
	}

	}

	static struct mtd_notifier blktrans_notifier = {
	.add = blktrans_notify_add,
	.remove = blktrans_notify_remove,
	};

	int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
	{
	int ret, i;

	/* Register the notifier if/when the first device type is
	registered, to prevent the link/init ordering from fucking
	us over. */
	if (!blktrans_notifier.list.next)
	register_mtd_user(&blktrans_notifier);

	tr->blkcore_priv = kmalloc(sizeof(*tr->blkcore_priv), GFP_KERNEL);
	if (!tr->blkcore_priv)
	return -ENOMEM;

	memset(tr->blkcore_priv, 0, sizeof(*tr->blkcore_priv));

	down(&mtd_table_mutex);

	ret = register_blkdev(tr->major, tr->name);
	if (ret) {
	printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
	tr->name, tr->major, ret);
	kfree(tr->blkcore_priv);
	up(&mtd_table_mutex);
	return ret;
	}
	spin_lock_init(&tr->blkcore_priv->queue_lock);
	init_completion(&tr->blkcore_priv->thread_dead);
	init_waitqueue_head(&tr->blkcore_priv->thread_wq);

	tr->blkcore_priv->rq = blk_init_queue(mtd_blktrans_request, &tr->blkcore_priv->queue_lock);
	if (!tr->blkcore_priv->rq) {
	unregister_blkdev(tr->major, tr->name);
	kfree(tr->blkcore_priv);
	up(&mtd_table_mutex);
	return -ENOMEM;
	}

	tr->blkcore_priv->rq->queuedata = tr;

	ret = kernel_thread(mtd_blktrans_thread, tr, CLONE_KERNEL);
	if (ret < 0) {
	blk_cleanup_queue(tr->blkcore_priv->rq);
	unregister_blkdev(tr->major, tr->name);
	kfree(tr->blkcore_priv);
	up(&mtd_table_mutex);
	return ret;
	}

	INIT_LIST_HEAD(&tr->devs);
	list_add(&tr->list, &blktrans_majors);

	for (i=0; i<MAX_MTD_DEVICES; i++) {
	if (mtd_table[i] && mtd_table[i]->type != MTD_ABSENT)
	tr->add_mtd(tr, mtd_table[i]);
	}

	up(&mtd_table_mutex);

	return 0;
	}

	int deregister_mtd_blktrans(struct mtd_blktrans_ops *tr)
	{
	struct list_head this, next;

	down(&mtd_table_mutex);

	/* Clean up the kernel thread */
	tr->blkcore_priv->exiting = 1;
	wake_up(&tr->blkcore_priv->thread_wq);
	wait_for_completion(&tr->blkcore_priv->thread_dead);

	/* Remove it from the list of active majors */
	list_del(&tr->list);

	list_for_each_safe(this, next, &tr->devs) {
	struct mtd_blktrans_dev *dev = list_entry(this, struct mtd_blktrans_dev, list);
	tr->remove_dev(dev);
	}

	blk_cleanup_queue(tr->blkcore_priv->rq);
	unregister_blkdev(tr->major, tr->name);

	up(&mtd_table_mutex);

	kfree(tr->blkcore_priv);

	BUG_ON(!list_empty(&tr->devs));
	return 0;
	}

	static void __exit mtd_blktrans_exit(void)
	{
	/* No race here -- if someone's currently in register_mtd_blktrans
	we're screwed anyway. */
	if (blktrans_notifier.list.next)
	unregister_mtd_user(&blktrans_notifier);
	}

	module_exit(mtd_blktrans_exit);

	EXPORT_SYMBOL_GPL(register_mtd_blktrans);
	EXPORT_SYMBOL_GPL(deregister_mtd_blktrans);
	EXPORT_SYMBOL_GPL(add_mtd_blktrans_dev);
	EXPORT_SYMBOL_GPL(del_mtd_blktrans_dev);

	MODULE_AUTHOR("David Woodhouse <dwmw2@infradead.org>");
	MODULE_LICENSE("GPL");
	MODULE_DESCRIPTION("Common interface to block layer for MTD 'translation layers'");