static int hot_add_disk(struct mddev *mddev, dev_t dev)

	rdev = md_import_device(dev, -1, 0);
	if (IS_ERR(rdev)) {
		pr_warn("md: error, md_import_device() returned %ld\n",
			PTR_ERR(rdev));
		return -EINVAL;
	}

static struct md_rdev *md_import_device(dev_t newdev, int super_format, int super_minor)
{

    	err = lock_rdev(rdev, newdev, super_format == -2);
	if (err)
		goto abort_free;


    static int lock_rdev(struct md_rdev *rdev, dev_t dev, int shared)
{
	int err = 0;
	struct block_device *bdev;
	char b[BDEVNAME_SIZE];

//
	bdev = blkdev_get_by_dev(dev, FMODE_READ|FMODE_WRITE|FMODE_EXCL,
				 shared ? (struct md_rdev *)lock_rdev : rdev);
	if (IS_ERR(bdev)) {
		pr_warn("md: could not open %s.\n", __bdevname(dev, b));
		return PTR_ERR(bdev);
	}
	rdev->bdev = bdev;
	return err;
}



/**
 * blkdev_get_by_dev - open a block device by device number
 * @dev: device number of block device to open
 * @mode: FMODE_* mask
 * @holder: exclusive holder identifier
 *
 * Open the blockdevice described by device number @dev.  @mode and
 * @holder are identical to blkdev_get().
 *
 * Use it ONLY if you really do not have anything better - i.e. when
 * you are behind a truly sucky interface and all you are given is a
 * device number.  _Never_ to be used for internal purposes.  If you
 * ever need it - reconsider your API.
 *
 * On success, the returned block_device has reference count of one.
 *
 * CONTEXT:
 * Might sleep.
 *
 * RETURNS:
 * Pointer to block_device on success, ERR_PTR(-errno) on failure.
 */
struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
{
	struct block_device *bdev;
	int err;

	bdev = bdget(dev);
	if (!bdev)
		return ERR_PTR(-ENOMEM);

	err = blkdev_get(bdev, mode, holder);
	if (err)
		return ERR_PTR(err);

	return bdev;
}
EXPORT_SYMBOL(blkdev_get_by_dev);

	blk_queue_make_request(mddev->queue, md_make_request);
	blk_set_stacking_limits(&mddev->queue->limits);

static const struct block_device_operations md_fops =
{
	.owner		= THIS_MODULE,
	.open		= md_open,
	.release	= md_release,
	.ioctl		= md_ioctl,
#ifdef CONFIG_COMPAT
	.compat_ioctl	= md_compat_ioctl,
#endif
	.getgeo		= md_getgeo,
	.media_changed  = md_media_changed,
	.revalidate_disk= md_revalidate,
};

    static int md_alloc(dev_t dev, char *name)
{
	/*
	 * If dev is zero, name is the name of a device to allocate with
	 * an arbitrary minor number.  It will be "md_???"
	 * If dev is non-zero it must be a device number with a MAJOR of
	 * MD_MAJOR or mdp_major.  In this case, if "name" is NULL, then
	 * the device is being created by opening a node in /dev.
	 * If "name" is not NULL, the device is being created by
	 * writing to /sys/module/md_mod/parameters/new_array.
	 */
	static DEFINE_MUTEX(disks_mutex);
	struct mddev *mddev = mddev_find_or_alloc(dev);
	struct gendisk *disk;
	int partitioned;
	int shift;
	int unit;
	int error;

	if (!mddev)
		return -ENODEV;

	partitioned = (MAJOR(mddev->unit) != MD_MAJOR);
	shift = partitioned ? MdpMinorShift : 0;
	unit = MINOR(mddev->unit) >> shift;

	/* wait for any previous instance of this device to be
	 * completely removed (mddev_delayed_delete).
	 */
	flush_workqueue(md_misc_wq);

	mutex_lock(&disks_mutex);
	error = -EEXIST;
	if (mddev->gendisk)
		goto abort;

	if (name && !dev) {
		/* Need to ensure that 'name' is not a duplicate.
		 */
		struct mddev *mddev2;
		spin_lock(&all_mddevs_lock);

		list_for_each_entry(mddev2, &all_mddevs, all_mddevs)
			if (mddev2->gendisk &&
			    strcmp(mddev2->gendisk->disk_name, name) == 0) {
				spin_unlock(&all_mddevs_lock);
				goto abort;
			}
		spin_unlock(&all_mddevs_lock);
	}
	if (name && dev)
		/*
		 * Creating /dev/mdNNN via "newarray", so adjust hold_active.
		 */
		mddev->hold_active = UNTIL_STOP;

	error = -ENOMEM;
	mddev->queue = blk_alloc_queue(GFP_KERNEL);
	if (!mddev->queue)
		goto abort;
	mddev->queue->queuedata = mddev;

	blk_queue_make_request(mddev->queue, md_make_request);
	blk_set_stacking_limits(&mddev->queue->limits);

	disk = alloc_disk(1 << shift);
	if (!disk) {
		blk_cleanup_queue(mddev->queue);
		mddev->queue = NULL;
		goto abort;
	}
	disk->major = MAJOR(mddev->unit);
	disk->first_minor = unit << shift;
	if (name)
		strcpy(disk->disk_name, name);
	else if (partitioned)
		sprintf(disk->disk_name, "md_d%d", unit);
	else
		sprintf(disk->disk_name, "md%d", unit);
	disk->fops = &md_fops;
	disk->private_data = mddev;
	disk->queue = mddev->queue;
	blk_queue_write_cache(mddev->queue, true, true);
	/* Allow extended partitions.  This makes the
	 * 'mdp' device redundant, but we can't really
	 * remove it now.
	 */
	disk->flags |= GENHD_FL_EXT_DEVT;
	mddev->gendisk = disk;
	add_disk(disk);

	error = kobject_add(&mddev->kobj, &disk_to_dev(disk)->kobj, "%s", "md");
	if (error) {
		/* This isn't possible, but as kobject_init_and_add is marked
		 * __must_check, we must do something with the result
		 */
		pr_debug("md: cannot register %s/md - name in use\n",
			 disk->disk_name);
		error = 0;
	}
	if (mddev->kobj.sd &&
	    sysfs_create_group(&mddev->kobj, &md_bitmap_group))
		pr_debug("pointless warning\n");
 abort:
	mutex_unlock(&disks_mutex);
	if (!error && mddev->kobj.sd) {
		kobject_uevent(&mddev->kobj, KOBJ_ADD);
		mddev->sysfs_state = sysfs_get_dirent_safe(mddev->kobj.sd, "array_state");
	}
	mddev_put(mddev);
	return error;
}


void md_handle_request(struct mddev *mddev, struct bio *bio)
{
check_suspended:
	rcu_read_lock();
	if (is_suspended(mddev, bio)) {
		DEFINE_WAIT(__wait);
		for (;;) {
			prepare_to_wait(&mddev->sb_wait, &__wait,
					TASK_UNINTERRUPTIBLE);
			if (!is_suspended(mddev, bio))
				break;
			rcu_read_unlock();
			schedule();
			rcu_read_lock();
		}
		finish_wait(&mddev->sb_wait, &__wait);
	}
	atomic_inc(&mddev->active_io);
	rcu_read_unlock();

	if (!mddev->pers->make_request(mddev, bio)) {
		atomic_dec(&mddev->active_io);
		wake_up(&mddev->sb_wait);
		goto check_suspended;
	}

	if (atomic_dec_and_test(&mddev->active_io) && mddev->suspended)
		wake_up(&mddev->sb_wait);
}
EXPORT_SYMBOL(md_handle_request);


/**
 * blk_queue_make_request - define an alternate make_request function for a device
 * @q:  the request queue for the device to be affected
 * @mfn: the alternate make_request function
 *
 * Description:
 *    The normal way for &struct bios to be passed to a device
 *    driver is for them to be collected into requests on a request
 *    queue, and then to allow the device driver to select requests
 *    off that queue when it is ready.  This works well for many block
 *    devices. However some block devices (typically virtual devices
 *    such as md or lvm) do not benefit from the processing on the
 *    request queue, and are served best by having the requests passed
 *    directly to them.  This can be achieved by providing a function
 *    to blk_queue_make_request().
 *
 * Caveat:
 *    The driver that does this *must* be able to deal appropriately
 *    with buffers in "highmemory". This can be accomplished by either calling
 *    kmap_atomic() to get a temporary kernel mapping, or by calling
 *    blk_queue_bounce() to create a buffer in normal memory.
 **/
void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
{
	/*
	 * set defaults
	 */
	q->nr_requests = BLKDEV_MAX_RQ;

	q->make_request_fn = mfn;
	blk_queue_dma_alignment(q, 511);

	blk_set_default_limits(&q->limits);
}