printer_write(struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
{
	struct printer_dev	*dev = fd->private_data;
	unsigned long		flags;
	size_t			size;	/* Amount of data in a TX request. */
	size_t			bytes_copied = 0;
	struct usb_request	*req;
	int			value;

	DBG(dev, "printer_write trying to send %d bytes\n", (int)len);

	if (len == 0)
		return -EINVAL;

	mutex_lock(&dev->lock_printer_io);
	spin_lock_irqsave(&dev->lock, flags);

	if (dev->interface < 0) {
		spin_unlock_irqrestore(&dev->lock, flags);
		mutex_unlock(&dev->lock_printer_io);
		return -ENODEV;
	}

	/* Check if a printer reset happens while we have interrupts on */
	dev->reset_printer = 0;

	/* Check if there is any available write buffers */
	if (likely(list_empty(&dev->tx_reqs))) {
		/* Turn interrupts back on before sleeping. */
		spin_unlock_irqrestore(&dev->lock, flags);

		/*
		 * If write buffers are available check if this is
		 * a NON-Blocking call or not.
		 */
		if (fd->f_flags & (O_NONBLOCK|O_NDELAY)) {
			mutex_unlock(&dev->lock_printer_io);
			return -EAGAIN;
		}

		/* Sleep until a write buffer is available */
		wait_event_interruptible(dev->tx_wait,
				(likely(!list_empty(&dev->tx_reqs))));
		spin_lock_irqsave(&dev->lock, flags);
	}

	while (likely(!list_empty(&dev->tx_reqs)) && len) {

		if (len > USB_BUFSIZE)
			size = USB_BUFSIZE;
		else
			size = len;

		req = container_of(dev->tx_reqs.next, struct usb_request,
				list);
		list_del_init(&req->list);

		req->complete = tx_complete;
		req->length = size;

		/* Check if we need to send a zero length packet. */
		if (len > size)
			/* They will be more TX requests so no yet. */
			req->zero = 0;
		else
			/* If the data amount is not a multiple of the
			 * maxpacket size then send a zero length packet.
			 */
			req->zero = ((len % dev->in_ep->maxpacket) == 0);

		/* Don't leave irqs off while doing memory copies */
		spin_unlock_irqrestore(&dev->lock, flags);

		if (copy_from_user(req->buf, buf, size)) {
			list_add(&req->list, &dev->tx_reqs);
			mutex_unlock(&dev->lock_printer_io);
			return bytes_copied;
		}

		bytes_copied += size;
		len -= size;
		buf += size;

		spin_lock_irqsave(&dev->lock, flags);

		/* We've disconnected or reset so free the req and buffer */
		if (dev->reset_printer) {
			list_add(&req->list, &dev->tx_reqs);
			spin_unlock_irqrestore(&dev->lock, flags);
			mutex_unlock(&dev->lock_printer_io);
			return -EAGAIN;
		}

		list_add(&req->list, &dev->tx_reqs_active);

		/* here, we unlock, and only unlock, to avoid deadlock. */
		spin_unlock(&dev->lock);
		value = usb_ep_queue(dev->in_ep, req, GFP_ATOMIC);
		spin_lock(&dev->lock);
		if (value) {
			list_del(&req->list);
			list_add(&req->list, &dev->tx_reqs);
			spin_unlock_irqrestore(&dev->lock, flags);
			mutex_unlock(&dev->lock_printer_io);
			return -EAGAIN;
		}
	}

	spin_unlock_irqrestore(&dev->lock, flags);
	mutex_unlock(&dev->lock_printer_io);

	DBG(dev, "printer_write sent %d bytes\n", (int)bytes_copied);

	if (bytes_copied)
		return bytes_copied;
	else
		return -EAGAIN;
}