printer.c

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	int timeout, err = 0, writecount = 0;

	while (writecount < count) {

		if (usblp->writeurb.status == -EINPROGRESS) {

			if (file->f_flags & O_NONBLOCK)
				return -EAGAIN;

			timeout = USBLP_WRITE_TIMEOUT;
			while (timeout && usblp->writeurb.status == -EINPROGRESS) {

				if (signal_pending(current))
					return writecount ? writecount : -EINTR;

				timeout = interruptible_sleep_on_timeout(&usblp->wait, timeout);
			}
		}

		if (!usblp->dev)
			return -ENODEV;

		if (usblp->writeurb.status) {
			if (usblp->quirks & USBLP_QUIRK_BIDIR) {
				if (usblp->writeurb.status != -EINPROGRESS)
					err("usblp%d: error %d writing to printer",
						usblp->minor, usblp->writeurb.status);
				err = usblp->writeurb.status;
				continue;
			}
			else {
				err = usblp_check_status(usblp, err);
				continue;
			}
		}

		writecount += usblp->writeurb.transfer_buffer_length;
		usblp->writeurb.transfer_buffer_length = 0;

		if (writecount == count)
			continue;

		usblp->writeurb.transfer_buffer_length = (count - writecount) < USBLP_BUF_SIZE ?
							 (count - writecount) : USBLP_BUF_SIZE;

		if (copy_from_user(usblp->writeurb.transfer_buffer, buffer + writecount,
				usblp->writeurb.transfer_buffer_length)) return -EFAULT;

		usblp->writeurb.dev = usblp->dev;
		usb_submit_urb(&usblp->writeurb);
	}

	return count;
}

static ssize_t usblp_read(struct file *file, char *buffer, size_t count, loff_t *ppos)
{
	struct usblp *usblp = file->private_data;

	if (!usblp->bidir)
		return -EINVAL;

	if (usblp->readurb.status == -EINPROGRESS) {

		if (file->f_flags & O_NONBLOCK)
			return -EAGAIN;

		while (usblp->readurb.status == -EINPROGRESS) {
			if (signal_pending(current))
				return -EINTR;
			interruptible_sleep_on(&usblp->wait);
		}
	}

	if (!usblp->dev)
		return -ENODEV;

	if (usblp->readurb.status) {
		err("usblp%d: error %d reading from printer",
			usblp->minor, usblp->readurb.status);
		usblp->readurb.dev = usblp->dev;
		usb_submit_urb(&usblp->readurb);
		return -EIO;
	}

	count = count < usblp->readurb.actual_length - usblp->readcount ?
		count :	usblp->readurb.actual_length - usblp->readcount;

	if (copy_to_user(buffer, usblp->readurb.transfer_buffer + usblp->readcount, count))
		return -EFAULT;

	if ((usblp->readcount += count) == usblp->readurb.actual_length) {
		usblp->readcount = 0;
		usblp->readurb.dev = usblp->dev;
		usb_submit_urb(&usblp->readurb);
	}

	return count;
}

/*
 * Checks for printers that have quirks, such as requiring unidirectional
 * communication but reporting bidirectional; currently some HP printers
 * have this flaw (HP 810, 880, 895, etc.), or needing an init string
 * sent at each open (like some Epsons).
 * Returns 1 if found, 0 if not found.
 *
 * HP recommended that we use the bidirectional interface but
 * don't attempt any bulk IN transfers from the IN endpoint.
 * Here's some more detail on the problem:
 * The problem is not that it isn't bidirectional though. The problem
 * is that if you request a device ID, or status information, while
 * the buffers are full, the return data will end up in the print data
 * buffer. For example if you make sure you never request the device ID
 * while you are sending print data, and you don't try to query the
 * printer status every couple of milliseconds, you will probably be OK.
 */
static unsigned int usblp_quirks (__u16 vendor, __u16 product)
{
	int i;

	for (i = 0; quirk_printers[i].vendorId; i++) {
		if (vendor == quirk_printers[i].vendorId &&
		    product == quirk_printers[i].productId)
			return quirk_printers[i].quirks;
 	}
	return 0;
}

static void *usblp_probe(struct usb_device *dev, unsigned int ifnum,
			 const struct usb_device_id *id)
{
	struct usb_interface_descriptor *interface;
	struct usb_endpoint_descriptor *epread, *epwrite;
	struct usblp *usblp;
	int minor, i, bidir = 0, quirks;
	int alts = dev->actconfig->interface[ifnum].act_altsetting;
	int length, err;
	char *buf;

	/* If a bidirectional interface exists, use it. */
	for (i = 0; i < dev->actconfig->interface[ifnum].num_altsetting; i++) {

		interface = &dev->actconfig->interface[ifnum].altsetting[i];

		if (interface->bInterfaceClass != 7 || interface->bInterfaceSubClass != 1 ||
		    interface->bInterfaceProtocol < 1 || interface->bInterfaceProtocol > 3 ||
		   (interface->bInterfaceProtocol > 1 && interface->bNumEndpoints < 2))
			continue;

		if (interface->bInterfaceProtocol > 1) {
			bidir = 1;
			alts = i;
			break;
		}
	}

	interface = &dev->actconfig->interface[ifnum].altsetting[alts];
	if (usb_set_interface(dev, ifnum, alts))
		err("can't set desired altsetting %d on interface %d", alts, ifnum);

	epwrite = interface->endpoint + 0;
	epread = bidir ? interface->endpoint + 1 : NULL;

	if ((epwrite->bEndpointAddress & 0x80) == 0x80) {
		if (interface->bNumEndpoints == 1)
			return NULL;
		epwrite = interface->endpoint + 1;
		epread = bidir ? interface->endpoint + 0 : NULL;
	}

	if ((epwrite->bEndpointAddress & 0x80) == 0x80)
		return NULL;

	if (bidir && (epread->bEndpointAddress & 0x80) != 0x80)
		return NULL;

	for (minor = 0; minor < USBLP_MINORS && usblp_table[minor]; minor++);
	if (usblp_table[minor]) {
		err("no more free usblp devices");
		return NULL;
	}

	if (!(usblp = kmalloc(sizeof(struct usblp), GFP_KERNEL))) {
		err("out of memory");
		return NULL;
	}
	memset(usblp, 0, sizeof(struct usblp));

	/* lookup quirks for this printer */
	quirks = usblp_quirks(dev->descriptor.idVendor, dev->descriptor.idProduct);

	if (bidir && (quirks & USBLP_QUIRK_BIDIR)) {
		bidir = 0;
		epread = NULL;
		info ("Disabling reads from problem bidirectional printer on usblp%d",
			minor);
	}

	usblp->dev = dev;
	usblp->ifnum = ifnum;
	usblp->minor = minor;
	usblp->bidir = bidir;
	usblp->quirks = quirks;

	init_waitqueue_head(&usblp->wait);

	if (!(buf = kmalloc(USBLP_BUF_SIZE * (bidir ? 2 : 1), GFP_KERNEL))) {
		err("out of memory");
		kfree(usblp);
		return NULL;
	}

	if (!(usblp->device_id_string = kmalloc(DEVICE_ID_SIZE, GFP_KERNEL))) {
		err("out of memory");
		kfree(usblp);
		kfree(buf);
		return NULL;
	}

	FILL_BULK_URB(&usblp->writeurb, dev, usb_sndbulkpipe(dev, epwrite->bEndpointAddress),
		buf, 0, usblp_bulk, usblp);

	if (bidir)
		FILL_BULK_URB(&usblp->readurb, dev, usb_rcvbulkpipe(dev, epread->bEndpointAddress),
			buf + USBLP_BUF_SIZE, USBLP_BUF_SIZE, usblp_bulk, usblp);

	/* Get the device_id string if possible. FIXME: Could make this kmalloc(length). */
	err = usblp_get_id(usblp, 0, usblp->device_id_string, DEVICE_ID_SIZE - 1);
	if (err >= 0) {
		length = (usblp->device_id_string[0] << 8) + usblp->device_id_string[1]; /* big-endian */
		if (length < DEVICE_ID_SIZE)
			usblp->device_id_string[length] = '\0';
		else
			usblp->device_id_string[DEVICE_ID_SIZE - 1] = '\0';
		dbg ("usblp%d Device ID string [%d]=%s",
			minor, length, &usblp->device_id_string[2]);
	}
	else {
		err ("usblp%d: error = %d reading IEEE-1284 Device ID string",
			minor, err);
		usblp->device_id_string[0] = usblp->device_id_string[1] = '\0';
	}

#ifdef DEBUG
	usblp_check_status(usblp, 0);
#endif

	info("usblp%d: USB %sdirectional printer dev %d if %d alt %d",
		minor, bidir ? "Bi" : "Uni", dev->devnum, ifnum, alts);

	return usblp_table[minor] = usblp;
}

static void usblp_disconnect(struct usb_device *dev, void *ptr)
{
	struct usblp *usblp = ptr;

	if (!usblp || !usblp->dev) {
		err("disconnect on nonexisting interface");
		return;
	}

	usblp->dev = NULL;

	usb_unlink_urb(&usblp->writeurb);
	if (usblp->bidir)
		usb_unlink_urb(&usblp->readurb);

	kfree(usblp->writeurb.transfer_buffer);

	if (usblp->used) return;

	kfree(usblp->device_id_string);

	usblp_table[usblp->minor] = NULL;
	kfree(usblp);
}

static struct file_operations usblp_fops = {
	owner:		THIS_MODULE,
	read:		usblp_read,
	write:		usblp_write,
	poll:		usblp_poll,
	ioctl:		usblp_ioctl,
	open:		usblp_open,
	release:	usblp_release,
};

static struct usb_device_id usblp_ids [] = {
	{ USB_INTERFACE_INFO(7, 1, 1) },
	{ USB_INTERFACE_INFO(7, 1, 2) },
	{ USB_INTERFACE_INFO(7, 1, 3) },
	{ }						/* Terminating entry */
};

MODULE_DEVICE_TABLE (usb, usblp_ids);

static struct usb_driver usblp_driver = {
	name:		"usblp",
	probe:		usblp_probe,
	disconnect:	usblp_disconnect,
	fops:		&usblp_fops,
	minor:		USBLP_MINOR_BASE,
	id_table:	usblp_ids,
};

static int __init usblp_init(void)
{
	if (usb_register(&usblp_driver))
		return -1;
	return 0;
}

static void __exit usblp_exit(void)
{
	usb_deregister(&usblp_driver);
}

module_init(usblp_init);
module_exit(usblp_exit);

MODULE_AUTHOR("Michael Gee, Pavel Machek, Vojtech Pavlik, Randy Dunlap");
MODULE_DESCRIPTION("USB Printer Device Class driver");