drivers/usb/usb-skeleton.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * USB Skeleton driver - 2.2
  *
  * Copyright (C) 2001-2004 Greg Kroah-Hartman (greg@kroah.com)
  *
  * This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c
  * but has been rewritten to be easier to read and use.
  */

 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/kref.h>
 #include <linux/uaccess.h>
 #include <linux/usb.h>
 #include <linux/mutex.h>


 /* Define these values to match your devices */
 #define USB_SKEL_VENDOR_ID	0xfff0
 #define USB_SKEL_PRODUCT_ID	0xfff0

 /* table of devices that work with this driver */
 static const struct usb_device_id skel_table[] = {
 	{ USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
 	{ }					/* Terminating entry */
 };
 MODULE_DEVICE_TABLE(usb, skel_table);


 /* Get a minor range for your devices from the usb maintainer */
 #define USB_SKEL_MINOR_BASE	192

 /* our private defines. if this grows any larger, use your own .h file */
 #define MAX_TRANSFER		(PAGE_SIZE - 512)
 /* MAX_TRANSFER is chosen so that the VM is not stressed by
    allocations > PAGE_SIZE and the number of packets in a page
    is an integer 512 is the largest possible packet on EHCI */
 #define WRITES_IN_FLIGHT	8
 /* arbitrarily chosen */

 /* Structure to hold all of our device specific stuff */
 struct usb_skel {
 	struct usb_device	*udev;			/* the usb device for this device */
 	struct usb_interface	*interface;		/* the interface for this device */
 	struct semaphore	limit_sem;		/* limiting the number of writes in progress */
 	struct usb_anchor	submitted;		/* in case we need to retract our submissions */
 	struct urb		*bulk_in_urb;		/* the urb to read data with */
 	unsigned char           *bulk_in_buffer;	/* the buffer to receive data */
 	size_t			bulk_in_size;		/* the size of the receive buffer */
 	size_t			bulk_in_filled;		/* number of bytes in the buffer */
 	size_t			bulk_in_copied;		/* already copied to user space */
 	__u8			bulk_in_endpointAddr;	/* the address of the bulk in endpoint */
 	__u8			bulk_out_endpointAddr;	/* the address of the bulk out endpoint */
 	int			errors;			/* the last request tanked */
 	bool			ongoing_read;		/* a read is going on */
 	spinlock_t		err_lock;		/* lock for errors */
 	struct kref		kref;
 	struct mutex		io_mutex;		/* synchronize I/O with disconnect */
 	wait_queue_head_t	bulk_in_wait;		/* to wait for an ongoing read */
 };
 #define to_skel_dev(d) container_of(d, struct usb_skel, kref)

 static struct usb_driver skel_driver;
 static void skel_draw_down(struct usb_skel *dev);

 static void skel_delete(struct kref *kref)
 {
 	struct usb_skel *dev = to_skel_dev(kref);

 	usb_free_urb(dev->bulk_in_urb);
 	usb_put_dev(dev->udev);
 	kfree(dev->bulk_in_buffer);
 	kfree(dev);
 }

 static int skel_open(struct inode *inode, struct file *file)
 {
 	struct usb_skel *dev;
 	struct usb_interface *interface;
 	int subminor;
 	int retval = 0;

 	subminor = iminor(inode);

 	interface = usb_find_interface(&skel_driver, subminor);
 	if (!interface) {
 		pr_err("%s - error, can't find device for minor %d\n",
 			__func__, subminor);
 		retval = -ENODEV;
 		goto exit;
 	}

 	dev = usb_get_intfdata(interface);
 	if (!dev) {
 		retval = -ENODEV;
 		goto exit;
 	}

 	retval = usb_autopm_get_interface(interface);
 	if (retval)
 		goto exit;

 	/* increment our usage count for the device */
 	kref_get(&dev->kref);

 	/* save our object in the file's private structure */
 	file->private_data = dev;

 exit:
 	return retval;
 }

 static int skel_release(struct inode *inode, struct file *file)
 {
 	struct usb_skel *dev;

 	dev = file->private_data;
 	if (dev == NULL)
 		return -ENODEV;

 	/* allow the device to be autosuspended */
 	mutex_lock(&dev->io_mutex);
 	if (dev->interface)
 		usb_autopm_put_interface(dev->interface);
 	mutex_unlock(&dev->io_mutex);

 	/* decrement the count on our device */
 	kref_put(&dev->kref, skel_delete);
 	return 0;
 }

 static int skel_flush(struct file *file, fl_owner_t id)
 {
 	struct usb_skel *dev;
 	int res;

 	dev = file->private_data;
 	if (dev == NULL)
 		return -ENODEV;

 	/* wait for io to stop */
 	mutex_lock(&dev->io_mutex);
 	skel_draw_down(dev);

 	/* read out errors, leave subsequent opens a clean slate */
 	spin_lock_irq(&dev->err_lock);
 	res = dev->errors ? (dev->errors == -EPIPE ? -EPIPE : -EIO) : 0;
 	dev->errors = 0;
 	spin_unlock_irq(&dev->err_lock);

 	mutex_unlock(&dev->io_mutex);

 	return res;
 }

 static void skel_read_bulk_callback(struct urb *urb)
 {
 	struct usb_skel *dev;
 	unsigned long flags;

 	dev = urb->context;

 	spin_lock_irqsave(&dev->err_lock, flags);
 	/* sync/async unlink faults aren't errors */
 	if (urb->status) {
 		if (!(urb->status == -ENOENT ||
 		    urb->status == -ECONNRESET ||
 		    urb->status == -ESHUTDOWN))
 			dev_err(&dev->interface->dev,
 				"%s - nonzero write bulk status received: %d\n",
 				__func__, urb->status);

 		dev->errors = urb->status;
 	} else {
 		dev->bulk_in_filled = urb->actual_length;
 	}
 	dev->ongoing_read = 0;
 	spin_unlock_irqrestore(&dev->err_lock, flags);

 	wake_up_interruptible(&dev->bulk_in_wait);
 }

 static int skel_do_read_io(struct usb_skel *dev, size_t count)
 {
 	int rv;

 	/* prepare a read */
 	usb_fill_bulk_urb(dev->bulk_in_urb,
 			dev->udev,
 			usb_rcvbulkpipe(dev->udev,
 				dev->bulk_in_endpointAddr),
 			dev->bulk_in_buffer,
 			min(dev->bulk_in_size, count),
 			skel_read_bulk_callback,
 			dev);
 	/* tell everybody to leave the URB alone */
 	spin_lock_irq(&dev->err_lock);
 	dev->ongoing_read = 1;
 	spin_unlock_irq(&dev->err_lock);

 	/* submit bulk in urb, which means no data to deliver */
 	dev->bulk_in_filled = 0;
 	dev->bulk_in_copied = 0;

 	/* do it */
 	rv = usb_submit_urb(dev->bulk_in_urb, GFP_KERNEL);
 	if (rv < 0) {
 		dev_err(&dev->interface->dev,
 			"%s - failed submitting read urb, error %d\n",
 			__func__, rv);
 		rv = (rv == -ENOMEM) ? rv : -EIO;
 		spin_lock_irq(&dev->err_lock);
 		dev->ongoing_read = 0;
 		spin_unlock_irq(&dev->err_lock);
 	}

 	return rv;
 }

 static ssize_t skel_read(struct file *file, char *buffer, size_t count,
 			 loff_t *ppos)
 {
 	struct usb_skel *dev;
 	int rv;
 	bool ongoing_io;

 	dev = file->private_data;

 	/* if we cannot read at all, return EOF */
 	if (!dev->bulk_in_urb || !count)
 		return 0;

 	/* no concurrent readers */
 	rv = mutex_lock_interruptible(&dev->io_mutex);
 	if (rv < 0)
 		return rv;

 	if (!dev->interface) {		/* disconnect() was called */
 		rv = -ENODEV;
 		goto exit;
 	}

 	/* if IO is under way, we must not touch things */
 retry:
 	spin_lock_irq(&dev->err_lock);
 	ongoing_io = dev->ongoing_read;
 	spin_unlock_irq(&dev->err_lock);

 	if (ongoing_io) {
 		/* nonblocking IO shall not wait */
 		if (file->f_flags & O_NONBLOCK) {
 			rv = -EAGAIN;
 			goto exit;
 		}
 		/*
 		 * IO may take forever
 		 * hence wait in an interruptible state
 		 */
 		rv = wait_event_interruptible(dev->bulk_in_wait, (!dev->ongoing_read));
 		if (rv < 0)
 			goto exit;
 	}

 	/* errors must be reported */
 	rv = dev->errors;
 	if (rv < 0) {
 		/* any error is reported once */
 		dev->errors = 0;
 		/* to preserve notifications about reset */
 		rv = (rv == -EPIPE) ? rv : -EIO;
 		/* report it */
 		goto exit;
 	}

 	/*
 	 * if the buffer is filled we may satisfy the read
 	 * else we need to start IO
 	 */

 	if (dev->bulk_in_filled) {
 		/* we had read data */
 		size_t available = dev->bulk_in_filled - dev->bulk_in_copied;
 		size_t chunk = min(available, count);

 		if (!available) {
 			/*
 			 * all data has been used
 			 * actual IO needs to be done
 			 */
 			rv = skel_do_read_io(dev, count);
 			if (rv < 0)
 				goto exit;
 			else
 				goto retry;
 		}
 		/*
 		 * data is available
 		 * chunk tells us how much shall be copied
 		 */

 		if (copy_to_user(buffer,
 				 dev->bulk_in_buffer + dev->bulk_in_copied,
 				 chunk))
 			rv = -EFAULT;
 		else
 			rv = chunk;

 		dev->bulk_in_copied += chunk;

 		/*
 		 * if we are asked for more than we have,
 		 * we start IO but don't wait
 		 */
 		if (available < count)
 			skel_do_read_io(dev, count - chunk);
 	} else {
 		/* no data in the buffer */
 		rv = skel_do_read_io(dev, count);
 		if (rv < 0)
 			goto exit;
 		else
 			goto retry;
 	}
 exit:
 	mutex_unlock(&dev->io_mutex);
 	return rv;
 }

 static void skel_write_bulk_callback(struct urb *urb)
 {
 	struct usb_skel *dev;
 	unsigned long flags;

 	dev = urb->context;

 	/* sync/async unlink faults aren't errors */
 	if (urb->status) {
 		if (!(urb->status == -ENOENT ||
 		    urb->status == -ECONNRESET ||
 		    urb->status == -ESHUTDOWN))
 			dev_err(&dev->interface->dev,
 				"%s - nonzero write bulk status received: %d\n",
 				__func__, urb->status);

 		spin_lock_irqsave(&dev->err_lock, flags);
 		dev->errors = urb->status;
 		spin_unlock_irqrestore(&dev->err_lock, flags);
 	}

 	/* free up our allocated buffer */
 	usb_free_coherent(urb->dev, urb->transfer_buffer_length,
 			  urb->transfer_buffer, urb->transfer_dma);
 	up(&dev->limit_sem);
 }

 static ssize_t skel_write(struct file *file, const char *user_buffer,
 			  size_t count, loff_t *ppos)
 {
 	struct usb_skel *dev;
 	int retval = 0;
 	struct urb *urb = NULL;
 	char *buf = NULL;
 	size_t writesize = min(count, (size_t)MAX_TRANSFER);

 	dev = file->private_data;

 	/* verify that we actually have some data to write */
 	if (count == 0)
 		goto exit;

 	/*
 	 * limit the number of URBs in flight to stop a user from using up all
 	 * RAM
 	 */
 	if (!(file->f_flags & O_NONBLOCK)) {
 		if (down_interruptible(&dev->limit_sem)) {
 			retval = -ERESTARTSYS;
 			goto exit;
 		}
 	} else {
 		if (down_trylock(&dev->limit_sem)) {
 			retval = -EAGAIN;
 			goto exit;
 		}
 	}

 	spin_lock_irq(&dev->err_lock);
 	retval = dev->errors;
 	if (retval < 0) {
 		/* any error is reported once */
 		dev->errors = 0;
 		/* to preserve notifications about reset */
 		retval = (retval == -EPIPE) ? retval : -EIO;
 	}
 	spin_unlock_irq(&dev->err_lock);
 	if (retval < 0)
 		goto error;

 	/* create a urb, and a buffer for it, and copy the data to the urb */
 	urb = usb_alloc_urb(0, GFP_KERNEL);
 	if (!urb) {
 		retval = -ENOMEM;
 		goto error;
 	}

 	buf = usb_alloc_coherent(dev->udev, writesize, GFP_KERNEL,
 				 &urb->transfer_dma);
 	if (!buf) {
 		retval = -ENOMEM;
 		goto error;
 	}

 	if (copy_from_user(buf, user_buffer, writesize)) {
 		retval = -EFAULT;
 		goto error;
 	}

 	/* this lock makes sure we don't submit URBs to gone devices */
 	mutex_lock(&dev->io_mutex);
 	if (!dev->interface) {		/* disconnect() was called */
 		mutex_unlock(&dev->io_mutex);
 		retval = -ENODEV;
 		goto error;
 	}

 	/* initialize the urb properly */
 	usb_fill_bulk_urb(urb, dev->udev,
 			  usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
 			  buf, writesize, skel_write_bulk_callback, dev);
 	urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
 	usb_anchor_urb(urb, &dev->submitted);

 	/* send the data out the bulk port */
 	retval = usb_submit_urb(urb, GFP_KERNEL);
 	mutex_unlock(&dev->io_mutex);
 	if (retval) {
 		dev_err(&dev->interface->dev,
 			"%s - failed submitting write urb, error %d\n",
 			__func__, retval);
 		goto error_unanchor;
 	}

 	/*
 	 * release our reference to this urb, the USB core will eventually free
 	 * it entirely
 	 */
 	usb_free_urb(urb);


 	return writesize;

 error_unanchor:
 	usb_unanchor_urb(urb);
 error:
 	if (urb) {
 		usb_free_coherent(dev->udev, writesize, buf, urb->transfer_dma);
 		usb_free_urb(urb);
 	}
 	up(&dev->limit_sem);

 exit:
 	return retval;
 }

 static const struct file_operations skel_fops = {
 	.owner =	THIS_MODULE,
 	.read =		skel_read,
 	.write =	skel_write,
 	.open =		skel_open,
 	.release =	skel_release,
 	.flush =	skel_flush,
 	.llseek =	noop_llseek,
 };

 /*
  * usb class driver info in order to get a minor number from the usb core,
  * and to have the device registered with the driver core
  */
 static struct usb_class_driver skel_class = {
 	.name =		"skel%d",
 	.fops =		&skel_fops,
 	.minor_base =	USB_SKEL_MINOR_BASE,
 };

 static int skel_probe(struct usb_interface *interface,
 		      const struct usb_device_id *id)
 {
 	struct usb_skel *dev;
 	struct usb_endpoint_descriptor *bulk_in, *bulk_out;
 	int retval;

 	/* allocate memory for our device state and initialize it */
 	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
 	if (!dev)
 		return -ENOMEM;

 	kref_init(&dev->kref);
 	sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);
 	mutex_init(&dev->io_mutex);
 	spin_lock_init(&dev->err_lock);
 	init_usb_anchor(&dev->submitted);
 	init_waitqueue_head(&dev->bulk_in_wait);

 	dev->udev = usb_get_dev(interface_to_usbdev(interface));
 	dev->interface = interface;

 	/* set up the endpoint information */
 	/* use only the first bulk-in and bulk-out endpoints */
 	retval = usb_find_common_endpoints(interface->cur_altsetting,
 			&bulk_in, &bulk_out, NULL, NULL);
 	if (retval) {
 		dev_err(&interface->dev,
 			"Could not find both bulk-in and bulk-out endpoints\n");
 		goto error;
 	}

 	dev->bulk_in_size = usb_endpoint_maxp(bulk_in);
 	dev->bulk_in_endpointAddr = bulk_in->bEndpointAddress;
 	dev->bulk_in_buffer = kmalloc(dev->bulk_in_size, GFP_KERNEL);
 	if (!dev->bulk_in_buffer) {
 		retval = -ENOMEM;
 		goto error;
 	}
 	dev->bulk_in_urb = usb_alloc_urb(0, GFP_KERNEL);
 	if (!dev->bulk_in_urb) {
 		retval = -ENOMEM;
 		goto error;
 	}

 	dev->bulk_out_endpointAddr = bulk_out->bEndpointAddress;

 	/* save our data pointer in this interface device */
 	usb_set_intfdata(interface, dev);

 	/* we can register the device now, as it is ready */
 	retval = usb_register_dev(interface, &skel_class);
 	if (retval) {
 		/* something prevented us from registering this driver */
 		dev_err(&interface->dev,
 			"Not able to get a minor for this device.\n");
 		usb_set_intfdata(interface, NULL);
 		goto error;
 	}

 	/* let the user know what node this device is now attached to */
 	dev_info(&interface->dev,
 		 "USB Skeleton device now attached to USBSkel-%d",
 		 interface->minor);
 	return 0;

 error:
 	/* this frees allocated memory */
 	kref_put(&dev->kref, skel_delete);

 	return retval;
 }

 static void skel_disconnect(struct usb_interface *interface)
 {
 	struct usb_skel *dev;
 	int minor = interface->minor;

 	dev = usb_get_intfdata(interface);
 	usb_set_intfdata(interface, NULL);

 	/* give back our minor */
 	usb_deregister_dev(interface, &skel_class);

 	/* prevent more I/O from starting */
 	mutex_lock(&dev->io_mutex);
 	dev->interface = NULL;
 	mutex_unlock(&dev->io_mutex);

 	usb_kill_anchored_urbs(&dev->submitted);

 	/* decrement our usage count */
 	kref_put(&dev->kref, skel_delete);

 	dev_info(&interface->dev, "USB Skeleton #%d now disconnected", minor);
 }

 static void skel_draw_down(struct usb_skel *dev)
 {
 	int time;

 	time = usb_wait_anchor_empty_timeout(&dev->submitted, 1000);
 	if (!time)
 		usb_kill_anchored_urbs(&dev->submitted);
 	usb_kill_urb(dev->bulk_in_urb);
 }

 static int skel_suspend(struct usb_interface *intf, pm_message_t message)
 {
 	struct usb_skel *dev = usb_get_intfdata(intf);

 	if (!dev)
 		return 0;
 	skel_draw_down(dev);
 	return 0;
 }

 static int skel_resume(struct usb_interface *intf)
 {
 	return 0;
 }

 static int skel_pre_reset(struct usb_interface *intf)
 {
 	struct usb_skel *dev = usb_get_intfdata(intf);

 	mutex_lock(&dev->io_mutex);
 	skel_draw_down(dev);

 	return 0;
 }

 static int skel_post_reset(struct usb_interface *intf)
 {
 	struct usb_skel *dev = usb_get_intfdata(intf);

 	/* we are sure no URBs are active - no locking needed */
 	dev->errors = -EPIPE;
 	mutex_unlock(&dev->io_mutex);

 	return 0;
 }

 static struct usb_driver skel_driver = {
 	.name =		"skeleton",
 	.probe =	skel_probe,
 	.disconnect =	skel_disconnect,
 	.suspend =	skel_suspend,
 	.resume =	skel_resume,
 	.pre_reset =	skel_pre_reset,
 	.post_reset =	skel_post_reset,
 	.id_table =	skel_table,
 	.supports_autosuspend = 1,
 };

 module_usb_driver(skel_driver);

 MODULE_LICENSE("GPL v2");
	// SPDX-License-Identifier: GPL-2.0
	/*
	* USB Skeleton driver - 2.2
	*
	* Copyright (C) 2001-2004 Greg Kroah-Hartman (greg@kroah.com)
	*
	* This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c
	* but has been rewritten to be easier to read and use.
	*/

	#include <linux/kernel.h>
	#include <linux/errno.h>
	#include <linux/slab.h>
	#include <linux/module.h>
	#include <linux/kref.h>
	#include <linux/uaccess.h>
	#include <linux/usb.h>
	#include <linux/mutex.h>


	/* Define these values to match your devices */
	#define USB_SKEL_VENDOR_ID 0xfff0
	#define USB_SKEL_PRODUCT_ID 0xfff0

	/* table of devices that work with this driver */
	static const struct usb_device_id skel_table[] = {
	{ USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
	{ } /* Terminating entry */
	};
	MODULE_DEVICE_TABLE(usb, skel_table);


	/* Get a minor range for your devices from the usb maintainer */
	#define USB_SKEL_MINOR_BASE 192

	/* our private defines. if this grows any larger, use your own .h file */
	#define MAX_TRANSFER (PAGE_SIZE - 512)
	/* MAX_TRANSFER is chosen so that the VM is not stressed by
	allocations > PAGE_SIZE and the number of packets in a page
	is an integer 512 is the largest possible packet on EHCI */
	#define WRITES_IN_FLIGHT 8
	/* arbitrarily chosen */

	/* Structure to hold all of our device specific stuff */
	struct usb_skel {
	struct usb_device udev; / the usb device for this device */
	struct usb_interface interface; / the interface for this device */
	struct semaphore limit_sem; /* limiting the number of writes in progress */
	struct usb_anchor submitted; /* in case we need to retract our submissions */
	struct urb bulk_in_urb; / the urb to read data with */
	unsigned char bulk_in_buffer; / the buffer to receive data */
	size_t bulk_in_size; /* the size of the receive buffer */
	size_t bulk_in_filled; /* number of bytes in the buffer */
	size_t bulk_in_copied; /* already copied to user space */
	__u8 bulk_in_endpointAddr; /* the address of the bulk in endpoint */
	__u8 bulk_out_endpointAddr; /* the address of the bulk out endpoint */
	int errors; /* the last request tanked */
	bool ongoing_read; /* a read is going on */
	spinlock_t err_lock; /* lock for errors */
	struct kref kref;
	struct mutex io_mutex; /* synchronize I/O with disconnect */
	wait_queue_head_t bulk_in_wait; /* to wait for an ongoing read */
	};
	#define to_skel_dev(d) container_of(d, struct usb_skel, kref)

	static struct usb_driver skel_driver;
	static void skel_draw_down(struct usb_skel *dev);

	static void skel_delete(struct kref *kref)
	{
	struct usb_skel *dev = to_skel_dev(kref);

	usb_free_urb(dev->bulk_in_urb);
	usb_put_dev(dev->udev);
	kfree(dev->bulk_in_buffer);
	kfree(dev);
	}

	static int skel_open(struct inode inode, struct file file)
	{
	struct usb_skel *dev;
	struct usb_interface *interface;
	int subminor;
	int retval = 0;

	subminor = iminor(inode);

	interface = usb_find_interface(&skel_driver, subminor);
	if (!interface) {
	pr_err("%s - error, can't find device for minor %d\n",
	__func__, subminor);
	retval = -ENODEV;
	goto exit;
	}

	dev = usb_get_intfdata(interface);
	if (!dev) {
	retval = -ENODEV;
	goto exit;
	}

	retval = usb_autopm_get_interface(interface);
	if (retval)
	goto exit;

	/* increment our usage count for the device */
	kref_get(&dev->kref);

	/* save our object in the file's private structure */
	file->private_data = dev;

	exit:
	return retval;
	}

	static int skel_release(struct inode inode, struct file file)
	{
	struct usb_skel *dev;

	dev = file->private_data;
	if (dev == NULL)
	return -ENODEV;

	/* allow the device to be autosuspended */
	mutex_lock(&dev->io_mutex);
	if (dev->interface)
	usb_autopm_put_interface(dev->interface);
	mutex_unlock(&dev->io_mutex);

	/* decrement the count on our device */
	kref_put(&dev->kref, skel_delete);
	return 0;
	}

	static int skel_flush(struct file *file, fl_owner_t id)
	{
	struct usb_skel *dev;
	int res;

	dev = file->private_data;
	if (dev == NULL)
	return -ENODEV;

	/* wait for io to stop */
	mutex_lock(&dev->io_mutex);
	skel_draw_down(dev);

	/* read out errors, leave subsequent opens a clean slate */
	spin_lock_irq(&dev->err_lock);
	res = dev->errors ? (dev->errors == -EPIPE ? -EPIPE : -EIO) : 0;
	dev->errors = 0;
	spin_unlock_irq(&dev->err_lock);

	mutex_unlock(&dev->io_mutex);

	return res;
	}

	static void skel_read_bulk_callback(struct urb *urb)
	{
	struct usb_skel *dev;
	unsigned long flags;

	dev = urb->context;

	spin_lock_irqsave(&dev->err_lock, flags);
	/* sync/async unlink faults aren't errors */
	if (urb->status) {
	if (!(urb->status == -ENOENT \|\|
	urb->status == -ECONNRESET \|\|
	urb->status == -ESHUTDOWN))
	dev_err(&dev->interface->dev,
	"%s - nonzero write bulk status received: %d\n",
	__func__, urb->status);

	dev->errors = urb->status;
	} else {
	dev->bulk_in_filled = urb->actual_length;
	}
	dev->ongoing_read = 0;
	spin_unlock_irqrestore(&dev->err_lock, flags);

	wake_up_interruptible(&dev->bulk_in_wait);
	}

	static int skel_do_read_io(struct usb_skel *dev, size_t count)
	{
	int rv;

	/* prepare a read */
	usb_fill_bulk_urb(dev->bulk_in_urb,
	dev->udev,
	usb_rcvbulkpipe(dev->udev,
	dev->bulk_in_endpointAddr),
	dev->bulk_in_buffer,
	min(dev->bulk_in_size, count),
	skel_read_bulk_callback,
	dev);
	/* tell everybody to leave the URB alone */
	spin_lock_irq(&dev->err_lock);
	dev->ongoing_read = 1;
	spin_unlock_irq(&dev->err_lock);

	/* submit bulk in urb, which means no data to deliver */
	dev->bulk_in_filled = 0;
	dev->bulk_in_copied = 0;

	/* do it */
	rv = usb_submit_urb(dev->bulk_in_urb, GFP_KERNEL);
	if (rv < 0) {
	dev_err(&dev->interface->dev,
	"%s - failed submitting read urb, error %d\n",
	__func__, rv);
	rv = (rv == -ENOMEM) ? rv : -EIO;
	spin_lock_irq(&dev->err_lock);
	dev->ongoing_read = 0;
	spin_unlock_irq(&dev->err_lock);
	}

	return rv;
	}

	static ssize_t skel_read(struct file file, char buffer, size_t count,
	loff_t *ppos)
	{
	struct usb_skel *dev;
	int rv;
	bool ongoing_io;

	dev = file->private_data;

	/* if we cannot read at all, return EOF */
	if (!dev->bulk_in_urb \|\| !count)
	return 0;

	/* no concurrent readers */
	rv = mutex_lock_interruptible(&dev->io_mutex);
	if (rv < 0)
	return rv;

	if (!dev->interface) { /* disconnect() was called */
	rv = -ENODEV;
	goto exit;
	}

	/* if IO is under way, we must not touch things */
	retry:
	spin_lock_irq(&dev->err_lock);
	ongoing_io = dev->ongoing_read;
	spin_unlock_irq(&dev->err_lock);

	if (ongoing_io) {
	/* nonblocking IO shall not wait */
	if (file->f_flags & O_NONBLOCK) {
	rv = -EAGAIN;
	goto exit;
	}
	/*
	* IO may take forever
	* hence wait in an interruptible state
	*/
	rv = wait_event_interruptible(dev->bulk_in_wait, (!dev->ongoing_read));
	if (rv < 0)
	goto exit;
	}

	/* errors must be reported */
	rv = dev->errors;
	if (rv < 0) {
	/* any error is reported once */
	dev->errors = 0;
	/* to preserve notifications about reset */
	rv = (rv == -EPIPE) ? rv : -EIO;
	/* report it */
	goto exit;
	}

	/*
	* if the buffer is filled we may satisfy the read
	* else we need to start IO
	*/

	if (dev->bulk_in_filled) {
	/* we had read data */
	size_t available = dev->bulk_in_filled - dev->bulk_in_copied;
	size_t chunk = min(available, count);

	if (!available) {
	/*
	* all data has been used
	* actual IO needs to be done
	*/
	rv = skel_do_read_io(dev, count);
	if (rv < 0)
	goto exit;
	else
	goto retry;
	}
	/*
	* data is available
	* chunk tells us how much shall be copied
	*/

	if (copy_to_user(buffer,
	dev->bulk_in_buffer + dev->bulk_in_copied,
	chunk))
	rv = -EFAULT;
	else
	rv = chunk;

	dev->bulk_in_copied += chunk;

	/*
	* if we are asked for more than we have,
	* we start IO but don't wait
	*/
	if (available < count)
	skel_do_read_io(dev, count - chunk);
	} else {
	/* no data in the buffer */
	rv = skel_do_read_io(dev, count);
	if (rv < 0)
	goto exit;
	else
	goto retry;
	}
	exit:
	mutex_unlock(&dev->io_mutex);
	return rv;
	}

	static void skel_write_bulk_callback(struct urb *urb)
	{
	struct usb_skel *dev;
	unsigned long flags;

	dev = urb->context;

	/* sync/async unlink faults aren't errors */
	if (urb->status) {
	if (!(urb->status == -ENOENT \|\|
	urb->status == -ECONNRESET \|\|
	urb->status == -ESHUTDOWN))
	dev_err(&dev->interface->dev,
	"%s - nonzero write bulk status received: %d\n",
	__func__, urb->status);

	spin_lock_irqsave(&dev->err_lock, flags);
	dev->errors = urb->status;
	spin_unlock_irqrestore(&dev->err_lock, flags);
	}

	/* free up our allocated buffer */
	usb_free_coherent(urb->dev, urb->transfer_buffer_length,
	urb->transfer_buffer, urb->transfer_dma);
	up(&dev->limit_sem);
	}

	static ssize_t skel_write(struct file file, const char user_buffer,
	size_t count, loff_t *ppos)
	{
	struct usb_skel *dev;
	int retval = 0;
	struct urb *urb = NULL;
	char *buf = NULL;
	size_t writesize = min(count, (size_t)MAX_TRANSFER);

	dev = file->private_data;

	/* verify that we actually have some data to write */
	if (count == 0)
	goto exit;

	/*
	* limit the number of URBs in flight to stop a user from using up all
	* RAM
	*/
	if (!(file->f_flags & O_NONBLOCK)) {
	if (down_interruptible(&dev->limit_sem)) {
	retval = -ERESTARTSYS;
	goto exit;
	}
	} else {
	if (down_trylock(&dev->limit_sem)) {
	retval = -EAGAIN;
	goto exit;
	}
	}

	spin_lock_irq(&dev->err_lock);
	retval = dev->errors;
	if (retval < 0) {
	/* any error is reported once */
	dev->errors = 0;
	/* to preserve notifications about reset */
	retval = (retval == -EPIPE) ? retval : -EIO;
	}
	spin_unlock_irq(&dev->err_lock);
	if (retval < 0)
	goto error;

	/* create a urb, and a buffer for it, and copy the data to the urb */
	urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!urb) {
	retval = -ENOMEM;
	goto error;
	}

	buf = usb_alloc_coherent(dev->udev, writesize, GFP_KERNEL,
	&urb->transfer_dma);
	if (!buf) {
	retval = -ENOMEM;
	goto error;
	}

	if (copy_from_user(buf, user_buffer, writesize)) {
	retval = -EFAULT;
	goto error;
	}

	/* this lock makes sure we don't submit URBs to gone devices */
	mutex_lock(&dev->io_mutex);
	if (!dev->interface) { /* disconnect() was called */
	mutex_unlock(&dev->io_mutex);
	retval = -ENODEV;
	goto error;
	}

	/* initialize the urb properly */
	usb_fill_bulk_urb(urb, dev->udev,
	usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
	buf, writesize, skel_write_bulk_callback, dev);
	urb->transfer_flags \|= URB_NO_TRANSFER_DMA_MAP;
	usb_anchor_urb(urb, &dev->submitted);

	/* send the data out the bulk port */
	retval = usb_submit_urb(urb, GFP_KERNEL);
	mutex_unlock(&dev->io_mutex);
	if (retval) {
	dev_err(&dev->interface->dev,
	"%s - failed submitting write urb, error %d\n",
	__func__, retval);
	goto error_unanchor;
	}

	/*
	* release our reference to this urb, the USB core will eventually free
	* it entirely
	*/
	usb_free_urb(urb);


	return writesize;

	error_unanchor:
	usb_unanchor_urb(urb);
	error:
	if (urb) {
	usb_free_coherent(dev->udev, writesize, buf, urb->transfer_dma);
	usb_free_urb(urb);
	}
	up(&dev->limit_sem);

	exit:
	return retval;
	}

	static const struct file_operations skel_fops = {
	.owner = THIS_MODULE,
	.read = skel_read,
	.write = skel_write,
	.open = skel_open,
	.release = skel_release,
	.flush = skel_flush,
	.llseek = noop_llseek,
	};

	/*
	* usb class driver info in order to get a minor number from the usb core,
	* and to have the device registered with the driver core
	*/
	static struct usb_class_driver skel_class = {
	.name = "skel%d",
	.fops = &skel_fops,
	.minor_base = USB_SKEL_MINOR_BASE,
	};

	static int skel_probe(struct usb_interface *interface,
	const struct usb_device_id *id)
	{
	struct usb_skel *dev;
	struct usb_endpoint_descriptor bulk_in, bulk_out;
	int retval;

	/* allocate memory for our device state and initialize it */
	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (!dev)
	return -ENOMEM;

	kref_init(&dev->kref);
	sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);
	mutex_init(&dev->io_mutex);
	spin_lock_init(&dev->err_lock);
	init_usb_anchor(&dev->submitted);
	init_waitqueue_head(&dev->bulk_in_wait);

	dev->udev = usb_get_dev(interface_to_usbdev(interface));
	dev->interface = interface;

	/* set up the endpoint information */
	/* use only the first bulk-in and bulk-out endpoints */
	retval = usb_find_common_endpoints(interface->cur_altsetting,
	&bulk_in, &bulk_out, NULL, NULL);
	if (retval) {
	dev_err(&interface->dev,
	"Could not find both bulk-in and bulk-out endpoints\n");
	goto error;
	}

	dev->bulk_in_size = usb_endpoint_maxp(bulk_in);
	dev->bulk_in_endpointAddr = bulk_in->bEndpointAddress;
	dev->bulk_in_buffer = kmalloc(dev->bulk_in_size, GFP_KERNEL);
	if (!dev->bulk_in_buffer) {
	retval = -ENOMEM;
	goto error;
	}
	dev->bulk_in_urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!dev->bulk_in_urb) {
	retval = -ENOMEM;
	goto error;
	}

	dev->bulk_out_endpointAddr = bulk_out->bEndpointAddress;

	/* save our data pointer in this interface device */
	usb_set_intfdata(interface, dev);

	/* we can register the device now, as it is ready */
	retval = usb_register_dev(interface, &skel_class);
	if (retval) {
	/* something prevented us from registering this driver */
	dev_err(&interface->dev,
	"Not able to get a minor for this device.\n");
	usb_set_intfdata(interface, NULL);
	goto error;
	}

	/* let the user know what node this device is now attached to */
	dev_info(&interface->dev,
	"USB Skeleton device now attached to USBSkel-%d",
	interface->minor);
	return 0;

	error:
	/* this frees allocated memory */
	kref_put(&dev->kref, skel_delete);

	return retval;
	}

	static void skel_disconnect(struct usb_interface *interface)
	{
	struct usb_skel *dev;
	int minor = interface->minor;

	dev = usb_get_intfdata(interface);
	usb_set_intfdata(interface, NULL);

	/* give back our minor */
	usb_deregister_dev(interface, &skel_class);

	/* prevent more I/O from starting */
	mutex_lock(&dev->io_mutex);
	dev->interface = NULL;
	mutex_unlock(&dev->io_mutex);

	usb_kill_anchored_urbs(&dev->submitted);

	/* decrement our usage count */
	kref_put(&dev->kref, skel_delete);

	dev_info(&interface->dev, "USB Skeleton #%d now disconnected", minor);
	}

	static void skel_draw_down(struct usb_skel *dev)
	{
	int time;

	time = usb_wait_anchor_empty_timeout(&dev->submitted, 1000);
	if (!time)
	usb_kill_anchored_urbs(&dev->submitted);
	usb_kill_urb(dev->bulk_in_urb);
	}

	static int skel_suspend(struct usb_interface *intf, pm_message_t message)
	{
	struct usb_skel *dev = usb_get_intfdata(intf);

	if (!dev)
	return 0;
	skel_draw_down(dev);
	return 0;
	}

	static int skel_resume(struct usb_interface *intf)
	{
	return 0;
	}

	static int skel_pre_reset(struct usb_interface *intf)
	{
	struct usb_skel *dev = usb_get_intfdata(intf);

	mutex_lock(&dev->io_mutex);
	skel_draw_down(dev);

	return 0;
	}

	static int skel_post_reset(struct usb_interface *intf)
	{
	struct usb_skel *dev = usb_get_intfdata(intf);

	/* we are sure no URBs are active - no locking needed */
	dev->errors = -EPIPE;
	mutex_unlock(&dev->io_mutex);

	return 0;
	}

	static struct usb_driver skel_driver = {
	.name = "skeleton",
	.probe = skel_probe,
	.disconnect = skel_disconnect,
	.suspend = skel_suspend,
	.resume = skel_resume,
	.pre_reset = skel_pre_reset,
	.post_reset = skel_post_reset,
	.id_table = skel_table,
	.supports_autosuspend = 1,
	};

	module_usb_driver(skel_driver);

	MODULE_LICENSE("GPL v2");