drivers/usb/usb-skeleton.c

   1 /*
   2  * USB Skeleton driver - 2.2
   3  *
   4  * Copyright (C) 2001-2004 Greg Kroah-Hartman (greg@kroah.com)
   5  *
   6  *      This program is free software; you can redistribute it and/or
   7  *      modify it under the terms of the GNU General Public License as
   8  *      published by the Free Software Foundation, version 2.
   9  *
  10  * This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c
  11  * but has been rewritten to be easier to read and use.
  12  *
  13  */
  14
  15 #include <linux/kernel.h>
  16 #include <linux/errno.h>
  17 #include <linux/init.h>
  18 #include <linux/slab.h>
  19 #include <linux/module.h>
  20 #include <linux/kref.h>
  21 #include <linux/smp_lock.h>
  22 #include <linux/uaccess.h>
  23 #include <linux/usb.h>
  24 #include <linux/mutex.h>
  25
  26
  27 /* Define these values to match your devices */
  28 #define USB_SKEL_VENDOR_ID      0xfff0
  29 #define USB_SKEL_PRODUCT_ID     0xfff0
  30
  31 /* table of devices that work with this driver */
  32 static const struct usb_device_id skel_table[] = {
  33         { USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
  34         { }                                     /* Terminating entry */
  35 };
  36 MODULE_DEVICE_TABLE(usb, skel_table);
  37
  38
  39 /* Get a minor range for your devices from the usb maintainer */
  40 #define USB_SKEL_MINOR_BASE     192
  41
  42 /* our private defines. if this grows any larger, use your own .h file */
  43 #define MAX_TRANSFER            (PAGE_SIZE - 512)
  44 /* MAX_TRANSFER is chosen so that the VM is not stressed by
  45    allocations > PAGE_SIZE and the number of packets in a page
  46    is an integer 512 is the largest possible packet on EHCI */
  47 #define WRITES_IN_FLIGHT        8
  48 /* arbitrarily chosen */
  49
  50 /* Structure to hold all of our device specific stuff */
  51 struct usb_skel {
  52         struct usb_device       *udev;                  /* the usb device for this device */
  53         struct usb_interface    *interface;             /* the interface for this device */
  54         struct semaphore        limit_sem;              /* limiting the number of writes in progress */
  55         struct usb_anchor       submitted;              /* in case we need to retract our submissions */
  56         struct urb              *bulk_in_urb;           /* the urb to read data with */
  57         unsigned char           *bulk_in_buffer;        /* the buffer to receive data */
  58         size_t                  bulk_in_size;           /* the size of the receive buffer */
  59         size_t                  bulk_in_filled;         /* number of bytes in the buffer */
  60         size_t                  bulk_in_copied;         /* already copied to user space */
  61         __u8                    bulk_in_endpointAddr;   /* the address of the bulk in endpoint */
  62         __u8                    bulk_out_endpointAddr;  /* the address of the bulk out endpoint */
  63         int                     errors;                 /* the last request tanked */
  64         int                     open_count;             /* count the number of openers */
  65         bool                    ongoing_read;           /* a read is going on */
  66         bool                    processed_urb;          /* indicates we haven't processed the urb */
  67         spinlock_t              err_lock;               /* lock for errors */
  68         struct kref             kref;
  69         struct mutex            io_mutex;               /* synchronize I/O with disconnect */
  70         struct completion       bulk_in_completion;     /* to wait for an ongoing read */
  71 };
  72 #define to_skel_dev(d) container_of(d, struct usb_skel, kref)
  73
  74 static struct usb_driver skel_driver;
  75 static void skel_draw_down(struct usb_skel *dev);
  76
  77 static void skel_delete(struct kref *kref)
  78 {
  79         struct usb_skel *dev = to_skel_dev(kref);
  80
  81         usb_free_urb(dev->bulk_in_urb);
  82         usb_put_dev(dev->udev);
  83         kfree(dev->bulk_in_buffer);
  84         kfree(dev);
  85 }
  86
  87 static int skel_open(struct inode *inode, struct file *file)
  88 {
  89         struct usb_skel *dev;
  90         struct usb_interface *interface;
  91         int subminor;
  92         int retval = 0;
  93
  94         lock_kernel();
  95         subminor = iminor(inode);
  96
  97         interface = usb_find_interface(&skel_driver, subminor);
  98         if (!interface) {
  99                 err("%s - error, can't find device for minor %d",
 100                      __func__, subminor);
 101                 retval = -ENODEV;
 102                 goto exit;
 103         }
 104
 105         dev = usb_get_intfdata(interface);
 106         if (!dev) {
 107                 retval = -ENODEV;
 108                 goto exit;
 109         }
 110
 111         /* increment our usage count for the device */
 112         kref_get(&dev->kref);
 113
 114         /* lock the device to allow correctly handling errors
 115          * in resumption */
 116         mutex_lock(&dev->io_mutex);
 117
 118         if (!dev->open_count++) {
 119                 retval = usb_autopm_get_interface(interface);
 120                         if (retval) {
 121                                 dev->open_count--;
 122                                 mutex_unlock(&dev->io_mutex);
 123                                 kref_put(&dev->kref, skel_delete);
 124                                 goto exit;
 125                         }
 126         } /* else { //uncomment this block if you want exclusive open
 127                 retval = -EBUSY;
 128                 dev->open_count--;
 129                 mutex_unlock(&dev->io_mutex);
 130                 kref_put(&dev->kref, skel_delete);
 131                 goto exit;
 132         } */
 133         /* prevent the device from being autosuspended */
 134
 135         /* save our object in the file's private structure */
 136         file->private_data = dev;
 137         mutex_unlock(&dev->io_mutex);
 138
 139 exit:
 140         unlock_kernel();
 141         return retval;
 142 }
 143
 144 static int skel_release(struct inode *inode, struct file *file)
 145 {
 146         struct usb_skel *dev;
 147
 148         dev = (struct usb_skel *)file->private_data;
 149         if (dev == NULL)
 150                 return -ENODEV;
 151
 152         /* allow the device to be autosuspended */
 153         mutex_lock(&dev->io_mutex);
 154         if (!--dev->open_count && dev->interface)
 155                 usb_autopm_put_interface(dev->interface);
 156         mutex_unlock(&dev->io_mutex);
 157
 158         /* decrement the count on our device */
 159         kref_put(&dev->kref, skel_delete);
 160         return 0;
 161 }
 162
 163 static int skel_flush(struct file *file, fl_owner_t id)
 164 {
 165         struct usb_skel *dev;
 166         int res;
 167
 168         dev = (struct usb_skel *)file->private_data;
 169         if (dev == NULL)
 170                 return -ENODEV;
 171
 172         /* wait for io to stop */
 173         mutex_lock(&dev->io_mutex);
 174         skel_draw_down(dev);
 175
 176         /* read out errors, leave subsequent opens a clean slate */
 177         spin_lock_irq(&dev->err_lock);
 178         res = dev->errors ? (dev->errors == -EPIPE ? -EPIPE : -EIO) : 0;
 179         dev->errors = 0;
 180         spin_unlock_irq(&dev->err_lock);
 181
 182         mutex_unlock(&dev->io_mutex);
 183
 184         return res;
 185 }
 186
 187 static void skel_read_bulk_callback(struct urb *urb)
 188 {
 189         struct usb_skel *dev;
 190
 191         dev = urb->context;
 192
 193         spin_lock(&dev->err_lock);
 194         /* sync/async unlink faults aren't errors */
 195         if (urb->status) {
 196                 if (!(urb->status == -ENOENT ||
 197                     urb->status == -ECONNRESET ||
 198                     urb->status == -ESHUTDOWN))
 199                         err("%s - nonzero write bulk status received: %d",
 200                             __func__, urb->status);
 201
 202                 dev->errors = urb->status;
 203         } else {
 204                 dev->bulk_in_filled = urb->actual_length;
 205         }
 206         dev->ongoing_read = 0;
 207         spin_unlock(&dev->err_lock);
 208
 209         complete(&dev->bulk_in_completion);
 210 }
 211
 212 static int skel_do_read_io(struct usb_skel *dev, size_t count)
 213 {
 214         int rv;
 215
 216         /* prepare a read */
 217         usb_fill_bulk_urb(dev->bulk_in_urb,
 218                         dev->udev,
 219                         usb_rcvbulkpipe(dev->udev,
 220                                 dev->bulk_in_endpointAddr),
 221                         dev->bulk_in_buffer,
 222                         min(dev->bulk_in_size, count),
 223                         skel_read_bulk_callback,
 224                         dev);
 225         /* tell everybody to leave the URB alone */
 226         spin_lock_irq(&dev->err_lock);
 227         dev->ongoing_read = 1;
 228         spin_unlock_irq(&dev->err_lock);
 229
 230         /* do it */
 231         rv = usb_submit_urb(dev->bulk_in_urb, GFP_KERNEL);
 232         if (rv < 0) {
 233                 err("%s - failed submitting read urb, error %d",
 234                         __func__, rv);
 235                 dev->bulk_in_filled = 0;
 236                 rv = (rv == -ENOMEM) ? rv : -EIO;
 237                 spin_lock_irq(&dev->err_lock);
 238                 dev->ongoing_read = 0;
 239                 spin_unlock_irq(&dev->err_lock);
 240         }
 241
 242         return rv;
 243 }
 244
 245 static ssize_t skel_read(struct file *file, char *buffer, size_t count,
 246                          loff_t *ppos)
 247 {
 248         struct usb_skel *dev;
 249         int rv;
 250         bool ongoing_io;
 251
 252         dev = (struct usb_skel *)file->private_data;
 253
 254         /* if we cannot read at all, return EOF */
 255         if (!dev->bulk_in_urb || !count)
 256                 return 0;
 257
 258         /* no concurrent readers */
 259         rv = mutex_lock_interruptible(&dev->io_mutex);
 260         if (rv < 0)
 261                 return rv;
 262
 263         if (!dev->interface) {          /* disconnect() was called */
 264                 rv = -ENODEV;
 265                 goto exit;
 266         }
 267
 268         /* if IO is under way, we must not touch things */
 269 retry:
 270         spin_lock_irq(&dev->err_lock);
 271         ongoing_io = dev->ongoing_read;
 272         spin_unlock_irq(&dev->err_lock);
 273
 274         if (ongoing_io) {
 275                 /* nonblocking IO shall not wait */
 276                 if (file->f_flags & O_NONBLOCK) {
 277                         rv = -EAGAIN;
 278                         goto exit;
 279                 }
 280                 /*
 281                  * IO may take forever
 282                  * hence wait in an interruptible state
 283                  */
 284                 rv = wait_for_completion_interruptible(&dev->bulk_in_completion);
 285                 if (rv < 0)
 286                         goto exit;
 287                 /*
 288                  * by waiting we also semiprocessed the urb
 289                  * we must finish now
 290                  */
 291                 dev->bulk_in_copied = 0;
 292                 dev->processed_urb = 1;
 293         }
 294
 295         if (!dev->processed_urb) {
 296                 /*
 297                  * the URB hasn't been processed
 298                  * do it now
 299                  */
 300                 wait_for_completion(&dev->bulk_in_completion);
 301                 dev->bulk_in_copied = 0;
 302                 dev->processed_urb = 1;
 303         }
 304
 305         /* errors must be reported */
 306         rv = dev->errors;
 307         if (rv < 0) {
 308                 /* any error is reported once */
 309                 dev->errors = 0;
 310                 /* to preserve notifications about reset */
 311                 rv = (rv == -EPIPE) ? rv : -EIO;
 312                 /* no data to deliver */
 313                 dev->bulk_in_filled = 0;
 314                 /* report it */
 315                 goto exit;
 316         }
 317
 318         /*
 319          * if the buffer is filled we may satisfy the read
 320          * else we need to start IO
 321          */
 322
 323         if (dev->bulk_in_filled) {
 324                 /* we had read data */
 325                 size_t available = dev->bulk_in_filled - dev->bulk_in_copied;
 326                 size_t chunk = min(available, count);
 327
 328                 if (!available) {
 329                         /*
 330                          * all data has been used
 331                          * actual IO needs to be done
 332                          */
 333                         rv = skel_do_read_io(dev, count);
 334                         if (rv < 0)
 335                                 goto exit;
 336                         else
 337                                 goto retry;
 338                 }
 339                 /*
 340                  * data is available
 341                  * chunk tells us how much shall be copied
 342                  */
 343
 344                 if (copy_to_user(buffer,
 345                                  dev->bulk_in_buffer + dev->bulk_in_copied,
 346                                  chunk))
 347                         rv = -EFAULT;
 348                 else
 349                         rv = chunk;
 350
 351                 dev->bulk_in_copied += chunk;
 352
 353                 /*
 354                  * if we are asked for more than we have,
 355                  * we start IO but don't wait
 356                  */
 357                 if (available < count)
 358                         skel_do_read_io(dev, count - chunk);
 359         } else {
 360                 /* no data in the buffer */
 361                 rv = skel_do_read_io(dev, count);
 362                 if (rv < 0)
 363                         goto exit;
 364                 else if (!(file->f_flags & O_NONBLOCK))
 365                         goto retry;
 366                 rv = -EAGAIN;
 367         }
 368 exit:
 369         mutex_unlock(&dev->io_mutex);
 370         return rv;
 371 }
 372
 373 static void skel_write_bulk_callback(struct urb *urb)
 374 {
 375         struct usb_skel *dev;
 376
 377         dev = urb->context;
 378
 379         /* sync/async unlink faults aren't errors */
 380         if (urb->status) {
 381                 if (!(urb->status == -ENOENT ||
 382                     urb->status == -ECONNRESET ||
 383                     urb->status == -ESHUTDOWN))
 384                         err("%s - nonzero write bulk status received: %d",
 385                             __func__, urb->status);
 386
 387                 spin_lock(&dev->err_lock);
 388                 dev->errors = urb->status;
 389                 spin_unlock(&dev->err_lock);
 390         }
 391
 392         /* free up our allocated buffer */
 393         usb_buffer_free(urb->dev, urb->transfer_buffer_length,
 394                         urb->transfer_buffer, urb->transfer_dma);
 395         up(&dev->limit_sem);
 396 }
 397
 398 static ssize_t skel_write(struct file *file, const char *user_buffer,
 399                           size_t count, loff_t *ppos)
 400 {
 401         struct usb_skel *dev;
 402         int retval = 0;
 403         struct urb *urb = NULL;
 404         char *buf = NULL;
 405         size_t writesize = min(count, (size_t)MAX_TRANSFER);
 406
 407         dev = (struct usb_skel *)file->private_data;
 408
 409         /* verify that we actually have some data to write */
 410         if (count == 0)
 411                 goto exit;
 412
 413         /*
 414          * limit the number of URBs in flight to stop a user from using up all
 415          * RAM
 416          */
 417         if (!(file->f_flags & O_NONBLOCK)) {
 418                 if (down_interruptible(&dev->limit_sem)) {
 419                         retval = -ERESTARTSYS;
 420                         goto exit;
 421                 }
 422         } else {
 423                 if (down_trylock(&dev->limit_sem)) {
 424                         retval = -EAGAIN;
 425                         goto exit;
 426                 }
 427         }
 428
 429         spin_lock_irq(&dev->err_lock);
 430         retval = dev->errors;
 431         if (retval < 0) {
 432                 /* any error is reported once */
 433                 dev->errors = 0;
 434                 /* to preserve notifications about reset */
 435                 retval = (retval == -EPIPE) ? retval : -EIO;
 436         }
 437         spin_unlock_irq(&dev->err_lock);
 438         if (retval < 0)
 439                 goto error;
 440
 441         /* create a urb, and a buffer for it, and copy the data to the urb */
 442         urb = usb_alloc_urb(0, GFP_KERNEL);
 443         if (!urb) {
 444                 retval = -ENOMEM;
 445                 goto error;
 446         }
 447
 448         buf = usb_buffer_alloc(dev->udev, writesize, GFP_KERNEL,
 449                                &urb->transfer_dma);
 450         if (!buf) {
 451                 retval = -ENOMEM;
 452                 goto error;
 453         }
 454
 455         if (copy_from_user(buf, user_buffer, writesize)) {
 456                 retval = -EFAULT;
 457                 goto error;
 458         }
 459
 460         /* this lock makes sure we don't submit URBs to gone devices */
 461         mutex_lock(&dev->io_mutex);
 462         if (!dev->interface) {          /* disconnect() was called */
 463                 mutex_unlock(&dev->io_mutex);
 464                 retval = -ENODEV;
 465                 goto error;
 466         }
 467
 468         /* initialize the urb properly */
 469         usb_fill_bulk_urb(urb, dev->udev,
 470                           usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
 471                           buf, writesize, skel_write_bulk_callback, dev);
 472         urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
 473         usb_anchor_urb(urb, &dev->submitted);
 474
 475         /* send the data out the bulk port */
 476         retval = usb_submit_urb(urb, GFP_KERNEL);
 477         mutex_unlock(&dev->io_mutex);
 478         if (retval) {
 479                 err("%s - failed submitting write urb, error %d", __func__,
 480                     retval);
 481                 goto error_unanchor;
 482         }
 483
 484         /*
 485          * release our reference to this urb, the USB core will eventually free
 486          * it entirely
 487          */
 488         usb_free_urb(urb);
 489
 490
 491         return writesize;
 492
 493 error_unanchor:
 494         usb_unanchor_urb(urb);
 495 error:
 496         if (urb) {
 497                 usb_buffer_free(dev->udev, writesize, buf, urb->transfer_dma);
 498                 usb_free_urb(urb);
 499         }
 500         up(&dev->limit_sem);
 501
 502 exit:
 503         return retval;
 504 }
 505
 506 static const struct file_operations skel_fops = {
 507         .owner =        THIS_MODULE,
 508         .read =         skel_read,
 509         .write =        skel_write,
 510         .open =         skel_open,
 511         .release =      skel_release,
 512         .flush =        skel_flush,
 513 };
 514
 515 /*
 516  * usb class driver info in order to get a minor number from the usb core,
 517  * and to have the device registered with the driver core
 518  */
 519 static struct usb_class_driver skel_class = {
 520         .name =         "skel%d",
 521         .fops =         &skel_fops,
 522         .minor_base =   USB_SKEL_MINOR_BASE,
 523 };
 524
 525 static int skel_probe(struct usb_interface *interface,
 526                       const struct usb_device_id *id)
 527 {
 528         struct usb_skel *dev;
 529         struct usb_host_interface *iface_desc;
 530         struct usb_endpoint_descriptor *endpoint;
 531         size_t buffer_size;
 532         int i;
 533         int retval = -ENOMEM;
 534
 535         /* allocate memory for our device state and initialize it */
 536         dev = kzalloc(sizeof(*dev), GFP_KERNEL);
 537         if (!dev) {
 538                 err("Out of memory");
 539                 goto error;
 540         }
 541         kref_init(&dev->kref);
 542         sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);
 543         mutex_init(&dev->io_mutex);
 544         spin_lock_init(&dev->err_lock);
 545         init_usb_anchor(&dev->submitted);
 546         init_completion(&dev->bulk_in_completion);
 547
 548         dev->udev = usb_get_dev(interface_to_usbdev(interface));
 549         dev->interface = interface;
 550
 551         /* set up the endpoint information */
 552         /* use only the first bulk-in and bulk-out endpoints */
 553         iface_desc = interface->cur_altsetting;
 554         for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
 555                 endpoint = &iface_desc->endpoint[i].desc;
 556
 557                 if (!dev->bulk_in_endpointAddr &&
 558                     usb_endpoint_is_bulk_in(endpoint)) {
 559                         /* we found a bulk in endpoint */
 560                         buffer_size = le16_to_cpu(endpoint->wMaxPacketSize);
 561                         dev->bulk_in_size = buffer_size;
 562                         dev->bulk_in_endpointAddr = endpoint->bEndpointAddress;
 563                         dev->bulk_in_buffer = kmalloc(buffer_size, GFP_KERNEL);
 564                         if (!dev->bulk_in_buffer) {
 565                                 err("Could not allocate bulk_in_buffer");
 566                                 goto error;
 567                         }
 568                         dev->bulk_in_urb = usb_alloc_urb(0, GFP_KERNEL);
 569                         if (!dev->bulk_in_urb) {
 570                                 err("Could not allocate bulk_in_urb");
 571                                 goto error;
 572                         }
 573                 }
 574
 575                 if (!dev->bulk_out_endpointAddr &&
 576                     usb_endpoint_is_bulk_out(endpoint)) {
 577                         /* we found a bulk out endpoint */
 578                         dev->bulk_out_endpointAddr = endpoint->bEndpointAddress;
 579                 }
 580         }
 581         if (!(dev->bulk_in_endpointAddr && dev->bulk_out_endpointAddr)) {
 582                 err("Could not find both bulk-in and bulk-out endpoints");
 583                 goto error;
 584         }
 585
 586         /* save our data pointer in this interface device */
 587         usb_set_intfdata(interface, dev);
 588
 589         /* we can register the device now, as it is ready */
 590         retval = usb_register_dev(interface, &skel_class);
 591         if (retval) {
 592                 /* something prevented us from registering this driver */
 593                 err("Not able to get a minor for this device.");
 594                 usb_set_intfdata(interface, NULL);
 595                 goto error;
 596         }
 597
 598         /* let the user know what node this device is now attached to */
 599         dev_info(&interface->dev,
 600                  "USB Skeleton device now attached to USBSkel-%d",
 601                  interface->minor);
 602         return 0;
 603
 604 error:
 605         if (dev)
 606                 /* this frees allocated memory */
 607                 kref_put(&dev->kref, skel_delete);
 608         return retval;
 609 }
 610
 611 static void skel_disconnect(struct usb_interface *interface)
 612 {
 613         struct usb_skel *dev;
 614         int minor = interface->minor;
 615
 616         dev = usb_get_intfdata(interface);
 617         usb_set_intfdata(interface, NULL);
 618
 619         /* give back our minor */
 620         usb_deregister_dev(interface, &skel_class);
 621
 622         /* prevent more I/O from starting */
 623         mutex_lock(&dev->io_mutex);
 624         dev->interface = NULL;
 625         mutex_unlock(&dev->io_mutex);
 626
 627         usb_kill_anchored_urbs(&dev->submitted);
 628
 629         /* decrement our usage count */
 630         kref_put(&dev->kref, skel_delete);
 631
 632         dev_info(&interface->dev, "USB Skeleton #%d now disconnected", minor);
 633 }
 634
 635 static void skel_draw_down(struct usb_skel *dev)
 636 {
 637         int time;
 638
 639         time = usb_wait_anchor_empty_timeout(&dev->submitted, 1000);
 640         if (!time)
 641                 usb_kill_anchored_urbs(&dev->submitted);
 642         usb_kill_urb(dev->bulk_in_urb);
 643 }
 644
 645 static int skel_suspend(struct usb_interface *intf, pm_message_t message)
 646 {
 647         struct usb_skel *dev = usb_get_intfdata(intf);
 648
 649         if (!dev)
 650                 return 0;
 651         skel_draw_down(dev);
 652         return 0;
 653 }
 654
 655 static int skel_resume(struct usb_interface *intf)
 656 {
 657         return 0;
 658 }
 659
 660 static int skel_pre_reset(struct usb_interface *intf)
 661 {
 662         struct usb_skel *dev = usb_get_intfdata(intf);
 663
 664         mutex_lock(&dev->io_mutex);
 665         skel_draw_down(dev);
 666
 667         return 0;
 668 }
 669
 670 static int skel_post_reset(struct usb_interface *intf)
 671 {
 672         struct usb_skel *dev = usb_get_intfdata(intf);
 673
 674         /* we are sure no URBs are active - no locking needed */
 675         dev->errors = -EPIPE;
 676         mutex_unlock(&dev->io_mutex);
 677
 678         return 0;
 679 }
 680
 681 static struct usb_driver skel_driver = {
 682         .name =         "skeleton",
 683         .probe =        skel_probe,
 684         .disconnect =   skel_disconnect,
 685         .suspend =      skel_suspend,
 686         .resume =       skel_resume,
 687         .pre_reset =    skel_pre_reset,
 688         .post_reset =   skel_post_reset,
 689         .id_table =     skel_table,
 690         .supports_autosuspend = 1,
 691 };
 692
 693 static int __init usb_skel_init(void)
 694 {
 695         int result;
 696
 697         /* register this driver with the USB subsystem */
 698         result = usb_register(&skel_driver);
 699         if (result)
 700                 err("usb_register failed. Error number %d", result);
 701
 702         return result;
 703 }
 704
 705 static void __exit usb_skel_exit(void)
 706 {
 707         /* deregister this driver with the USB subsystem */
 708         usb_deregister(&skel_driver);
 709 }
 710
 711 module_init(usb_skel_init);
 712 module_exit(usb_skel_exit);
 713
 714 MODULE_LICENSE("GPL");