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