src/chrome/browser/usb/usb_device_handle.cc

   1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "chrome/browser/usb/usb_device_handle.h"
   6
   7 #include <algorithm>
   8 #include <vector>
   9
  10 #include "base/message_loop/message_loop.h"
  11 #include "base/stl_util.h"
  12 #include "base/strings/string16.h"
  13 #include "base/synchronization/lock.h"
  14 #include "chrome/browser/usb/usb_context.h"
  15 #include "chrome/browser/usb/usb_device.h"
  16 #include "chrome/browser/usb/usb_interface.h"
  17 #include "chrome/browser/usb/usb_service.h"
  18 #include "content/public/browser/browser_thread.h"
  19 #include "third_party/libusb/src/libusb/libusb.h"
  20
  21 using content::BrowserThread;
  22 void HandleTransferCompletion(PlatformUsbTransferHandle transfer);
  23
  24 namespace {
  25
  26 static uint8 ConvertTransferDirection(
  27     const UsbEndpointDirection direction) {
  28   switch (direction) {
  29     case USB_DIRECTION_INBOUND:
  30       return LIBUSB_ENDPOINT_IN;
  31     case USB_DIRECTION_OUTBOUND:
  32       return LIBUSB_ENDPOINT_OUT;
  33     default:
  34       NOTREACHED();
  35       return LIBUSB_ENDPOINT_IN;
  36   }
  37 }
  38
  39 static uint8 CreateRequestType(const UsbEndpointDirection direction,
  40     const UsbDeviceHandle::TransferRequestType request_type,
  41     const UsbDeviceHandle::TransferRecipient recipient) {
  42   uint8 result = ConvertTransferDirection(direction);
  43
  44   switch (request_type) {
  45     case UsbDeviceHandle::STANDARD:
  46       result |= LIBUSB_REQUEST_TYPE_STANDARD;
  47       break;
  48     case UsbDeviceHandle::CLASS:
  49       result |= LIBUSB_REQUEST_TYPE_CLASS;
  50       break;
  51     case UsbDeviceHandle::VENDOR:
  52       result |= LIBUSB_REQUEST_TYPE_VENDOR;
  53       break;
  54     case UsbDeviceHandle::RESERVED:
  55       result |= LIBUSB_REQUEST_TYPE_RESERVED;
  56       break;
  57   }
  58
  59   switch (recipient) {
  60     case UsbDeviceHandle::DEVICE:
  61       result |= LIBUSB_RECIPIENT_DEVICE;
  62       break;
  63     case UsbDeviceHandle::INTERFACE:
  64       result |= LIBUSB_RECIPIENT_INTERFACE;
  65       break;
  66     case UsbDeviceHandle::ENDPOINT:
  67       result |= LIBUSB_RECIPIENT_ENDPOINT;
  68       break;
  69     case UsbDeviceHandle::OTHER:
  70       result |= LIBUSB_RECIPIENT_OTHER;
  71       break;
  72   }
  73
  74   return result;
  75 }
  76
  77 static UsbTransferStatus ConvertTransferStatus(
  78     const libusb_transfer_status status) {
  79   switch (status) {
  80     case LIBUSB_TRANSFER_COMPLETED:
  81       return USB_TRANSFER_COMPLETED;
  82     case LIBUSB_TRANSFER_ERROR:
  83       return USB_TRANSFER_ERROR;
  84     case LIBUSB_TRANSFER_TIMED_OUT:
  85       return USB_TRANSFER_TIMEOUT;
  86     case LIBUSB_TRANSFER_STALL:
  87       return USB_TRANSFER_STALLED;
  88     case LIBUSB_TRANSFER_NO_DEVICE:
  89       return USB_TRANSFER_DISCONNECT;
  90     case LIBUSB_TRANSFER_OVERFLOW:
  91       return USB_TRANSFER_OVERFLOW;
  92     case LIBUSB_TRANSFER_CANCELLED:
  93       return USB_TRANSFER_CANCELLED;
  94     default:
  95       NOTREACHED();
  96       return USB_TRANSFER_ERROR;
  97   }
  98 }
  99
 100 static void LIBUSB_CALL PlatformTransferCompletionCallback(
 101     PlatformUsbTransferHandle transfer) {
 102   BrowserThread::PostTask(BrowserThread::FILE,
 103                           FROM_HERE,
 104                           base::Bind(HandleTransferCompletion, transfer));
 105 }
 106
 107 }  // namespace
 108
 109 void HandleTransferCompletion(PlatformUsbTransferHandle transfer) {
 110   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
 111   UsbDeviceHandle* const device_handle =
 112       reinterpret_cast<UsbDeviceHandle*>(transfer->user_data);
 113   CHECK(device_handle) << "Device handle is closed before transfer finishes.";
 114   device_handle->TransferComplete(transfer);
 115   libusb_free_transfer(transfer);
 116 }
 117
 118
 119 class UsbDeviceHandle::InterfaceClaimer
 120     : public base::RefCountedThreadSafe<UsbDeviceHandle::InterfaceClaimer> {
 121  public:
 122   InterfaceClaimer(const scoped_refptr<UsbDeviceHandle> handle,
 123                    const int interface_number);
 124
 125   bool Claim() const;
 126
 127   int alternate_setting() const { return alternate_setting_; }
 128   void set_alternate_setting(const int alternate_setting) {
 129     alternate_setting_ = alternate_setting;
 130   }
 131
 132  private:
 133   friend class UsbDevice;
 134   friend class base::RefCountedThreadSafe<InterfaceClaimer>;
 135   ~InterfaceClaimer();
 136
 137   const scoped_refptr<UsbDeviceHandle> handle_;
 138   const int interface_number_;
 139   int alternate_setting_;
 140
 141   DISALLOW_COPY_AND_ASSIGN(InterfaceClaimer);
 142 };
 143
 144 UsbDeviceHandle::InterfaceClaimer::InterfaceClaimer(
 145     const scoped_refptr<UsbDeviceHandle> handle, const int interface_number)
 146     : handle_(handle),
 147       interface_number_(interface_number),
 148       alternate_setting_(0) {
 149 }
 150
 151 UsbDeviceHandle::InterfaceClaimer::~InterfaceClaimer() {
 152   libusb_release_interface(handle_->handle(), interface_number_);
 153 }
 154
 155 bool UsbDeviceHandle::InterfaceClaimer::Claim() const {
 156   return libusb_claim_interface(handle_->handle(), interface_number_) == 0;
 157 }
 158
 159 struct UsbDeviceHandle::Transfer {
 160   Transfer();
 161   ~Transfer();
 162
 163   UsbTransferType transfer_type;
 164   scoped_refptr<net::IOBuffer> buffer;
 165   scoped_refptr<UsbDeviceHandle::InterfaceClaimer> claimed_interface;
 166   scoped_refptr<base::MessageLoopProxy> message_loop_proxy;
 167   size_t length;
 168   UsbTransferCallback callback;
 169 };
 170
 171 UsbDeviceHandle::Transfer::Transfer()
 172     : transfer_type(USB_TRANSFER_CONTROL),
 173       length(0) {
 174 }
 175
 176 UsbDeviceHandle::Transfer::~Transfer() {}
 177
 178 UsbDeviceHandle::UsbDeviceHandle(
 179     scoped_refptr<UsbContext> context,
 180     UsbDevice* device,
 181     PlatformUsbDeviceHandle handle,
 182     scoped_refptr<UsbConfigDescriptor> interfaces)
 183     : device_(device),
 184       handle_(handle),
 185       interfaces_(interfaces),
 186       context_(context) {
 187   DCHECK(thread_checker_.CalledOnValidThread());
 188   DCHECK(handle) << "Cannot create device with NULL handle.";
 189   DCHECK(interfaces_) << "Unabled to list interfaces";
 190 }
 191
 192 UsbDeviceHandle::UsbDeviceHandle() : device_(NULL), handle_(NULL) {
 193 }
 194
 195 UsbDeviceHandle::~UsbDeviceHandle() {
 196   DCHECK(thread_checker_.CalledOnValidThread());
 197
 198   libusb_close(handle_);
 199   handle_ = NULL;
 200 }
 201
 202 scoped_refptr<UsbDevice> UsbDeviceHandle::device() const {
 203   return device_;
 204 }
 205
 206 void UsbDeviceHandle::Close() {
 207   DCHECK(thread_checker_.CalledOnValidThread());
 208   if (device_)
 209     device_->Close(this);
 210 }
 211
 212 void UsbDeviceHandle::TransferComplete(PlatformUsbTransferHandle handle) {
 213   DCHECK(ContainsKey(transfers_, handle)) << "Missing transfer completed";
 214
 215   Transfer transfer = transfers_[handle];
 216   transfers_.erase(handle);
 217
 218   DCHECK_GE(handle->actual_length, 0) << "Negative actual length received";
 219   size_t actual_length =
 220       static_cast<size_t>(std::max(handle->actual_length, 0));
 221
 222   DCHECK(transfer.length >= actual_length) <<
 223       "data too big for our buffer (libusb failure?)";
 224
 225   scoped_refptr<net::IOBuffer> buffer = transfer.buffer;
 226   switch (transfer.transfer_type) {
 227     case USB_TRANSFER_CONTROL:
 228       // If the transfer is a control transfer we do not expose the control
 229       // setup header to the caller. This logic strips off the header if
 230       // present before invoking the callback provided with the transfer.
 231       if (actual_length > 0) {
 232         CHECK(transfer.length >= LIBUSB_CONTROL_SETUP_SIZE) <<
 233             "buffer was not correctly set: too small for the control header";
 234
 235         if (transfer.length >= actual_length &&
 236             actual_length >= LIBUSB_CONTROL_SETUP_SIZE) {
 237           // If the payload is zero bytes long, pad out the allocated buffer
 238           // size to one byte so that an IOBuffer of that size can be allocated.
 239           scoped_refptr<net::IOBuffer> resized_buffer = new net::IOBuffer(
 240               std::max(actual_length, static_cast<size_t>(1)));
 241           memcpy(resized_buffer->data(),
 242                  buffer->data() + LIBUSB_CONTROL_SETUP_SIZE,
 243                  actual_length);
 244           buffer = resized_buffer;
 245         }
 246       }
 247       break;
 248
 249     case USB_TRANSFER_ISOCHRONOUS:
 250       // Isochronous replies might carry data in the different isoc packets even
 251       // if the transfer actual_data value is zero. Furthermore, not all of the
 252       // received packets might contain data, so we need to calculate how many
 253       // data bytes we are effectively providing and pack the results.
 254       if (actual_length == 0) {
 255         size_t packet_buffer_start = 0;
 256         for (int i = 0; i < handle->num_iso_packets; ++i) {
 257           PlatformUsbIsoPacketDescriptor packet = &handle->iso_packet_desc[i];
 258           if (packet->actual_length > 0) {
 259             // We don't need to copy as long as all packets until now provide
 260             // all the data the packet can hold.
 261             if (actual_length < packet_buffer_start) {
 262               CHECK(packet_buffer_start + packet->actual_length <=
 263                     transfer.length);
 264               memmove(buffer->data() + actual_length,
 265                       buffer->data() + packet_buffer_start,
 266                       packet->actual_length);
 267             }
 268             actual_length += packet->actual_length;
 269           }
 270
 271           packet_buffer_start += packet->length;
 272         }
 273       }
 274       break;
 275
 276     case USB_TRANSFER_BULK:
 277     case USB_TRANSFER_INTERRUPT:
 278       break;
 279
 280     default:
 281       NOTREACHED() << "Invalid usb transfer type";
 282       break;
 283   }
 284
 285   transfer.message_loop_proxy->PostTask(
 286       FROM_HERE,
 287       base::Bind(transfer.callback,
 288                  ConvertTransferStatus(handle->status),
 289                  buffer,
 290                  actual_length));
 291
 292   // Must release interface first before actually delete this.
 293   transfer.claimed_interface = NULL;
 294 }
 295
 296 bool UsbDeviceHandle::ClaimInterface(const int interface_number) {
 297   DCHECK(thread_checker_.CalledOnValidThread());
 298   if (!device_) return false;
 299   if (ContainsKey(claimed_interfaces_, interface_number)) return true;
 300
 301   scoped_refptr<InterfaceClaimer> claimer =
 302       new InterfaceClaimer(this, interface_number);
 303
 304   if (claimer->Claim()) {
 305     claimed_interfaces_[interface_number]= claimer;
 306     RefreshEndpointMap();
 307     return true;
 308   }
 309   return false;
 310 }
 311
 312 bool UsbDeviceHandle::ReleaseInterface(const int interface_number) {
 313   DCHECK(thread_checker_.CalledOnValidThread());
 314   if (!device_) return false;
 315   if (!ContainsKey(claimed_interfaces_, interface_number)) return false;
 316
 317   // Cancel all the transfers on that interface.
 318   InterfaceClaimer* interface_claimer =
 319       claimed_interfaces_[interface_number].get();
 320   for (TransferMap::iterator it = transfers_.begin();
 321       it != transfers_.end(); ++it) {
 322     if (it->second.claimed_interface.get() == interface_claimer)
 323       libusb_cancel_transfer(it->first);
 324   }
 325   claimed_interfaces_.erase(interface_number);
 326
 327   RefreshEndpointMap();
 328   return true;
 329 }
 330
 331 bool UsbDeviceHandle::SetInterfaceAlternateSetting(
 332     const int interface_number,
 333     const int alternate_setting) {
 334   DCHECK(thread_checker_.CalledOnValidThread());
 335   if (!device_) return false;
 336   if (!ContainsKey(claimed_interfaces_, interface_number)) return false;
 337   const int rv = libusb_set_interface_alt_setting(handle_,
 338       interface_number, alternate_setting);
 339   if (rv == 0) {
 340     claimed_interfaces_[interface_number]->
 341       set_alternate_setting(alternate_setting);
 342     RefreshEndpointMap();
 343     return true;
 344   }
 345   return false;
 346 }
 347
 348 bool UsbDeviceHandle::ResetDevice() {
 349   DCHECK(thread_checker_.CalledOnValidThread());
 350   if (!device_) return false;
 351
 352   return libusb_reset_device(handle_) == 0;
 353 }
 354
 355 bool UsbDeviceHandle::GetSerial(base::string16* serial) {
 356   DCHECK(thread_checker_.CalledOnValidThread());
 357   PlatformUsbDevice device = libusb_get_device(handle_);
 358   libusb_device_descriptor desc;
 359
 360   if (libusb_get_device_descriptor(device, &desc) != LIBUSB_SUCCESS)
 361     return false;
 362
 363   if (desc.iSerialNumber == 0)
 364     return false;
 365
 366   // Getting supported language ID.
 367   uint16 langid[128] = { 0 };
 368
 369   int size = libusb_get_string_descriptor(
 370       handle_, 0, 0,
 371       reinterpret_cast<unsigned char*>(&langid[0]), sizeof(langid));
 372   if (size < 0)
 373     return false;
 374
 375   int language_count = (size - 2) / 2;
 376
 377   for (int i = 1; i <= language_count; ++i) {
 378     // Get the string using language ID.
 379     base::char16 text[256] = { 0 };
 380     size = libusb_get_string_descriptor(
 381         handle_, desc.iSerialNumber, langid[i],
 382         reinterpret_cast<unsigned char*>(&text[0]), sizeof(text));
 383     if (size <= 2)
 384       continue;
 385     if ((text[0] >> 8) != LIBUSB_DT_STRING)
 386       continue;
 387     if ((text[0] & 255) > size)
 388       continue;
 389
 390     size = size / 2 - 1;
 391     *serial = base::string16(text + 1, size);
 392     return true;
 393   }
 394   return false;
 395 }
 396
 397 void UsbDeviceHandle::ControlTransfer(const UsbEndpointDirection direction,
 398     const TransferRequestType request_type, const TransferRecipient recipient,
 399     const uint8 request, const uint16 value, const uint16 index,
 400     net::IOBuffer* buffer, const size_t length, const unsigned int timeout,
 401     const UsbTransferCallback& callback) {
 402   if (!device_) {
 403     callback.Run(USB_TRANSFER_DISCONNECT, buffer, 0);
 404     return;
 405   }
 406
 407   const size_t resized_length = LIBUSB_CONTROL_SETUP_SIZE + length;
 408   scoped_refptr<net::IOBuffer> resized_buffer(new net::IOBufferWithSize(
 409       resized_length));
 410   memcpy(resized_buffer->data() + LIBUSB_CONTROL_SETUP_SIZE, buffer->data(),
 411          length);
 412
 413   PlatformUsbTransferHandle const transfer = libusb_alloc_transfer(0);
 414   const uint8 converted_type = CreateRequestType(direction, request_type,
 415                                                  recipient);
 416   libusb_fill_control_setup(reinterpret_cast<uint8*>(resized_buffer->data()),
 417                             converted_type, request, value, index, length);
 418   libusb_fill_control_transfer(
 419       transfer,
 420       handle_,
 421       reinterpret_cast<uint8*>(resized_buffer->data()),
 422       PlatformTransferCompletionCallback,
 423       this,
 424       timeout);
 425
 426   BrowserThread::PostTask(
 427       BrowserThread::FILE,
 428       FROM_HERE,
 429       base::Bind(&UsbDeviceHandle::SubmitTransfer,
 430                  this,
 431                  transfer,
 432                  USB_TRANSFER_CONTROL,
 433                  resized_buffer,
 434                  resized_length,
 435                  base::MessageLoopProxy::current(),
 436                  callback));
 437 }
 438
 439 void UsbDeviceHandle::BulkTransfer(const UsbEndpointDirection direction,
 440     const uint8 endpoint, net::IOBuffer* buffer, const size_t length,
 441     const unsigned int timeout, const UsbTransferCallback& callback) {
 442   if (!device_) {
 443     callback.Run(USB_TRANSFER_DISCONNECT, buffer, 0);
 444     return;
 445   }
 446
 447   PlatformUsbTransferHandle const transfer = libusb_alloc_transfer(0);
 448   const uint8 new_endpoint = ConvertTransferDirection(direction) | endpoint;
 449   libusb_fill_bulk_transfer(transfer, handle_, new_endpoint,
 450       reinterpret_cast<uint8*>(buffer->data()), length,
 451       PlatformTransferCompletionCallback, this, timeout);
 452
 453   BrowserThread::PostTask(
 454       BrowserThread::FILE,
 455       FROM_HERE,
 456       base::Bind(&UsbDeviceHandle::SubmitTransfer,
 457                  this,
 458                  transfer,
 459                  USB_TRANSFER_BULK,
 460                  make_scoped_refptr(buffer),
 461                  length,
 462                  base::MessageLoopProxy::current(),
 463                  callback));
 464 }
 465
 466 void UsbDeviceHandle::InterruptTransfer(const UsbEndpointDirection direction,
 467     const uint8 endpoint, net::IOBuffer* buffer, const size_t length,
 468     const unsigned int timeout, const UsbTransferCallback& callback) {
 469   if (!device_) {
 470     callback.Run(USB_TRANSFER_DISCONNECT, buffer, 0);
 471     return;
 472   }
 473
 474   PlatformUsbTransferHandle const transfer = libusb_alloc_transfer(0);
 475   const uint8 new_endpoint = ConvertTransferDirection(direction) | endpoint;
 476   libusb_fill_interrupt_transfer(transfer, handle_, new_endpoint,
 477       reinterpret_cast<uint8*>(buffer->data()), length,
 478       PlatformTransferCompletionCallback, this, timeout);
 479   BrowserThread::PostTask(
 480       BrowserThread::FILE,
 481       FROM_HERE,
 482       base::Bind(&UsbDeviceHandle::SubmitTransfer,
 483                  this,
 484                  transfer,
 485                  USB_TRANSFER_INTERRUPT,
 486                  make_scoped_refptr(buffer),
 487                  length,
 488                  base::MessageLoopProxy::current(),
 489                  callback));
 490 }
 491
 492 void UsbDeviceHandle::IsochronousTransfer(const UsbEndpointDirection direction,
 493     const uint8 endpoint, net::IOBuffer* buffer, const size_t length,
 494     const unsigned int packets, const unsigned int packet_length,
 495     const unsigned int timeout, const UsbTransferCallback& callback) {
 496   if (!device_) {
 497     callback.Run(USB_TRANSFER_DISCONNECT, buffer, 0);
 498     return;
 499   }
 500
 501   const uint64 total_length = packets * packet_length;
 502   CHECK(packets <= length && total_length <= length) <<
 503       "transfer length is too small";
 504
 505   PlatformUsbTransferHandle const transfer = libusb_alloc_transfer(packets);
 506   const uint8 new_endpoint = ConvertTransferDirection(direction) | endpoint;
 507   libusb_fill_iso_transfer(transfer, handle_, new_endpoint,
 508       reinterpret_cast<uint8*>(buffer->data()), length, packets,
 509       PlatformTransferCompletionCallback, this, timeout);
 510   libusb_set_iso_packet_lengths(transfer, packet_length);
 511
 512   BrowserThread::PostTask(
 513       BrowserThread::FILE,
 514       FROM_HERE,
 515       base::Bind(&UsbDeviceHandle::SubmitTransfer,
 516                  this,
 517                  transfer,
 518                  USB_TRANSFER_ISOCHRONOUS,
 519                  make_scoped_refptr(buffer),
 520                  length,
 521                  base::MessageLoopProxy::current(),
 522                  callback));
 523 }
 524
 525 void UsbDeviceHandle::RefreshEndpointMap() {
 526   DCHECK(thread_checker_.CalledOnValidThread());
 527   endpoint_map_.clear();
 528   for (ClaimedInterfaceMap::iterator it = claimed_interfaces_.begin();
 529       it != claimed_interfaces_.end(); ++it) {
 530     scoped_refptr<const UsbInterfaceAltSettingDescriptor> interface_desc =
 531         interfaces_->GetInterface(it->first)->GetAltSetting(
 532             it->second->alternate_setting());
 533     for (size_t i = 0; i < interface_desc->GetNumEndpoints(); i++) {
 534       scoped_refptr<const UsbEndpointDescriptor> endpoint =
 535           interface_desc->GetEndpoint(i);
 536       endpoint_map_[endpoint->GetAddress()] = it->first;
 537     }
 538   }
 539 }
 540
 541 scoped_refptr<UsbDeviceHandle::InterfaceClaimer>
 542     UsbDeviceHandle::GetClaimedInterfaceForEndpoint(unsigned char endpoint) {
 543   unsigned char address = endpoint & LIBUSB_ENDPOINT_ADDRESS_MASK;
 544   if (ContainsKey(endpoint_map_, address))
 545     return claimed_interfaces_[endpoint_map_[address]];
 546   return NULL;
 547 }
 548
 549 void UsbDeviceHandle::SubmitTransfer(
 550     PlatformUsbTransferHandle handle,
 551     UsbTransferType transfer_type,
 552     net::IOBuffer* buffer,
 553     const size_t length,
 554     scoped_refptr<base::MessageLoopProxy> message_loop_proxy,
 555     const UsbTransferCallback& callback) {
 556   DCHECK(thread_checker_.CalledOnValidThread());
 557   if (!device_) {
 558     message_loop_proxy->PostTask(
 559         FROM_HERE,
 560         base::Bind(callback, USB_TRANSFER_DISCONNECT,
 561                    make_scoped_refptr(buffer), 0));
 562   }
 563
 564   Transfer transfer;
 565   transfer.transfer_type = transfer_type;
 566   transfer.buffer = buffer;
 567   transfer.length = length;
 568   transfer.callback = callback;
 569   transfer.message_loop_proxy = message_loop_proxy;
 570
 571   // It's OK for this method to return NULL. libusb_submit_transfer will fail if
 572   // it requires an interface we didn't claim.
 573   transfer.claimed_interface = GetClaimedInterfaceForEndpoint(handle->endpoint);
 574
 575   if (libusb_submit_transfer(handle) == LIBUSB_SUCCESS) {
 576     transfers_[handle] = transfer;
 577   } else {
 578     message_loop_proxy->PostTask(
 579         FROM_HERE,
 580         base::Bind(callback, USB_TRANSFER_ERROR,
 581                    make_scoped_refptr(buffer), 0));
 582   }
 583 }
 584
 585 void UsbDeviceHandle::InternalClose() {
 586   DCHECK(thread_checker_.CalledOnValidThread());
 587   if (!device_) return;
 588
 589   // Cancel all the transfers.
 590   for (TransferMap::iterator it = transfers_.begin();
 591       it != transfers_.end(); ++it) {
 592     // The callback will be called some time later.
 593     libusb_cancel_transfer(it->first);
 594   }
 595
 596   // Attempt-release all the interfaces.
 597   // It will be retained until the transfer cancellation is finished.
 598   claimed_interfaces_.clear();
 599
 600   // Cannot close device handle here. Need to wait for libusb_cancel_transfer to
 601   // finish.
 602   device_ = NULL;
 603 }