Collect an information about suspended USB devices via IOUSBDeviceInterface245

Question

I'm trying to get some information (such a product name) via IOUSBDeviceInterface245 (from IOKit on Mac OS X):
Code #1

io_iterator_t iterator;
io_object_t   usb_device  
SInt32 score = 0;
kern_return_t kr = IOServiceGetMatchingServices(kIOMasterPortDefault,     
                                           IOServiceNameMatching("AppleUSBOHCI"),    
                                           &iterator);   
IOCFPlugInInterface     **plugin_interface = NULL; 
IOUSBDeviceInterface245 **usb_interface    = NULL;
// ...
// enumerate devices (usb_device = IOIteratorNext(iterator))
// ...
IOReturn return_code = IOCreatePlugInInterfaceForService(usb_device,  
                                                  kIOUSBDeviceUserClientTypeID, 
                                                  kIOCFPlugInInterfaceID,  
                                                  &plugin_interface,
                                                  &score);
HRESULT h_result = (*pluginInterface)->QueryInterface(pluginInterface,
                                  CFUUIDGetUUIDBytes(kIOUSBDeviceInterfaceID245), 
                                  (LPVOID)&usb_interface);
IODestroyPlugInInterface(pluginInterface);

UInt8 product_string_index;
return_code = (*usb_interface)->USBGetProductStringIndex(usb_interface,  
                                                         &product_string_index);
// Next, getting a product string by string's index. To do so, we need to send  
// IOUSBDevRequest (with type "kUSBRqGetDescriptor") to the current USB-device.
// Code bellow - is a pseudocode:
char *product_name = malloc(128);
get_string_by_index(usb_interface, product_string_index, product_string, 128);

This code is working well for all working-now devices, but it doesn't working for suspended ("sleeping")
devices (product_name is just a blank string).

But, if I using this code:
Code #2

 CFMutableDictionaryRef child_properties = CFDictionaryCreateMutable(NULL, 0,  
                                                                NULL,NULL);
 kern_return_t kr;
 io_service_t io_service;
 // iterator = iterator for "AppleUSBOHCI" or "AppleUSBEHCI" services
 while((io_service = IOIteratorNext(iterator))) {      
    io_iterator_t   children_iterator;
    kernel_return = IORegistryEntryGetChildIterator(io_service, kIOServicePlane,  
                                                   &children_iterator);
    io_registry_entry_t child;
    while((child = IOIteratorNext(children_iterator))) {
      // Create a CFDictionary with usb-device's properties
      IORegistryEntryCreateCFProperties(child, &child_properties,  
                                        kCFAllocatorDefault, 
                                        kNilOptions);
      NSLog(@"%@",[(NSDictionary*)child_properties valueForKey:@"USB Product Name"]);
    }
  }

that's working for all devices at all (I don't know why).

I tried to wakeup a suspended devices by this code (using with the code #1):

(*usb_interface)->USBDeviceSuspend(usb_interface, false);

but it's changed nothing.

One thing that I noticed - the code #1 is fully working for all properties of sleeping devices, except string values (which getting by string's index).

UPDATE:
So, my question is how can I unsuspend a device for using with the first code block?
Thank you.

Answer 1

You can't read the string from a suspended device (as in code #1) as it is read directly from the device (which can't respond, as it is suspended). To read these directly, you will need to unsuspend the device first (which may be a bad idea if it was suspended by a driver, also, remember to check for success)

If you want to read the standard strings, use the second code block (which reads the properties, which were already fetched from the device)