Error message 'Interface not claimed' from libusb

Question

I'm trying to use libusb, but I am get the following error message:

usbfs: process 24665 (myprogram) did not claim interface 0 before use

I don't really understand why, because as far as I can tell, I'm doing it according to the description found in the library. Here's my code:

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>

#include <libusb.h>

int main(void)
{
    int result;
    struct libusb_device_descriptor desc;
    libusb_device **list;
    libusb_device *my_device = NULL;

    result = libusb_init(NULL);
    libusb_set_debug(NULL, 3);

    ssize_t count = libusb_get_device_list(NULL, &list);
    for (int i = 0; i < count; i++) {
        libusb_device *device = list[i];
        result = libusb_get_device_descriptor(device, &desc);
        if((desc.idVendor == 0x03f0) && (desc.idProduct == 0x241d)) {
            my_device = device;
            break;
         }
    }

    if(my_device != NULL) {
        libusb_device_handle *handle;
        result = libusb_open(my_device, &handle);
        int kernelActive = libusb_kernel_driver_active(handle, 0);
        if(kernelActive == 1) {
            result = libusb_detach_kernel_driver(handle, 0);
        }
        result = libusb_claim_interface (handle, 0);
        result = libusb_control_transfer(handle,0x21,34,0x0003,0,NULL,0,0);
        result = libusb_release_interface (handle, 0);

        if(kernelActive == 1) {
          result = libusb_attach_kernel_driver(handle, 0);
        }
        libusb_close(handle);
    }
    libusb_free_device_list(list, 1);
    libusb_exit(NULL);
    return EXIT_SUCCESS;
}

As you can see, I do claim the interface before the transfer. (I have tried the same code with other USB devices as well, just in case that would have something to do with it.)

I'm using libusb-1.0.9, which is the latest release I could find. I'm running this thing on Ubuntu 12.04_64 (Precise Pangolin).

Answer 1

Just had the same problem with libusb-1.0; I originally had this sequence:

libusb_init
libusb_open_device_with_vid_pid
libusb_reset_device
libusb_get_device
libusb_reset_device
libusb_set_configuration
libusb_claim_interface
libusb_set_interface_alt_setting 
libusb_get_device_descriptor
libusb_get_bus_number 
libusb_get_device_address
libusb_get_string_descriptor_ascii
if(libusb_kernel_driver_active.. ) 
  if(libusb_detach_kernel_driver.. ) 
libusb_bulk_transfer
...

... and for it, the "interface not claimed" was generated when the first libusb_bulk_transfer executed (but not subsequent ones, not shown above), which I confirmed by stepping in gdb. (btw, that error message comes from /linux/drivers/usb/core/devio.c)

This page: USB Hid Issue · Yubico/yubikey-personalization Wiki · GitHub refers to a fix for libusb-0.1 which called the corresponding "detach_driver" function; so I started moving the "detach_driver" part around in my code too - and finally this sequence seems to get rid of the "interface not claimed" message:

libusb_init
libusb_open_device_with_vid_pid
if(libusb_kernel_driver_active.. ) 
  if(libusb_detach_kernel_driver.. ) 
libusb_reset_device
libusb_get_device
libusb_set_configuration
libusb_claim_interface
libusb_set_interface_alt_setting 
libusb_get_device_descriptor
libusb_get_bus_number
libusb_get_device_address
libusb_get_string_descriptor_ascii
libusb_bulk_transfer
...

Apparently, if the driver is first detached, and then interface is claimed - then no errors are generated. But that is also what you have in OP there - so I think, the trick for OP would be to have detach, then set configuration, and after that claim interface...

Hope this helps,
Cheers!