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  · DriverStudio          More on WDM Device Interfaces
  · DriverBundle
  · Previews              If you read the previous tip on WDM Device Interfaces, you may have been left
  · Compatibility         wondering how applications actually obtain a path to a device that exports a
 [Downloads]  ·           device interface. This tip shows how to do just that.
 Wizards                  First of all, you must know the class GUID for the device interface that was
  · Utilities             registered by a device that you want to open. For example:
  · NT source
 examples                 static GUID MyDevInterfaceClassGuid =
  · VxD source            { 0x5de30cc0, 0xfef7, 0x11d1, { 0xb3, 0x14, 0x0, 0xc0, 0xd1, 0x57, 0x49, 0x7d } };
 examples
  · WDM source            Next, call SetupDiGetClassDevs, which returns a handle to a device information
 examples                 set. The device information set contains information about all device interfaces
 [Resources]  ·           of the class specified by the GUID. For example:
 Technical papers
  · Useful links          #include
  · Technical tips
 [Support]  ·             HDEVINFO hInfo;
                          DWORD flags = DIGCF_DEVICEINTERFACE | DIGCF_PRESENT;
 Support                  hInfo = SetupDiGetClassDevs(&MyDevInterfaceClassGuid, NULL, NULL, flags);
  · Knowledge base
  · Problem               The next step is to enumerate each of the device interfaces in the device
 submission               information set. The routine that does this is SetupDiEnumDeviceInterfaces. You
  · Product               can call this routine repeatedly, incrementing parameter index each timem, until
 registration             it returns FALSE and GetLastError returns ERROR_NO_MORE_ITEMS.
  · Release notes
 [Shop NuMega]  ·         SP_DEVICE_INTERFACE_DATA DevData;
 Buy it!                  DevData.cbSize = sizeof( SP_DEVICE_INTERFACE_DATA );
  · Price list            DWORD index = 0;
  · How to buy            status = SetupDiEnumDeviceInterfaces(
  · Sales offices                     hInfo,
                                      NULL,
                                      &MyDevInterfaceClassGuid,
 [Y2K Compliance]                     index,
                                      &DevData
                                      );
 [More information]
                          Once you have successfully enumerated a device interface, you can then get
                          detailed information about it. The information is bus or device specific, but
                          always includes at least the pathname for opening the device with CreateFile. To
                          get the detailed information, you call SetupDiGetInterfaceDeviceDetail. You must
                          call this once to get the memory requirement for the buffer, and then a second
                          time to actually get the data. For example:

                          DWORD ReqLen;

                          // first call to get buffer size
                          SetupDiGetInterfaceDeviceDetail (
                              hInfo,
                              &DevData,
                              NULL,
                              0,
                              &ReqLen,
                              NULL
                              );

                          PSP_INTERFACE_DEVICE_DETAIL_DATA DevDetail;
                          DevDetail = PSP_INTERFACE_DEVICE_DETAIL_DATA(new char[ReqLen]);

                          if ( ! DevDetail )
                          {
                                  // error
                          }

                          DevDetail->cbSize = sizeof SP_INTERFACE_DEVICE_DETAIL_DATA;

                          // second call to actually get the data
                          status = SetupDiGetInterfaceDeviceDetail (
                              hInfo,
                              &DevData,
                              DevDetail,
                              ReqLen,
                              &ReqLen,
                              NULL
                              );

                          Finally, you can call CreateFile with the path returned from
                          SetupDiGetInterfaceDeviceDetail:

                          if (status)
                          {
                              HANDLE hDev = CreateFile(
                                  DevDetail->DevicePath,
                                  GENERIC_READ | GENERIC_WRITE,
                                  FILE_SHARE_READ | FILE_SHARE_WRITE,
                                  NULL,
                                  OPEN_EXISTING,
                                  FILE_ATTRIBUTE_NORMAL,
                                  NULL
                                  );
                          }

                          If you are using DriverWorks, there are two new classes in version 2.0,
                          CDeviceInterfaceClass and CDeviceInterface, which simplify these operations for
                          applications.

                          Back to technical tip start page.

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