I am developing a smartcard UMDF windows driver. I would like to achieve following behaviour:
When listing all connected readers by using API call SCardListReaders I want to retrieve the correct friendly names for each attached reader. So for example if I have two readers of same brand I want this to be returned by the driver:
SmartcardBrand USBReader 0
SmartcardBrand USBReader 1
I know that the friendly name is composed of the attributes SCARD_ATTR_VENDOR_NAME, SCARD_ATTR_VENDOR_IFD_TYPE and SCARD_ATTR_DEVICE_UNIT the driver returns.
My question is, in my driver, how can I distinguish between SmartcardBrand USBReader 0 and SmartcardBrand USBReader 1?
What shall I return to the OS when SCARD_ATTR_DEVICE_UNIT is requested. I cannot use and increment a global static variable in my driver because every time a new reader gets connected a new UMDF host process is launched (I can see it in the task manager) resulting in a separate new memory area.
What is the proper way of counting device instances in a UMDF driver?
I solved the problem by using memory-mapped files. Basically each UMDF process of my driver creates a memory-mapped file with name of the reader's friendly name. When an other process tries to create a file with the same name it indicates that a driver is already running.
However, there is inconsistency when I connect a reader which uses my driver and afterwards connect a reader which uses Windows native driver. The Windows driver will not see my memory-mapped file I created and apply index 0 for its device.
I found out that, when the Windows driver is loaded it queries SCARD_ATTR_VENDOR_IFD_TYPE, SCARD_ATTR_VENDOR_IFD_TYPE and SCARD_ATTR_DEVICE_UNIT from my driver (and from all other drivers currently loaded). I guess this way the Windows driver can know which device units are taken and apply a free one to its reader.
