If you want to pass through a smart card reader, you need to specify the reader with the --device= tag. The method used depends on how the reader is recognized. The first is /dev/ttyUSBX. To find the correct device, connect the reader and run dmesg | tail on the host. In the output you will find /dev/ttyUSBX, where X is the number of the device. If this is the first reader you connect to your host, it will be /dev/ttyUSB0. If you add one more it will be /dev/ttyUSB1.
If there are no /dev/ttyUSBX device in dmesg | tail, you have to use the USB bus path. It will look similar to the below.
/dev/bus/usb/001/001
The important parts are the two numbers in the end. The first one is the Bus number, the second is the Device number. To find the Bus and Device number you have to run lsusb on the host, then find your USB device in the list and note the Bus and Device numbers.
Here is an example of how to find the Bus and Device. The output of the lsusb command is below.
Bus 002 Device 005: ID 076b:6622 OmniKey AG CardMan 6121
The first number, the Bus, is 002. The second number, the Device, is 005. This will look like below in the --device= tag.
--device=/dev/bus/usb/002/005
If you have multiple smart card readers, you add one --device= tag for each reader.