about \'FT_BALANCE_READ_MODE\' IoControlCode ?

Hello,

Working on a usb card reader project (usb mass storage device),

I think this IoControlCode is sent from partition manager driver (partmgr.sys) to disk class driver , but it does not appear when I install my driver . all of the privie io action seem are correct ,and the return data are same with microsoft leagcy driver(usbstor.sys). I need to know what this IoControlCode is more complete in order to easier find out the problem. it is not explaned in DDK document.

Thanks.