A File Manager extension sends an FM_GETDRIVEINFO message to retrieve drive information from the active File Manager window.
FM_GETDRIVEINFO wParam = 0; // not used, must be zero lParam = (LPARAM) (LPFMS_GETDRIVEINFO) lpfmsgdi; // drive data
The return value is always nonzero.
If 0xFFFFFFFF is returned in the dwTotalSpace or dwFreeSpace member of the FMS_GETDRIVEINFO structure, the extension library must compute the value or values.