IOCTL_STORAGE_GET_DEVICE_NUMBER control code
Returns a STORAGE_DEVICE_NUMBER structure that contains the FILE_DEVICE_XXX type, device number, and, for a partitionable device, the partition number assigned to a device by the driver when the device is started. This request is usually issued by a fault-tolerant disk driver.
Parameters.DeviceIoControl.OutputBufferLength in the I/O stack location indicates the size, in bytes, of the parameter buffer, which must be >= sizeof(STORAGE_DEVICE_NUMBER).
The driver returns the STORAGE_DEVICE_NUMBER data in the buffer at Irp->AssociatedIrp.SystemBuffer.
The Information field is set to the number of bytes returned. The Status field is set to STATUS_SUCCESS, or possibly to STATUS_INSUFFICIENT_RESOURCES.