How to get the serial number of non-MFi USB?

I am developing an iOS program which is using UIDocumentPickerViewController to get the content of USB. It's OK. But I also need to get the serial number of USB. For MFi USB, I can use EAAccessoryManager to get the serial number, but it cannot apply to non-MFi USB. Is there any method to get the serial number of non-MFi USB?

Jacks Hung