john - 2020-08-12

Hi,
I am using Veracrypt to do some research. Thanks for your work about this amazing project. It really helps a lot for my research work. But I have a technical question about veracrypt.
I plan to create a hidden volume in a USB drive. I detect that during the initialization process, Veracrypt writes some random data to fill the USB drive. My question is, during the initialization process, the USB drive is not mounted (I can not detect any mount point during the initialization process from my Ubuntu), which means the application can not find the USB in OS. So, how does Veracrypt write random data to the USB drive without a mount point?

I also look at the source code but I still can not get the answer. I would appreciate it if you can also tell me the related code part.