I am converting code from C to rust.
There is too much code so the transition must be done in steps.
Some struct variables have the volatile modifier, so I have to find a way to generate struct variables with volatile to ensure the C code behaves the same during the transition and everything can be tested.

On the rust side volatile behavior is achieved by using read_volatile/write_volatile manually or with a wrapper.
On the C side the variables must have the volatile modifier or I must cast every singe use of the variable to a volatile type (untested).

I am looking for a solution that avoids having to modify the original C code.
The ideal solution would be cbindgen generating the volatile modifier in specific struct variables, which allows me to change the structure at a later stage while ensuring the remaining C code behaves the same.

So, how do I mark a struct variable volatile?