How to get opened/used files of a running process

I try to figure out a way to get the used files of a process to show which files are currently opened / used by this process.

I have found Listing Used Files.

Is 开发者_JAVA百科there a link to get this in C#?

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The NtQuerySystemInformation function seems like a logical starting point, but you'd have to access it via P/Invoke.

From my googling it seems like many people have thought of this approach in the past, but it has never been documented (at least not on PInvoke.net).