So I am working on a project that's related to the Kernel code(specifically related to the TCP/IP stack of the kernel).

I need to build some models to describe the functionality and components of my system. Initially I thought about Class Diagram, it can describe the general architecture of my system but it doesn't make sense since my code is VERY structured(written in standard C).

I also thought about DFDs, they'd describe the processes of my system, and how the data is flowing. But they contain something which doesn't really fit in; data-storages. I have no databases here(at all).

For the functionality, other team members suggested using Activity and Sequence diagrams, which is kinda okay with me, but what about the system components?

So basically my question is; I want to describe the components of my system; what do you suggest as a meaningful diagram to follow? (Again, the project is a research low-level systems-oriented project with almost no user-interface at all)