btf/cmd/genbtftypes: (#1218) a generator that generates btf_types.go

[OmarTariq612]

This is guaranteed to match the kernel struct defenitions.

I've tried to generate those structs in the sys package (sys/types.go) but there are private methods so I've tried to write those method manually after generating the types but there were other dependencies (constants like btfMagic, types like FwdKind).

Related to #1218

[ti-mo]

@OmarTariq612 What's the benefit of having these be auto-generated? This adds 10x the amount of code to maintain to generate a handful of structs with a few fields, and these rarely change. I think @lmb's comment in the issue was just about moving the struct definitions into sys, not auto-generating them. Not all code in sys is autogenerated.

[lmb]

Hi @OmarTariq612, thanks for your PR :) Contrary to what Timo says, I did mean to auto generate the types. I think he has a point that having a separate binary to do the generation is not necessary.

The code to generate the types can just live in gentypes, and the generated types can be move to and exported from internal/sys instead of btf. The btf types can just go into sys/types.go as well. Is that something you're up for?

[OmarTariq612]

I closed the PR by mistake, I'm still working on this.

[OmarTariq612]

@ti-mo the migration is not easy, generating those types in internal/sys forces us to implement the methods there and those methods depend on (ex: btf.FwdKind, internal.DiscardZeroes, ...), trying to use those from internal/sys introduces a cycle, do you have a suggestion ?