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>>>> + >>>> + return 0; >>>> +} >>>> +late_initcall(bpf_emit_btf_type); >>> >>> I think if we burn a dummy function on this it would be a wrong >>> pattern to follow. >> >> Maybe we can pick another initcall to piggyback? >> >>> This is just a nop C statement. >>> Typically we add BUILD_BUG_ON near the places that rely on that constraint. >>> There is such a function already. It's tcp_set_state() as you pointed out. >>> It's not using BTF of course, but I would move above BTF_TYPE_EMIT_ENUM there. >>> I'm not sure why you're calling it "pollute net/ipv4/tcp.c". >> >> This is the minor reason. I first coded in that place and feel awkward >> where we have macro referenced above and we still emit a BTF_TYPE_EMIT >> below although with some comments. >> >> The major reason is I think we may have some uapi type/enum's (e.g., in >> uapi/linux/bpf.h) which will be used in bpf program but not in kernel >> itself. So we cannot generate types in vmlinux btf because of this. So I >> used this case to find a place to generate these btf types. >> BPF_TCP_CLOSE is actually such an example, it happens we have a >> BUILD_BUG_ON in kernel to access it. >> Maybe I am too forward looking? > > It's great to be forward looking :) > I'm just having a hard time justifying an empty function with single 'ret' insn > that actually will be called at init time and it will stay empty like this for > foreseeable future. Static analysis tools and whatnot will start sending > patches to remove that empty function. Okay, will go back to net/ipv4/tcp.c approach. We can address missing uapi type issue later if it ever comes up. Thanks!