netdev - Re: [PATCH bpf-next 0/4] libbpf: add raw BTF type dumping

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Message-ID: <20200930212907.mzg3g5522x3oobco@ast-mbp.dhcp.thefacebook.com>
Date:   Wed, 30 Sep 2020 14:29:07 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 0/4] libbpf: add raw BTF type dumping

On Wed, Sep 30, 2020 at 11:22:50AM -0700, Andrii Nakryiko wrote:
> 
> If you are saying it should emit it in Go format, Rust format, or
> other language-specific way, then sure, 

Yes. that's what I'm saying. cloudflare and cilium are favoring golang.
Hopefully they can adopt skeleton when it's generated in golang.
It would probably mean some support from libbpf and vmlinux.go
Which means BTF dumping in golang.

> maybe, but it sure won't
> re-use C-specific logic of btf_dump__dump_type() as is, because it is
> C language specific. For Go there would be different logic, just as
> for any other language.

sure. that's fine.

> And someone will have to implement it (and
> there would need to be a compelling use case for that, of course). And
> it will be a different API, or at least a generic API with some enum
> specifying "format" (which is the same thing, really, but inferior for
> customizability reasons).

yes. New or reusing api doesn't matter much.
The question is what dumpers libbpf provides.

> But JSON is different from that. It's just a more machine-friendly
> output of textual low-level BTF dump. It could have been BSON or YAML,
> but I hope you don't suggest to emit in those formats as well.

why not. If libbpf does more than one there is no reason to restrict.

> 
> > I don't think that text and json formats bring much value comparing to C,
> > so I would be fine with C only.
> 
> Noted. I disagree and find it very useful all the time, it's pretty
> much the only way I look at BTF. C output is not complete: it doesn't
> show functions, data sections and variables. It's not a replacement
> for raw BTF dump. 

Ok, but it's easy to add dumping of these extra data into vmlinux.h
They can come inside /* */ or as 'extern'.
So C output can be complete and suitable for selftest's strcmp.

> Regardless, feel free to drop patches #2 and #3, but patch #1 fixes
> real issue, so would be nice to land it anyways. Patch #4 adds test
> for changes in patch #1. Let me know if you want me to respin with
> just those 2 patches.

Applied 1 and 4. I was waiting to patchwork bot to notice this partial
application, but looks like it's not that smart... yet.