netdev - Re: [PATCH v4 bpf-next 05/14] bpf: Remove btf

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Message-ID: <20200628212019.GH2988321@krava>
Date:   Sun, 28 Jun 2020 23:20:19 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Yonghong Song <yhs@...com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Song Liu <songliubraving@...com>,
        Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Wenbo Zhang <ethercflow@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Andrii Nakryiko <andriin@...com>,
        Brendan Gregg <bgregg@...flix.com>,
        Florent Revest <revest@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v4 bpf-next 05/14] bpf: Remove btf_id helpers resolving

On Sun, Jun 28, 2020 at 01:59:54PM -0700, Yonghong Song wrote:

SNIP

> > > 
> > > The corresponding BTF_ID definition here is:
> > >    BTF_ID_LIST(bpf_skb_output_btf_ids)
> > >    BTF_ID(struct, sk_buff)
> > > 
> > > The bpf helper writer needs to ensure proper declarations
> > > of BTF_IDs like the above matching helpers definition.
> > > Support we have arg1 and arg3 as BTF_ID. then the list
> > > definition may be
> > > 
> > >    BTF_ID_LIST(bpf_skb_output_btf_ids)
> > >    BTF_ID(struct, sk_buff)
> > >    BTF_ID(struct, __unused)
> > >    BTF_ID(struct, task_struct)
> > > 
> > > This probably okay, I guess.
> > 
> > right, AFAIK we don't have such case yet, but would be good
> > to be ready and have something like
> > 
> >    BTF_ID(struct, __unused)
> > 
> > maybe adding new type for that will be better:
> > 
> >    BTF_ID(none, unused)
> 
> Maybe we can have a separate macro BTF_ID_UNUSED macro
> which simply adds 4 bytes hole in the .btf_ids* section.

right, we don't need symbols for that

jirka