netdev - Re: Should I add BPF kfuncs for userspace apps? And how?

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Date: Mon, 18 Dec 2023 11:56:27 -0800
From: Song Liu <song@...nel.org>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Jason Wang <jasowang@...hat.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Jonathan Corbet <corbet@....net>, 
	Willem de Bruijn <willemdebruijn.kernel@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	Yuri Benditovich <yuri.benditovich@...nix.com>, Andrew Melnychenko <andrew@...nix.com>, 
	Benjamin Tissoires <bentiss@...nel.org>, bpf <bpf@...r.kernel.org>, 
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, kvm@...r.kernel.org, 
	LKML <linux-kernel@...r.kernel.org>, virtualization@...ts.linux-foundation.org, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>
Subject: Re: Should I add BPF kfuncs for userspace apps? And how?

Hi Akihiko,

On Tue, Dec 12, 2023 at 12:05 AM Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
>
[...]
> ---
>
> I'm working on a new feature that aids virtio-net implementations using
> tuntap virtual network device. You can see [1] for details, but
> basically it's to extend BPF_PROG_TYPE_SOCKET_FILTER to report four more
> bytes.

AFAICT, [1] adds a new program type, which is really hard to ship. However,
you mentioned it is basically "extend BPF_PROG_TYPE_SOCKET_FILTER to
report four more bytes", which confuses me.

Can we achieve the same goal by extending BPF_PROG_TYPE_SOCKET_FILTER
(without adding a new program type)? Does this require extending
__sk_buff, which
is also not an option any more?

Thanks,
Song