netdev - Re: [RFC PATCH 1/7] net: skbuff: Add tun_vnet

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Date: Sun, 8 Oct 2023 20:39:07 +0200
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Jason Wang <jasowang@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org, 
	bpf@...r.kernel.org, davem@...emloft.net, kuba@...nel.org, ast@...nel.org, 
	daniel@...earbox.net, andrii@...nel.org, kafai@...com, songliubraving@...com, 
	yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org, 
	rdunlap@...radead.org, willemb@...gle.com, gustavoars@...nel.org, 
	herbert@...dor.apana.org.au, steffen.klassert@...unet.com, nogikh@...gle.com, 
	pablo@...filter.org, decui@...rosoft.com, cai@....pw, jakub@...udflare.com, 
	elver@...gle.com, pabeni@...hat.com, 
	Yuri Benditovich <yuri.benditovich@...nix.com>
Subject: Re: [RFC PATCH 1/7] net: skbuff: Add tun_vnet_hash flag

On Sun, Oct 8, 2023 at 7:22 AM Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
>
> tun_vnet_hash can use this flag to indicate it stored virtio-net hash
> cache to cb.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
>  include/linux/skbuff.h | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 4174c4b82d13..e638f157c13c 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -837,6 +837,7 @@ typedef unsigned char *sk_buff_data_t;
>   *     @truesize: Buffer size
>   *     @users: User count - see {datagram,tcp}.c
>   *     @extensions: allocated extensions, valid if active_extensions is nonzero
> + *     @tun_vnet_hash: tun stored virtio-net hash cache to cb
>   */
>
>  struct sk_buff {
> @@ -989,6 +990,7 @@ struct sk_buff {
>  #if IS_ENABLED(CONFIG_IP_SCTP)
>         __u8                    csum_not_inet:1;
>  #endif
> +       __u8                    tun_vnet_hash:1;

sk_buff space is very limited.

No need to extend it, especially for code that stays within a single
subsystem (tun).

To a lesser extent the same point applies to the qdisc_skb_cb.