netdev - Re: [PATCH bpf-next v2 01/13] bpf: Add dynptr type for skb metadata

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Message-ID: <9aa1f2b0-0f63-45e8-b787-e14d53cac75a@linux.dev>
Date: Thu, 17 Jul 2025 17:06:21 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jakub Sitnicki <jakub@...udflare.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 Arthur Fabre <arthur@...hurfabre.com>, Daniel Borkmann
 <daniel@...earbox.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
 Jesse Brandeburg <jbrandeburg@...udflare.com>,
 Joanne Koong <joannelkoong@...il.com>, Lorenzo Bianconi
 <lorenzo@...nel.org>, Toke Høiland-Jørgensen
 <thoiland@...hat.com>, Yan Zhai <yan@...udflare.com>,
 kernel-team@...udflare.com, netdev@...r.kernel.org,
 Stanislav Fomichev <sdf@...ichev.me>, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 01/13] bpf: Add dynptr type for skb metadata

On 7/16/25 9:16 AM, Jakub Sitnicki wrote:
> +__bpf_kfunc int bpf_dynptr_from_skb_meta(struct __sk_buff *skb, u64 flags,
> +					 struct bpf_dynptr *ptr__uninit)
> +{
> +	return dynptr_from_skb_meta(skb, flags, ptr__uninit, false);
> +}
> +
>   __bpf_kfunc int bpf_dynptr_from_xdp(struct xdp_md *x, u64 flags,
>   				    struct bpf_dynptr *ptr__uninit)
>   {
> @@ -12165,8 +12190,15 @@ int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
>   	return 0;
>   }
>   
> +int bpf_dynptr_from_skb_meta_rdonly(struct __sk_buff *skb, u64 flags,
> +				    struct bpf_dynptr *ptr__uninit)
> +{
> +	return dynptr_from_skb_meta(skb, flags, ptr__uninit, true);
> +}
> +
>   BTF_KFUNCS_START(bpf_kfunc_check_set_skb)
>   BTF_ID_FLAGS(func, bpf_dynptr_from_skb, KF_TRUSTED_ARGS)
> +BTF_ID_FLAGS(func, bpf_dynptr_from_skb_meta, KF_TRUSTED_ARGS)

I looked at the high level of the set. I have a quick question.

Have you considered to create another bpf_kfunc_check_set_xxx that is only for 
the tc and tracing prog type? No need to expose this kfunc to other prog types 
if the skb_meta is not available now at those hooks.

It seems patch 5 is to ensure other prog types has meta_len 0 and some of the 
tests are to ensure that the other prog types cannot do useful things with the 
new skb_meta kfunc. The tests will also be different eventually when the 
skb_meta can be preserved beyond tc.