netdev - Re: [PATCH bpf-next v4 2/8] bpf: Enable read/write access to skb metadata through a dynptr

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Message-ID: <20250723173038.45cbaf01@kernel.org>
Date: Wed, 23 Jul 2025 17:30:38 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Jakub Sitnicki <jakub@...udflare.com>
Cc: bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>, Andrii
 Nakryiko <andrii@...nel.org>, Arthur Fabre <arthur@...hurfabre.com>, Daniel
 Borkmann <daniel@...earbox.net>, Eduard Zingerman <eddyz87@...il.com>, Eric
 Dumazet <edumazet@...gle.com>, Jesper Dangaard Brouer <hawk@...nel.org>,
 Jesse Brandeburg <jbrandeburg@...udflare.com>, Joanne Koong
 <joannelkoong@...il.com>, Lorenzo Bianconi <lorenzo@...nel.org>, Martin
 KaFai Lau <martin.lau@...ux.dev>, Toke Høiland-Jørgensen <thoiland@...hat.com>, Yan Zhai <yan@...udflare.com>,
 kernel-team@...udflare.com, netdev@...r.kernel.org, Stanislav Fomichev
 <sdf@...ichev.me>
Subject: Re: [PATCH bpf-next v4 2/8] bpf: Enable read/write access to skb
 metadata through a dynptr

On Wed, 23 Jul 2025 19:36:47 +0200 Jakub Sitnicki wrote:
> Now that we can create a dynptr to skb metadata, make reads to the metadata
> area possible with bpf_dynptr_read() or through a bpf_dynptr_slice(), and
> make writes to the metadata area possible with bpf_dynptr_write() or
> through a bpf_dynptr_slice_rdwr().

What are the expectations around the writes? Presumably we could have
two programs writing into the same metadata if the SKB is a clone, no?