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Miller" , Eric Dumazet , Simon Horman , Michael Chan , Pavan Chebbi , Andrew Lunn , Tony Nguyen , Przemek Kitszel , Saeed Mahameed , Leon Romanovsky , Tariq Toukan , Mark Bloch , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Stanislav Fomichev , intel-wired-lan@lists.osuosl.org, bpf@vger.kernel.org, kernel-team@cloudflare.com, Jesse Brandeburg , Willem Ferguson , Arthur Fabre Subject: Re: [Intel-wired-lan] [PATCH net-next 00/10] Call skb_metadata_set when skb->data points past metadata In-Reply-To: (Jesper Dangaard Brouer's message of "Tue, 13 Jan 2026 19:52:53 +0100") References: <20260110-skb-meta-fixup-skb_metadata_set-calls-v1-0-1047878ed1b0@cloudflare.com> <20260112190856.3ff91f8d@kernel.org> <36deb505-1c82-4339-bb44-f72f9eacb0ac@redhat.com> Date: Tue, 13 Jan 2026 21:22:55 +0100 Message-ID: <87wm1luusg.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Tue, Jan 13, 2026 at 07:52 PM +01, Jesper Dangaard Brouer wrote: > *BUT* this patchset isn't doing that. To me it looks like a cleanup > patchset that simply makes it consistent when skb_metadata_set() called. > Selling it as a pre-requirement for doing copy later seems fishy. Fair point on the framing. The interface cleanup is useful on its own - I should have presented it that way rather than tying it to future work. > Instead of blindly copying XDP data_meta area into a single SKB > extension. What if we make it the responsibility of the TC-ingress BPF- > hook to understand the data_meta format and via (kfunc) helpers > transfer/create the SKB extension that it deems relevant. > Would this be an acceptable approach that makes it easier to propagate > metadata deeper in netstack? I think you and Jakub are actually proposing the same thing. If we can access a buffer tied to an skb extension from BPF, this could act as skb-local storage and solves the problem (with some operational overhead to set up TC on ingress). I'd also like to get Alexei's take on this. We had a discussion before about not wanting to maintain two different storage areas for skb metadata. That was one of two reasons why we abandoned Arthur's patches and why I tried to make the existing headroom-backed metadata area work. But perhaps I misunderstood the earlier discussion. Alexei's point may have been that we don't want another *headroom-backed* metadata area accessible from XDP, because we already have that. Looks like we have two options on the table: Option A) Headroom-backed metadata - Use existing skb metadata area - Patch skb_push/pull call sites to preserve it Option B) Extension-backed metadata - Store metadata in skb extension from BPF - TC BPF copies/extracts what it needs from headroom-metadata Or is there an Option C I'm missing? Thanks, -jkbs