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Mon, 19 Oct 2026 02:20:25 -0700 (PDT) From: Jakub Sitnicki To: Stanislav Fomichev Cc: Willem Ferguson , netdev@vger.kernel.org, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com, ncardwell@google.com, bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, linux-doc@vger.kernel.org, corbet@lwn.net, linux-kselftest@vger.kernel.org, shuah@kernel.org, linux-kernel@vger.kernel.org, kernel-team@cloudflare.com Subject: Re: [RFC PATCH net-next 0/4] tcp: carry a BPF-chosen identifier in TSval low bits In-Reply-To: (Stanislav Fomichev's message of "Thu, 15 Oct 2026 14:45:02 -0700") References: <20261013103906.2660384-1-wferguson@cloudflare.com> User-Agent: mu4e 1.14.1; emacs 30.2 Date: Mon, 19 Oct 2026 11:20:24 +0200 Message-ID: <87a4oaf3mv.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 Hey Stan, On Thu, Oct 15, 2026 at 02:45 PM -07, Stanislav Fomichev wrote: > On 10/13, Willem Ferguson wrote: [...] >> Questions for reviewers: >> >> 1. Is encoding an identifier in the low bits of TSval acceptable in >> principle, given the trade-offs above? >> 2. If so, what feedback do you have on the implementation? > > Don't see any feedback yet, so from the top of my head: looks like you > control two sides of the communication, so why not a custom (bpf) tcp option? > Would you need that on every packet and it makes it expensive? > > Or any other field you can abuse maybe? IPv6 Flow label? Nah, we don't control the client unfortunately. Client here is any device that connects to our edge PoP. > Implementation-wise, the sock_ops is going away in favor of bpf_tcp_ops, > so BPF_SOCK_OPS_TCP_TS_ID_CB_FLAG is a no go. Yeah, we have just recently realized [1]. Thanks for feedback. [1] https://lore.kernel.org/all/877bjk893u.fsf@cloudflare.com/