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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Neal Cardwell , Kuniyuki Iwashima , David Ahern , Andrii Nakryiko , Eduard Zingerman , Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shuah Khan , Michal Luczaj , Cong Wang , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH bpf-next v9 2/3] bpf, sockmap: Fix FIONREAD for sockmap In-Reply-To: <20260124113314.113584-3-jiayuan.chen@linux.dev> (Jiayuan Chen's message of "Sat, 24 Jan 2026 19:32:44 +0800") References: <20260124113314.113584-1-jiayuan.chen@linux.dev> <20260124113314.113584-3-jiayuan.chen@linux.dev> Date: Mon, 26 Jan 2026 11:53:01 +0100 Message-ID: <87zf60sl0y.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Sat, Jan 24, 2026 at 07:32 PM +08, Jiayuan Chen wrote: > A socket using sockmap has its own independent receive queue: ingress_msg. > This queue may contain data from its own protocol stack or from other > sockets. > > Therefore, for sockmap, relying solely on copied_seq and rcv_nxt to > calculate FIONREAD is not enough. > > This patch adds a new msg_tot_len field in the psock structure to record > the data length in ingress_msg. Additionally, we implement new ioctl > interfaces for TCP and UDP to intercept FIONREAD operations. > > Note that we intentionally do not include sk_receive_queue data in the > FIONREAD result. Data in sk_receive_queue has not yet been processed by > the BPF verdict program, and may be redirected to other sockets or > dropped. Including it would create semantic ambiguity since this data > may never be readable by the user. > > Unix and VSOCK sockets have similar issues, but fixing them is outside > the scope of this patch as it would require more intrusive changes. > > Previous work by John Fastabend made some efforts towards FIONREAD support: > commit e5c6de5fa025 ("bpf, sockmap: Incorrectly handling copied_seq") > Although the current patch is based on the previous work by John Fastabend, > it is acceptable for our Fixes tag to point to the same commit. > > FD1:read() > -- FD1->copied_seq++ > | [read data] > | > [enqueue data] v > [sockmap] -> ingress to self -> ingress_msg queue > FD1 native stack ------> ^ > -- FD1->rcv_nxt++ -> redirect to other | [enqueue data] > | | > | ingress to FD1 > v ^ > ... | [sockmap] > FD2 native stack > > Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()") > Signed-off-by: Jiayuan Chen > --- Thanks, Jiayuan! Reviewed-by: Jakub Sitnicki