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([2a01:e0a:e17:9700:3f7b:7276:a343:d339]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48862731429sm2278905f8f.5.2026.09.22.00.30.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Sep 2026 00:30:02 -0700 (PDT) Message-ID: Date: Tue, 22 Sep 2026 09:29:58 +0200 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next 6/7] bpf: tcp: Add kfunc to adjust sk->sk_rcvlowat. To: Kuniyuki Iwashima , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi Cc: Yonghong Song , John Fastabend , Stanislav Fomichev , Eric Dumazet , Neal Cardwell , Willem de Bruijn , Tenzin Ukyab , Kuniyuki Iwashima , bpf@vger.kernel.org, netdev@vger.kernel.org References: <20260920195633.3033620-1-kuniyu@google.com> <20260920195633.3033620-7-kuniyu@google.com> Content-Language: en-US From: =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= In-Reply-To: <20260920195633.3033620-7-kuniyu@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Proofpoint-ORIG-GUID: ldA8CYy06sdVQUAi8jYjRjQv6s-b_kIg X-Authority-Analysis: v=2.4 cv=SKnXx+vH c=1 sm=1 tr=0 ts=6ab22e7d cx=c_pps a=I6ewnrIBtnKHmb6SxpX7Vg==:117 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=M51BFTxLslgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=7x6HtfJdh03M6CCDgxCd:22 a=xtH7KyWI9dI7BmFOsl-x:22 a=1XWaLZrsAAAA:8 a=VabnemYjAAAA:8 a=sLGjIoZK2OyoYNR-nVkA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=MqNruPmfsT8GavliLQMe:22 a=gKebqoRLp9LExxC7YDUY:22 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTIyMDEwNiBTYWx0ZWRfX7KM4eCadjlnE DoqvLQEa+Z7M0pDLeAWl9MYKpthOvppxDg2uo/XsCMqJNoAwKxMRHt25yhta1AakPVtkTc1r5FH D2aoC1gOtC7qK32F8Onq53w6c3ZtO8k= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTIyMDEwNiBTYWx0ZWRfX0ByzgFouTrP7 Hrfe9mnaYINenmLMyA7pHGgU4fe1uMItTdYawkJjZyEDwVL3eYlier2rrOR/wyWhdSMvEuMwj6U PiiP4fBqoN0ZcjM2Dbv6iUjQxYWzeTGMOYN7BQypDP136zSWSDvwoF8qEwSEwfqMbhmwOVRpRNN +PpxyIOC+vylESI17yfytCBP9Qh/KlAUg9pC7SlZ/GyCO3MXWi0yJs1dR0V4soOEIS7RQ/3qXct n095d59gxvZY2xFkOBN8331yq7uJywSwAGV22GytdKiSxb0uP5S8jkYg0nx3dzq/clNgNwhOz/D hBbR2qPf97Ie2AGz+HBKeDtVFRyVDX0cMDFjefSjlL9mN/piAIHomQJdw0RLGjiD03WykwxEnFb CFvClkCQYiYDbLvvG0SzFisOwacP3l718RbfT97zU7fLgrU9dgisP1he0Tm8wlQ5Xrp69jnZDqk uOYmWraGPr+KnxVEYiw== X-Proofpoint-GUID: ldA8CYy06sdVQUAi8jYjRjQv6s-b_kIg X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-21_07,2026-09-21_02,2025-10-01_01 On 9/20/26 21:56, Kuniyuki Iwashima wrote: > >=20 > bpf_tcp_ops.{enqueue,dequeue}_rcvq() were added to parse skb and > adjust sk->sk_rcvlowat dynamically to suppress unnecessary wakeups. >=20 > Let's add a new kfunc to set sk->sk_rcvlowat. >=20 > Negative values are clamped to INT_MAX, consistent with SO_RCVLOWAT. >=20 > For enqueue_rcvq(), wakeup is set to false because: >=20 > * tcp_data_ready() is always called after the hooks in > tcp_queue_rcv() and tcp_ofo_queue(). >=20 > * when tcp_fastopen_add_skb() is called for TFO SYN, the socket is > not yet accept()ed, and when called for TFO SYN+ACK, the socket > is woken up by sk->sk_state_change() anyway. >=20 > For dequeue_rcvq(), wakeup is set to true because tcp_data_ready() > is not called in that path. >=20 > An alternative would be to support bpf_setsockopt() for these > hooks. >=20 > However, that approach involves excessive conditionals and an > unnecessary memcpy(), costs we do not want to pay for every skb > in the TCP fast path. >=20 > Signed-off-by: Kuniyuki Iwashima > --- > net/ipv4/bpf_tcp_ops.c | 56 +++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 55 insertions(+), 1 deletion(-) >=20 > diff --git a/net/ipv4/bpf_tcp_ops.c b/net/ipv4/bpf_tcp_ops.c > index b0e14b54917e..3768b1440eb7 100644 > --- a/net/ipv4/bpf_tcp_ops.c > +++ b/net/ipv4/bpf_tcp_ops.c > @@ -359,8 +359,62 @@ static struct bpf_struct_ops bpf_tcp_ops =3D { > .owner =3D THIS_MODULE, > }; > =20 > +__bpf_kfunc_start_defs(); > + > +__bpf_kfunc int bpf_tcp_ops_set_rcvlowat(struct sock *sk, int rcvlowat, > + const struct bpf_prog_aux *aux) > +{ > + u32 moff =3D aux->attach_st_ops_member_off; > + bool wakeup =3D false; > + > + if (moff =3D=3D offsetof(struct bpf_tcp_ops, dequeue_rcvq)) > + wakeup =3D true; > + > + if (rcvlowat < 0) > + rcvlowat =3D INT_MAX; > + > + return __tcp_set_rcvlowat(sk, rcvlowat, wakeup); > +} > + > +__bpf_kfunc_end_defs(); > + > +BTF_KFUNCS_START(bpf_tcp_ops_rcvlowat_kfunc_set) > +BTF_ID_FLAGS(func, bpf_tcp_ops_set_rcvlowat, KF_IMPLICIT_ARGS) > +BTF_KFUNCS_END(bpf_tcp_ops_rcvlowat_kfunc_set) > + > +static int bpf_tcp_ops_rcvlowat_kfunc_filter(const struct bpf_prog *prog, > + u32 kfunc_id) > +{ > + u32 moff; > + > + if (!btf_id_set8_contains(&bpf_tcp_ops_rcvlowat_kfunc_set, kfunc_id)) > + return 0; > + > + if (prog->aux->st_ops !=3D &bpf_tcp_ops) > + return -EACCES; > + > + moff =3D prog->aux->attach_st_ops_member_off; > + if (moff !=3D offsetof(struct bpf_tcp_ops, enqueue_rcvq) && > + moff !=3D offsetof(struct bpf_tcp_ops, dequeue_rcvq)) > + return -EACCES; > + > + return 0; > +} > + > +static const struct btf_kfunc_id_set bpf_tcp_ops_rcvlowat_kfunc_id_set = =3D { > + .owner =3D THIS_MODULE, > + .set =3D &bpf_tcp_ops_rcvlowat_kfunc_set, > + .filter =3D bpf_tcp_ops_rcvlowat_kfunc_filter, > +}; > + > static int __init __bpf_tcp_ops_init(void) > { > - return register_bpf_struct_ops(&bpf_tcp_ops, bpf_tcp_ops); > + int ret; > + > + ret =3D register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, > + &bpf_tcp_ops_rcvlowat_kfunc_id_set); > + ret =3D ret ?: register_bpf_struct_ops(&bpf_tcp_ops, bpf_tcp_ops); > + > + return ret; > } > late_initcall(__bpf_tcp_ops_init); Hi Kuniyuki, Tested-by: Cl=C3=A9ment L=C3=A9ger Thanks, Cl=C3=A9ment