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Mon, 29 Jun 2020 00:45:48 +0000 Date: Sun, 28 Jun 2020 17:45:45 -0700 From: Martin KaFai Lau To: Eric Dumazet CC: bpf , Alexei Starovoitov , Daniel Borkmann , kernel-team , Lawrence Brakmo , Neal Cardwell , netdev , Yuchung Cheng Subject: Re: [PATCH bpf-next 02/10] tcp: bpf: Parse BPF experimental header option Message-ID: <20200629004545.cpiiowlhgnk527f3@kafai-mbp.dhcp.thefacebook.com> References: <20200626175501.1459961-1-kafai@fb.com> <20200626175514.1460570-1-kafai@fb.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 X-ClientProxiedBy: BYAPR11CA0043.namprd11.prod.outlook.com (2603:10b6:a03:80::20) To CH2PR15MB3573.namprd15.prod.outlook.com (2603:10b6:610:e::28) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from kafai-mbp.dhcp.thefacebook.com (2620:10d:c090:400::5:807c) by BYAPR11CA0043.namprd11.prod.outlook.com (2603:10b6:a03:80::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3131.20 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 7452ce58-6b77-4a35-05de-08d81bc5c39e X-MS-Exchange-CrossTenant-AuthSource: CH2PR15MB3573.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Jun 2020 00:45:47.9604 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: XAqobbyDCHCrQZlIV5YTLYa5n30jNb4ZPz/tfs7PL71J45E+3kMrRmL7jfgaEUBM X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR15MB3653 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687 definitions=2020-06-28_11:2020-06-26,2020-06-28 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 malwarescore=0 cotscore=-2147483648 lowpriorityscore=0 mlxscore=0 clxscore=1015 bulkscore=0 spamscore=0 suspectscore=0 impostorscore=0 priorityscore=1501 adultscore=0 mlxlogscore=994 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006290002 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Sat, Jun 27, 2020 at 10:17:26AM -0700, Eric Dumazet wrote: [ ... ] > It seems strange that we want to add code in TCP stack only to cover a > limited use case (kind 254 and 0xEB9F magic) > > For something like the work Petar Penkov did (to be able to generate > SYNCOOKIES from XDP), we do not go through tcp_parse_options() and BPF > program > would have to implement its own parsing (without having an SKB at > hand), probably calling a helper function, with no > TCP_SKB_CB(skb)->bpf_hdr_opt_off. > > This patch is hard coding a specific option and will prevent anyone > using private option(s) from using this infrastructure in the future, > yet paying the extra overhead. There is a discussion in patch 4 about not limiting this patch set to option kind 254. That will affect the usefulness of bpf_hdr_opt_off. > > TCP_SKB_CB(skb) is tight, I would prefer keeping the space in it for > standard TCP stack features. > > If an optional BPF program needs to re-parse the TCP options to find a > specific option, maybe the extra cost is noise (especially if this is > only for SYN & SYNACK packets) ? > > Thanks