From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D2FBC433DB for ; Fri, 29 Jan 2021 23:49:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3220164DF1 for ; Fri, 29 Jan 2021 23:49:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231202AbhA2Xsx convert rfc822-to-8bit (ORCPT ); Fri, 29 Jan 2021 18:48:53 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:51799 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230009AbhA2Xsx (ORCPT ); Fri, 29 Jan 2021 18:48:53 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-174-N513bYxuPoqZK1qa1Axm_A-1; Fri, 29 Jan 2021 23:47:13 +0000 X-MC-Unique: N513bYxuPoqZK1qa1Axm_A-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 29 Jan 2021 23:47:14 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 29 Jan 2021 23:47:14 +0000 From: David Laight To: 'Matthew Wilcox' , Jakub Kicinski CC: Shoaib Rao , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "netdev@vger.kernel.org" , "David S. Miller" , "andy.rudoff@intel.com" Subject: RE: [PATCH] af_unix: Allow Unix sockets to raise SIGURG Thread-Topic: [PATCH] af_unix: Allow Unix sockets to raise SIGURG Thread-Index: AQHW9oaDqv48RJCczk2sHQ3JiT7IG6o/Q1OQ Date: Fri, 29 Jan 2021 23:47:14 +0000 Message-ID: References: <20210122150638.210444-1-willy@infradead.org> <20210125153650.18c84b1a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <23fc3de2-7541-04c9-a56f-4006a7dc773f@oracle.com> <20210129110605.54df8409@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20210129120250.269c366d@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20210129121837.467280fb@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20210129131820.4b97fdeb@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20210129213217.GD308988@casper.infradead.org> In-Reply-To: <20210129213217.GD308988@casper.infradead.org> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org > I'd encourage anyone thinking about "using OOB" to read > https://tools.ietf.org/html/rfc6093 first. Basically, TCP does not > actually provide an OOB mechanism, and frankly Unix sockets shouldn't > try either. OOB data maps much better onto ISO transport 'expedited data' than anything in a bytestream protocol like TCP. There you can send a message (it is message oriented) that isn't subject to normal data flow control. The length is limited (IIRC 32 bytes) and expedited data has its own credit of one, but can overtake (and is expected to overtake) flow control blocked normal data. All TCP provides is a byte sequence number for OOB data. This is just a marker in the bytestream. It really doesn't map onto the socket OOB data data all. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)