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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 3955FC28CC5 for ; Wed, 5 Jun 2019 17:14:25 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 02DDD206C3 for ; Wed, 5 Jun 2019 17:14:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 02DDD206C3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:47394 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hYZUW-0008Lk-9I for qemu-devel@archiver.kernel.org; Wed, 05 Jun 2019 13:14:24 -0400 Received: from eggs.gnu.org ([209.51.188.92]:53495) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hYZTJ-0007ef-SE for qemu-devel@nongnu.org; Wed, 05 Jun 2019 13:13:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hYZTI-0006eP-Mq for qemu-devel@nongnu.org; Wed, 05 Jun 2019 13:13:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39468) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hYZTA-0006Ib-Vb; Wed, 05 Jun 2019 13:13:01 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id F16C42CD801; Wed, 5 Jun 2019 17:12:58 +0000 (UTC) Received: from [10.3.116.85] (ovpn-116-85.phx2.redhat.com [10.3.116.85]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 35E5C18E46; Wed, 5 Jun 2019 17:12:58 +0000 (UTC) To: Vladimir Sementsov-Ogievskiy , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <20190605100913.34972-1-vsementsov@virtuozzo.com> <20190605100913.34972-3-vsementsov@virtuozzo.com> <20190605163710.GP8956@redhat.com> From: Eric Blake Openpgp: preference=signencrypt Autocrypt: addr=eblake@redhat.com; keydata= xsBNBEvHyWwBCACw7DwsQIh0kAbUXyqhfiKAKOTVu6OiMGffw2w90Ggrp4bdVKmCaEXlrVLU xphBM8mb+wsFkU+pq9YR621WXo9REYVIl0FxKeQo9dyQBZ/XvmUMka4NOmHtFg74nvkpJFCD TUNzmqfcjdKhfFV0d7P/ixKQeZr2WP1xMcjmAQY5YvQ2lUoHP43m8TtpB1LkjyYBCodd+LkV GmCx2Bop1LSblbvbrOm2bKpZdBPjncRNob73eTpIXEutvEaHH72LzpzksfcKM+M18cyRH+nP sAd98xIbVjm3Jm4k4d5oQyE2HwOur+trk2EcxTgdp17QapuWPwMfhaNq3runaX7x34zhABEB AAHNHkVyaWMgQmxha2UgPGVibGFrZUByZWRoYXQuY29tPsLAegQTAQgAJAIbAwULCQgHAwUV CgkICwUWAgMBAAIeAQIXgAUCS8fL9QIZAQAKCRCnoWtKJSdDahBHCACbl/5FGkUqJ89GAjeX RjpAeJtdKhujir0iS4CMSIng7fCiGZ0fNJCpL5RpViSo03Q7l37ss+No+dJI8KtAp6ID+PMz wTJe5Egtv/KGUKSDvOLYJ9WIIbftEObekP+GBpWP2+KbpADsc7EsNd70sYxExD3liwVJYqLc Rw7so1PEIFp+Ni9A1DrBR5NaJBnno2PHzHPTS9nmZVYm/4I32qkLXOcdX0XElO8VPDoVobG6 gELf4v/vIImdmxLh/w5WctUpBhWWIfQDvSOW2VZDOihm7pzhQodr3QP/GDLfpK6wI7exeu3P pfPtqwa06s1pae3ad13mZGzkBdNKs1HEm8x6zsBNBEvHyWwBCADGkMFzFjmmyqAEn5D+Mt4P zPdO8NatsDw8Qit3Rmzu+kUygxyYbz52ZO40WUu7EgQ5kDTOeRPnTOd7awWDQcl1gGBXgrkR pAlQ0l0ReO57Q0eglFydLMi5bkwYhfY+TwDPMh3aOP5qBXkm4qIYSsxb8A+i00P72AqFb9Q7 3weG/flxSPApLYQE5qWGSXjOkXJv42NGS6o6gd4RmD6Ap5e8ACo1lSMPfTpGzXlt4aRkBfvb NCfNsQikLZzFYDLbQgKBA33BDeV6vNJ9Cj0SgEGOkYyed4I6AbU0kIy1hHAm1r6+sAnEdIKj cHi3xWH/UPrZW5flM8Kqo14OTDkI9EtlABEBAAHCwF8EGAEIAAkFAkvHyWwCGwwACgkQp6Fr SiUnQ2q03wgAmRFGDeXzc58NX0NrDijUu0zx3Lns/qZ9VrkSWbNZBFjpWKaeL1fdVeE4TDGm I5mRRIsStjQzc2R9b+2VBUhlAqY1nAiBDv0Qnt+9cLiuEICeUwlyl42YdwpmY0ELcy5+u6wz mK/jxrYOpzXKDwLq5k4X+hmGuSNWWAN3gHiJqmJZPkhFPUIozZUCeEc76pS/IUN72NfprZmF Dp6/QDjDFtfS39bHSWXKVZUbqaMPqlj/z6Ugk027/3GUjHHr8WkeL1ezWepYDY7WSoXwfoAL 2UXYsMAr/uUncSKlfjvArhsej0S4zbqim2ZY6S8aRWw94J3bSvJR+Nwbs34GPTD4Pg== Organization: Red Hat, Inc. Message-ID: <19a96fc2-7f12-7b30-edef-b3da66eef759@redhat.com> Date: Wed, 5 Jun 2019 12:12:56 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="c8GZ1fG4m8jDVlJI7I51gZljI7JrEkTz9" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Wed, 05 Jun 2019 17:12:59 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 X-Content-Filtered-By: Mailman/MimeDel 2.1.21 Subject: Re: [Qemu-devel] [PATCH 2/2] nbd-client: enable TCP keepalive X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "kwolf@redhat.com" , Denis Lunev , "qemu-devel@nongnu.org" , "qemu-block@nongnu.org" , "mreitz@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --c8GZ1fG4m8jDVlJI7I51gZljI7JrEkTz9 From: Eric Blake To: Vladimir Sementsov-Ogievskiy , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= Cc: "qemu-devel@nongnu.org" , "qemu-block@nongnu.org" , "mreitz@redhat.com" , "kwolf@redhat.com" , Denis Lunev Message-ID: <19a96fc2-7f12-7b30-edef-b3da66eef759@redhat.com> Subject: Re: [PATCH 2/2] nbd-client: enable TCP keepalive References: <20190605100913.34972-1-vsementsov@virtuozzo.com> <20190605100913.34972-3-vsementsov@virtuozzo.com> <20190605163710.GP8956@redhat.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 6/5/19 12:05 PM, Vladimir Sementsov-Ogievskiy wrote: >> By enabling TCP keepalives we are explicitly making the connection >> less reliable by forcing it to be terminated when keepalive >> threshold triggers, instead of waiting longer for TCP to recover. >> >> The rationale s that once a connection has been in a hung state for >> so long that keepalive triggers, its (hopefully) not useful to the >> mgmt app to carry on waiting anyway. >> >> If the connection is terminated by keepalive & the mgmt app then >> spawns a new client to carry on with the work, what are the risks >> involved ? eg Could packets from the stuck, terminated, connection >> suddenly arrive later and trigger I/O with outdated data payload ? >=20 > Hmm, I believe that tcp guarantees isolation between different connecti= ons >=20 >> >> I guess this is no different a situation from an app explicitly >> killing the QEMU NBD client process instead & spawning a new one. >> >> I'm still feeling a little uneasy about enabling it unconditionally >> though, since pretty much everything I know which supports keepalives >> has a way to turn them on/off at least, even if you can't tune the >> individual timer settings. >=20 > Hm. So, I can add bool keepalive parameter for nbd format with default = to true. > And if needed, it may be later extended to be qapi 'alternate' of bool = or struct with > three numeric parameters, corresponding to TCP_KEEPCNT, TCP_KEEPIDLE an= d TCP_KEEPINTVL . >=20 > Opinions? Adding a bool that could later turn into a qapi 'alternate' for fine-tuning seems reasonable. Defaulting the bool to true is not backwards-compatible; better would be defaulting it to false and letting users opt-in; introspection will also work to let you know whether the feature is present. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org --c8GZ1fG4m8jDVlJI7I51gZljI7JrEkTz9 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAlz3+BgACgkQp6FrSiUn Q2oLGAf/VHL4MkMKRaV6pNUil5qq6jkItgk3Ls3il0xhydOrzz3G12DY9K1pzHuK 9R+Cq+Wj8bGSKb62Dfmakzu9EGoyx/yFZIJOCbTjUn0MKvcBMMkjvCxHr2Z2IyjW ZDZb/efhjLf8ZGQFKOGDeCR4wZU/RyxL0JQstHK//uTMtrXf+ieb4ZSHybHMUuk1 3rEXYYsSTFh3dxN3746jZz1gfJltpsMJMJdF86VvsOXPUjJz5PYKxUtDtw/PlLpt UF8RoZxv2bt3thdjCZsTMZLjWDgqZVZ3WNmzWaD0mUcNfDzzw2KCKEKgkY+aYti9 cwxaUw1zU22aR0Zy9xvFoZTL/ZBgPg== =MX4O -----END PGP SIGNATURE----- --c8GZ1fG4m8jDVlJI7I51gZljI7JrEkTz9--