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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A26C8C3A589 for ; Thu, 15 Aug 2019 21:55:15 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4BA222083B for ; Thu, 15 Aug 2019 21:55:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4BA222083B 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 ([::1]:47528 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1hyNiE-0000SR-Bp for qemu-devel@archiver.kernel.org; Thu, 15 Aug 2019 17:55:14 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34388) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1hyNhP-0008DZ-0y for qemu-devel@nongnu.org; Thu, 15 Aug 2019 17:54:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hyNhN-0006IO-Sy for qemu-devel@nongnu.org; Thu, 15 Aug 2019 17:54:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40572) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hyNhL-0006GN-3v; Thu, 15 Aug 2019 17:54:19 -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 2071B8535C; Thu, 15 Aug 2019 21:54:18 +0000 (UTC) Received: from [10.3.117.22] (ovpn-117-22.phx2.redhat.com [10.3.117.22]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0667C8CFA1; Thu, 15 Aug 2019 21:54:14 +0000 (UTC) To: John Snow , qemu-devel@nongnu.org References: <20190815185024.7010-1-eblake@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: <5dbb9c0d-4eb0-b6a0-ff23-107010fa3c1f@redhat.com> Date: Thu, 15 Aug 2019 16:54:13 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="RMLcDIb4TDhgC0QcTqtXfaP3YpWxz9vhp" 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 [10.5.110.25]); Thu, 15 Aug 2019 21:54:18 +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 Subject: Re: [Qemu-devel] [Qemu-block] [PATCH] nbd: Advertise multi-conn for shared read-only connections X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , vsementsov@virtuozzo.com, "open list:Network Block Dev..." , Max Reitz 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) --RMLcDIb4TDhgC0QcTqtXfaP3YpWxz9vhp Content-Type: multipart/mixed; boundary="7Foj4veazXTznhuHrU540y7y8bFvrI6Su"; protected-headers="v1" From: Eric Blake To: John Snow , qemu-devel@nongnu.org Cc: Kevin Wolf , vsementsov@virtuozzo.com, "open list:Network Block Dev..." , Max Reitz Message-ID: <5dbb9c0d-4eb0-b6a0-ff23-107010fa3c1f@redhat.com> Subject: Re: [Qemu-block] [PATCH] nbd: Advertise multi-conn for shared read-only connections References: <20190815185024.7010-1-eblake@redhat.com> In-Reply-To: --7Foj4veazXTznhuHrU540y7y8bFvrI6Su Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 8/15/19 4:45 PM, John Snow wrote: >=20 >=20 > On 8/15/19 2:50 PM, Eric Blake wrote: >> The NBD specification defines NBD_FLAG_CAN_MULTI_CONN, which can be >> advertised when the server promises cache consistency between >> simultaneous clients (basically, rules that determine what FUA and >> flush from one client are able to guarantee for reads from another >> client). When we don't permit simultaneous clients (such as qemu-nbd >> without -e), the bit makes no sense; and for writable images, we >> probably have a lot more work before we can declare that actions from >> one client are cache-consistent with actions from another. But for >> read-only images, where flush isn't changing any data, we might as >> well advertise multi-conn support. What's more, advertisement of the >> bit makes it easier for clients to determine if 'qemu-nbd -e' was in >> use, where a second connection will succeed rather than hang until the= >> first client goes away. >> >> This patch affects qemu as server in advertising the bit. We may want= >> to consider patches to qemu as client to attempt parallel connections >> for higher throughput by spreading the load over those connections >> when a server advertises multi-conn, but for now sticking to one >> connection per nbd:// BDS is okay. >> >> +++ b/blockdev-nbd.c >> @@ -189,7 +189,7 @@ void qmp_nbd_server_add(const char *device, bool h= as_name, const char *name, >> } >> >> exp =3D nbd_export_new(bs, 0, len, name, NULL, bitmap, >> - writable ? 0 : NBD_FLAG_READ_ONLY, >> + writable ? 0 : NBD_FLAG_READ_ONLY, true, >> NULL, false, on_eject_blk, errp); >=20 > Why is it okay to force the share bit on regardless of the value of > 'writable' ? Well, it's probably not, except that... >> @@ -1486,6 +1486,8 @@ NBDExport *nbd_export_new(BlockDriverState *bs, = uint64_t dev_offset, >> perm =3D BLK_PERM_CONSISTENT_READ; >> if ((nbdflags & NBD_FLAG_READ_ONLY) =3D=3D 0) { >> perm |=3D BLK_PERM_WRITE; >> + } else if (shared) { >> + nbdflags |=3D NBD_FLAG_CAN_MULTI_CONN; >> } requesting shared=3Dtrue has no effect for a writable export. I can tweak it for less confusion, though. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org --7Foj4veazXTznhuHrU540y7y8bFvrI6Su-- --RMLcDIb4TDhgC0QcTqtXfaP3YpWxz9vhp Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAl1V1IUACgkQp6FrSiUn Q2qd3Qf/U6o+jGNqBtNKwx9tG0Kllyfc82ePkTr27Q/LBAK8B+C1GpguG923g2RF VKEfmL4l6Gmsq+GEgJReM1SuN0L+irsOPkGxWnrJs9iv3kpB8seKcS+Lz+GrheND 8RkuN3WLWwz0gbB+FJuEGBjO4V9BqUgORj+kk6ET+18f8JmcLHLzrwUWOseQWMo2 EPfzbqz+gbaV2GEADgRRTHm8E5GpV+pEKcf0nNsza4L1ePPXFxnSVU8DYOoHcTMC d6mdKFzYgCvlv1452IL5erFGIDIsXidxpQ//S66Ii0ewdpfpcei6VT9B9CWydRJR cT8WrwymjGmd9F3nfHpxDG22hs/DPA== =00Dv -----END PGP SIGNATURE----- --RMLcDIb4TDhgC0QcTqtXfaP3YpWxz9vhp--