From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:33600) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hLr6b-0004Zw-Nn for qemu-devel@nongnu.org; Wed, 01 May 2019 11:25:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hLr6V-0001Ds-Sk for qemu-devel@nongnu.org; Wed, 01 May 2019 11:25:07 -0400 References: <20181116184324.8093-1-jsnow@redhat.com> <4bc81482-fab6-80dd-f684-4ffde4241dce@virtuozzo.com> From: Eric Blake Message-ID: Date: Wed, 1 May 2019 10:24:36 -0500 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="NZ2bxkoyGL4juIOgvnyHGP1wjlx3mAtbj" Subject: Re: [Qemu-devel] [PATCH] migration/block-dirty-bitmap: Silence coverity CID 1390625 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: John Snow , Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" Cc: Stefan Hajnoczi , Max Reitz This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --NZ2bxkoyGL4juIOgvnyHGP1wjlx3mAtbj From: Eric Blake To: John Snow , Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" Cc: Stefan Hajnoczi , Max Reitz Message-ID: Subject: Re: [Qemu-devel] [PATCH] migration/block-dirty-bitmap: Silence coverity CID 1390625 References: <20181116184324.8093-1-jsnow@redhat.com> <4bc81482-fab6-80dd-f684-4ffde4241dce@virtuozzo.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 4/30/19 6:08 PM, John Snow wrote: >=20 >=20 > On 11/20/18 10:15 AM, Vladimir Sementsov-Ogievskiy wrote: >> 16.11.2018 21:43, John Snow wrote: >>> Coverity warns that backing_bs() could give us a NULL pointer, which >>> we then use without checking that it isn't. >>> >>> In our loop condition, we check bs && bs->drv as a point of habit, bu= t >>> by nature of the block graph, we cannot have null bs pointers here. >>> >>> This loop skips only implicit nodes, which always have children, so >>> this loop should never encounter a null value. >> >=20 > I let this drop again :) >=20 >> You mean, always have backing (not file for ex.)? Should we at least a= dd a comment >> near "bool implicit;" that the node must have backing.. >> >> Do we have filters, using 'file' child instead of backing, will we wan= t to auto insert them, and therefore mark them with implicit=3Dtrue? >> >=20 > I actually have no idea. I guess this is the sort of thing we actually > really want a dedicated kind of API for. "Find first non-filter" seems > like a common use case that we'd want. >=20 > [But maybe I'll avoid this problem.] Max has already tried to tackle that problem: https://lists.gnu.org/archive/html/qemu-devel/2019-04/msg01713.html >=20 >> And one more thing: >> So, it's looks like a wrong way to search for all block-nodes, instead= of looping through backing chain to the first not-implicit bds, we must = recursively explore the whole block graph, to find _all_ the bitmaps. >> >=20 > Looking at this again after not having done so for so long -- I guess > that bdrv_first/bdrv_next only iterate over *top level* BDSes and not > any children thereof. You're right, even the method here isn't quite > correct. We want to find ALL nodes, wherever they are. >=20 > query_named_block_nodes uses an implementation in block.c to accomplish= > this because the API is not public.... or, it wasn't, but it looks like= > we have bdrv_next_all_states now, and we could use this to just find AL= L > of the bdrv nodes. >=20 > Ehm.... let me send something a little more RFC-caliber that should > address your concern (as well as Peter's) here. Max's series also tries to improve how we visit nodes when determining which bitmaps to find. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org --NZ2bxkoyGL4juIOgvnyHGP1wjlx3mAtbj Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAlzJujQACgkQp6FrSiUn Q2rrgwf/Z4xmDq0VHvF3495unToxko7PShHyR5SSiF5FCuN+WV1m3XyDdJNzWawO qzo1XZ+4aTMmSocXBXggY359d0GkgXpMZo+dxuvp2Sqox0Pft34WfkYQz05RlG82 vYW1LMzyAlUmg9SwKTf2YnOBfA2nV7cK+HT26gReCcozifJHz6IMsw6iBqUvihln RBmbM5xTmPuynscwL6EuCw00ngQK9KBDC6oaI2cXoWs1O8qGF4XK5CRY43FbOMXE CiewuU//VoJEJ6k+mkVfzcZAAd1YH+GZGtfrbt/G85TzS+26DjMvMaclX/ONq9PP 3y0xnNVsAvUk9bl8enkZiyNJONXqXA== =0q0G -----END PGP SIGNATURE----- --NZ2bxkoyGL4juIOgvnyHGP1wjlx3mAtbj-- 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=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 F1B21C43219 for ; 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Wed, 01 May 2019 11:25:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38728) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hLr6H-00017L-MS; Wed, 01 May 2019 11:24:50 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 41604308FED4; Wed, 1 May 2019 15:24:47 +0000 (UTC) Received: from [10.3.116.15] (ovpn-116-15.phx2.redhat.com [10.3.116.15]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3EBB37B91F; Wed, 1 May 2019 15:24:37 +0000 (UTC) To: John Snow , Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" References: <20181116184324.8093-1-jsnow@redhat.com> <4bc81482-fab6-80dd-f684-4ffde4241dce@virtuozzo.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: Date: Wed, 1 May 2019 10:24:36 -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="NZ2bxkoyGL4juIOgvnyHGP1wjlx3mAtbj" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Wed, 01 May 2019 15:24:47 +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] migration/block-dirty-bitmap: Silence coverity CID 1390625 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: Stefan Hajnoczi , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Message-ID: <20190501152436.Eed7dmaoQg8JsrMco4uEloDopxyh8eY56OdWwUF_E6o@z> This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --NZ2bxkoyGL4juIOgvnyHGP1wjlx3mAtbj From: Eric Blake To: John Snow , Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" Cc: Stefan Hajnoczi , Max Reitz Message-ID: Subject: Re: [Qemu-devel] [PATCH] migration/block-dirty-bitmap: Silence coverity CID 1390625 References: <20181116184324.8093-1-jsnow@redhat.com> <4bc81482-fab6-80dd-f684-4ffde4241dce@virtuozzo.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 4/30/19 6:08 PM, John Snow wrote: >=20 >=20 > On 11/20/18 10:15 AM, Vladimir Sementsov-Ogievskiy wrote: >> 16.11.2018 21:43, John Snow wrote: >>> Coverity warns that backing_bs() could give us a NULL pointer, which >>> we then use without checking that it isn't. >>> >>> In our loop condition, we check bs && bs->drv as a point of habit, bu= t >>> by nature of the block graph, we cannot have null bs pointers here. >>> >>> This loop skips only implicit nodes, which always have children, so >>> this loop should never encounter a null value. >> >=20 > I let this drop again :) >=20 >> You mean, always have backing (not file for ex.)? Should we at least a= dd a comment >> near "bool implicit;" that the node must have backing.. >> >> Do we have filters, using 'file' child instead of backing, will we wan= t to auto insert them, and therefore mark them with implicit=3Dtrue? >> >=20 > I actually have no idea. I guess this is the sort of thing we actually > really want a dedicated kind of API for. "Find first non-filter" seems > like a common use case that we'd want. >=20 > [But maybe I'll avoid this problem.] Max has already tried to tackle that problem: https://lists.gnu.org/archive/html/qemu-devel/2019-04/msg01713.html >=20 >> And one more thing: >> So, it's looks like a wrong way to search for all block-nodes, instead= of looping through backing chain to the first not-implicit bds, we must = recursively explore the whole block graph, to find _all_ the bitmaps. >> >=20 > Looking at this again after not having done so for so long -- I guess > that bdrv_first/bdrv_next only iterate over *top level* BDSes and not > any children thereof. You're right, even the method here isn't quite > correct. We want to find ALL nodes, wherever they are. >=20 > query_named_block_nodes uses an implementation in block.c to accomplish= > this because the API is not public.... or, it wasn't, but it looks like= > we have bdrv_next_all_states now, and we could use this to just find AL= L > of the bdrv nodes. >=20 > Ehm.... let me send something a little more RFC-caliber that should > address your concern (as well as Peter's) here. Max's series also tries to improve how we visit nodes when determining which bitmaps to find. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org --NZ2bxkoyGL4juIOgvnyHGP1wjlx3mAtbj Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAlzJujQACgkQp6FrSiUn Q2rrgwf/Z4xmDq0VHvF3495unToxko7PShHyR5SSiF5FCuN+WV1m3XyDdJNzWawO qzo1XZ+4aTMmSocXBXggY359d0GkgXpMZo+dxuvp2Sqox0Pft34WfkYQz05RlG82 vYW1LMzyAlUmg9SwKTf2YnOBfA2nV7cK+HT26gReCcozifJHz6IMsw6iBqUvihln RBmbM5xTmPuynscwL6EuCw00ngQK9KBDC6oaI2cXoWs1O8qGF4XK5CRY43FbOMXE CiewuU//VoJEJ6k+mkVfzcZAAd1YH+GZGtfrbt/G85TzS+26DjMvMaclX/ONq9PP 3y0xnNVsAvUk9bl8enkZiyNJONXqXA== =0q0G -----END PGP SIGNATURE----- --NZ2bxkoyGL4juIOgvnyHGP1wjlx3mAtbj--