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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 1874BC32750 for ; Tue, 13 Aug 2019 14:46:55 +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 E11A420651 for ; Tue, 13 Aug 2019 14:46:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E11A420651 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]:53006 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hxY4c-0006S1-5J for qemu-devel@archiver.kernel.org; Tue, 13 Aug 2019 10:46:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42304) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hxY4C-00060F-Pq for qemu-devel@nongnu.org; Tue, 13 Aug 2019 10:46:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hxY4B-0006TG-Dv for qemu-devel@nongnu.org; Tue, 13 Aug 2019 10:46:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33694) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hxY48-0006SB-GT; Tue, 13 Aug 2019 10:46:24 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BA8B4307D848; Tue, 13 Aug 2019 14:46:23 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.40.205.136]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 52B707FB8C; Tue, 13 Aug 2019 14:46:22 +0000 (UTC) To: Kevin Wolf , Vladimir Sementsov-Ogievskiy References: <20190812181146.26121-1-vsementsov@virtuozzo.com> <20190812181146.26121-2-vsementsov@virtuozzo.com> <20190813110428.GE4663@localhost.localdomain> <7fcab62a-ad7b-4105-7a23-76c46d8cee0f@virtuozzo.com> <20190813120112.GH4663@localhost.localdomain> <20190813132150.GI4663@localhost.localdomain> From: Max Reitz Openpgp: preference=signencrypt Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <6c666a03-e679-c566-e309-5472a2bbef3f@redhat.com> Date: Tue, 13 Aug 2019 16:46:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190813132150.GI4663@localhost.localdomain> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="JEuZoX91LkbmZWfOMGkq3wlLmALoRyVgr" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Tue, 13 Aug 2019 14:46:23 +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 1/2] block/raw-format: switch to BDRV_BLOCK_DATA with BDRV_BLOCK_RECURSE 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: Denis Lunev , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" 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) --JEuZoX91LkbmZWfOMGkq3wlLmALoRyVgr Content-Type: multipart/mixed; boundary="DqEnOkyNnkPUadNoi0DcxqGlBtfF7mPrE"; protected-headers="v1" From: Max Reitz To: Kevin Wolf , Vladimir Sementsov-Ogievskiy Cc: Denis Lunev , "qemu-devel@nongnu.org" , "qemu-block@nongnu.org" Message-ID: <6c666a03-e679-c566-e309-5472a2bbef3f@redhat.com> Subject: Re: [Qemu-block] [PATCH 1/2] block/raw-format: switch to BDRV_BLOCK_DATA with BDRV_BLOCK_RECURSE References: <20190812181146.26121-1-vsementsov@virtuozzo.com> <20190812181146.26121-2-vsementsov@virtuozzo.com> <20190813110428.GE4663@localhost.localdomain> <7fcab62a-ad7b-4105-7a23-76c46d8cee0f@virtuozzo.com> <20190813120112.GH4663@localhost.localdomain> <20190813132150.GI4663@localhost.localdomain> In-Reply-To: <20190813132150.GI4663@localhost.localdomain> --DqEnOkyNnkPUadNoi0DcxqGlBtfF7mPrE Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 13.08.19 15:21, Kevin Wolf wrote: > Am 13.08.2019 um 14:01 hat Kevin Wolf geschrieben: >> Am 13.08.2019 um 13:28 hat Vladimir Sementsov-Ogievskiy geschrieben: >>> 13.08.2019 14:04, Kevin Wolf wrote: >>>> Am 12.08.2019 um 20:11 hat Vladimir Sementsov-Ogievskiy geschrieben:= >>>>> BDRV_BLOCK_RAW makes generic bdrv_co_block_status to fallthrough to= >>>>> returned file. But is it correct behavior at all? If returned file >>>>> itself has a backing file, we may report as totally unallocated and= >>>>> area which actually has data in bottom backing file. >>>>> >>>>> So, mirroring of qcow2 under raw-format is broken. Which is illustr= ated >>>>> by following commit with a test. Let's make raw-format behave more >>>>> correctly returning BDRV_BLOCK_DATA. >>>>> >>>>> Suggested-by: Max Reitz >>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy >>>> >>>> After some reading, I think I came to the conclusion that RAW is the= >>>> correct thing to do. There is indeed a problem, but this patch is tr= ying >>>> to fix it in the wrong place. >>>> >>>> In the case where the backing file contains some data, and we have a= >>>> 'raw' node above the qcow2 overlay node, the content of the respecti= ve >>>> block is not defined by the queried backing file layer, so it is >>>> completely correct that bdrv_is_allocated() returns false, like it w= ould >>>> if you queried the qcow2 layer directly. If it returned true, we wou= ld >>>> copy everything, which isn't right either (the test cases should may= add >>>> the qemu-img map output of the target so this becomes visible). >>>> >>>> The problem is that we try to recurse along the backing chain, but w= e >>>> fail to make the step from the raw node to the backing file. >>> >>> I'd say, the problem is that we ignore backing chain of non-backing >>> child >> >> Yes, exactly. And I know even less about what happens if a child is >> neither bs->file nor bs->backing. Imagine a qcow2 image with an extern= al >> data file that is a qcow2 image with a backing file itself. :-) >> >> Actually, just having two qcow2 layers nested with bs->file probably >> already fails. >> >>>> Note that just extending Max's "deal with filters" is not enough to = fix >>>> this because raw doesn't actually meet all of the criteria for being= a >>>> filter in this sense (at least because the 'offset' option can chang= e >>>> offsets between raw and its child). >>>> >>>> I think this is essentially a result of special-casing backing files= >>>> everywhere instead of treating them like children like any other. >>> >>> But we need to special-case them, as we have interfaces operating on >>> backing chain, >> >> I'm not sure yet if this means that these interfaces are wrong, but it= >> might. But in any case, I think we depend on special-casing in more >> places than we should. >> >>>> bdrv_co_block_status_above() probably shouldn't recurse along the >>>> backing chain, but along the returned *file pointers, and consider t= he >>>> returned offset in *map. >>> >>> So, you mean that in case of unallocated, format layer should return >>> it's backing file as file? >> >> Yes, because that's where it's reading the data from. >> >> Hm... Now I wonder what this means for DATA... In theory it would have= >> to be set for backing files, but that would make it completely useless= =2E >> We can distinguish the cases by looking at *file, but how does the >> generic block layer know which child should be counted as "allocated" >> and which shouldn't? >=20 > Possible answer to my own question: >=20 > bdrv_is_allocated(bs) isn't even asking a complete question. What we > really need to ask is whether a specific child is where data comes from= =2E >=20 > What the current callers of bdrv_is_allocated() are interested in is > whether the data comes from bs->backing or from somewhere else. That is= , > if removing bs from the graph (so that all parents of bs would point to= > bs->backing instead) would still result in the same data in the given > block. Maybe callers of bdrv_is_allocated() should just ensure that the node they pass actually has a backing file. (If it doesn=E2=80=99t, they should skip all filters until it does.) Max --DqEnOkyNnkPUadNoi0DcxqGlBtfF7mPrE-- --JEuZoX91LkbmZWfOMGkq3wlLmALoRyVgr Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl1SzTwACgkQ9AfbAGHV z0As2AgAlIqPUOBASETBROrYYEMldjlsXr9NNPAJ+nvo5FkQ/hVJDDa6w+iQCzrr 86KADQpetrWsBM5FCsdWxc7iErVwIcVHXVigtrQ5Ezhb7NL1A5HyLCeea0S+BgtH q2LDMpWbR67rP9FisZY3AjfiFx1aAJO8BjfoqIbXvqABJPZFCpG6I0z7pomi2Jf+ n03L41ZE4wBXB2xjDT73ed9IYMtLkif5AffWzEWzT5+EatbfPOXROsMT02vaK2g3 BEis3fYfiQWm6Nhu76eV2nzDD8g45sn8lil7qrdgjVXUpRUHQrx35i7vvBPeaH3a uqhcsYyAcSmGhJh8Jo4kRCivF7FUJQ== =NQ+c -----END PGP SIGNATURE----- --JEuZoX91LkbmZWfOMGkq3wlLmALoRyVgr--