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,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 DD5CBC76186 for ; Wed, 17 Jul 2019 08:37:59 +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 B48962173E for ; Wed, 17 Jul 2019 08:37:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B48962173E 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]:55084 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnfRn-00062P-0r for qemu-devel@archiver.kernel.org; Wed, 17 Jul 2019 04:37:59 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48097) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnfRY-0005JD-Sw for qemu-devel@nongnu.org; Wed, 17 Jul 2019 04:37:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hnfRX-0001MA-SD for qemu-devel@nongnu.org; Wed, 17 Jul 2019 04:37:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40684) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hnfRV-0001HT-DL; Wed, 17 Jul 2019 04:37:41 -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 AB9ACC057EC0; Wed, 17 Jul 2019 08:37:40 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.40.205.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 99EA25D968; Wed, 17 Jul 2019 08:37:38 +0000 (UTC) To: Kevin Wolf References: <20190715104508.7568-1-mreitz@redhat.com> <20190715104508.7568-2-mreitz@redhat.com> <20190716165459.GI7297@linux.fritz.box> 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: Date: Wed, 17 Jul 2019 10:37:36 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190716165459.GI7297@linux.fritz.box> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="fJss0t3B5iJRoP98X6yzdQ3y9RWMOHTgH" 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 [10.5.110.32]); Wed, 17 Jul 2019 08:37:40 +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] [PATCH for-4.1? 1/4] qcow2: Fix .bdrv_has_zero_init() 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: Jeff Cody , Stefan Weil , qemu-devel@nongnu.org, qemu-block@nongnu.org, Stefano Garzarella 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) --fJss0t3B5iJRoP98X6yzdQ3y9RWMOHTgH Content-Type: multipart/mixed; boundary="u3GSwk9gZjxsdxtvjnho51fP3KSQy9cBN"; protected-headers="v1" From: Max Reitz To: Kevin Wolf Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Stefano Garzarella , Stefan Weil , Jeff Cody Message-ID: Subject: Re: [PATCH for-4.1? 1/4] qcow2: Fix .bdrv_has_zero_init() References: <20190715104508.7568-1-mreitz@redhat.com> <20190715104508.7568-2-mreitz@redhat.com> <20190716165459.GI7297@linux.fritz.box> In-Reply-To: <20190716165459.GI7297@linux.fritz.box> --u3GSwk9gZjxsdxtvjnho51fP3KSQy9cBN Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 16.07.19 18:54, Kevin Wolf wrote: > Am 15.07.2019 um 12:45 hat Max Reitz geschrieben: >> If a qcow2 file is preallocated, it can no longer guarantee that it >> initially appears as filled with zeroes. >> >> So implement .bdrv_has_zero_init() by checking whether the file is >> preallocated; if so, forward the call to the underlying storage node, >> except for when it is encrypted: Encrypted preallocated images always >> return effectively random data, so .bdrv_has_zero_init() must always >> return 0 for them. >> >> Reported-by: Stefano Garzarella >> Signed-off-by: Max Reitz >=20 > Hm... This patch only really works directly after image creation (which= > is indeed where .bdrv_has_zero_init is used). Why do we have to have a > full qcow2_is_zero() that loops over the whole image just to find out > whether it's preallocated? Wouldn't looking at a single data cluster be= > enough? Hm. I would like to agree (because you=E2=80=99re right), but now I see = that the callers of bdrv_has_zero_init() don=E2=80=99t necessarily hold to tha= t convention. For example, qemu-img convert has the -n flag, but that doesn=E2=80=99t s= top it from invoking bdrv_has_zero_init(). Which is a bug, of course. $ ./qemu-img create -f qcow2 src.qcow2 64M $ ./qemu-img create -f qcow2 dest.qcow2 64M $ ./qemu-io -c 'write -P 42 0 64M' dest.qcow2 $ ./qemu-img convert -n src.qcow2 dest.qcow2 $ ./qemu-img compare src.qcow2 dest.qcow2 Content mismatch at offset 0! Aw, man, why does this keep happening... :-/ OK, so qemu-img convert -n is easy to fix. But there are more callers: mirror: Uses this function to inquire whether it needs to zero the target before actually doing something useful. There is no guarantee that the target is a new image. Well, it just isn=E2=80=99t with mode=3D= existing or blockdev-mirror. parallels: Whether to write zeroes to newly added image areas. That actually sounds correct, because those new areas cannot point to any data yet. Well, maybe not correct, because bdrv_has_zero_init() is not the same as =E2=80=9Cwhen this image grows, new areas will be zero=E2=80=9D, but at l= east bdrv_hsa_zero_init() will return false if the the latter is false. vhdx: Similarly to parallels, it uses this information to check whether it needs to zero new areas when growing an image file. raw/vmdk/vpc: Just passing through info from their storage child. Hm, OK. So mirror and qemu-img need fixing. That sounds possible. Max --u3GSwk9gZjxsdxtvjnho51fP3KSQy9cBN-- --fJss0t3B5iJRoP98X6yzdQ3y9RWMOHTgH Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl0u3lAACgkQ9AfbAGHV z0Bi9wf/em74qJbEvq8QX5SBt+7OL2IE0wnzNtKu0a44UuIpAdhewj9XsakBKm8S Rkn2j4/qO/xn5UGSNxooGSSxaPDoM78cUhGLVFyj3qD/WLv4dth6XpTHF7yNVv+b y0r8UBlWG6BEOSYuydvfrjN1rYV46b8oNUzpVO9iLoq8pCPCBcCfRwQlxmijoZi7 1Wt/YnkBrbcn7L3hirjFXrPtMLkbSYE7c2iXPmb0UnfJp41JqZQprh3hT5frUkar TawAKvfREx1Z297fPiAhM+mOF7tQJtXHFE72mLMVEwYPqFh9OHEoHR7CGKiHq1cy fhQVrym8cTnDZPGn/M27ppW5GDNfzw== =Lxv7 -----END PGP SIGNATURE----- --fJss0t3B5iJRoP98X6yzdQ3y9RWMOHTgH--