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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 61DEFC33CB1 for ; Thu, 16 Jan 2020 15:07:50 +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 29F3720730 for ; Thu, 16 Jan 2020 15:07:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="N74ehRqh" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 29F3720730 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]:43612 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1is6kP-0006RK-1z for qemu-devel@archiver.kernel.org; Thu, 16 Jan 2020 10:07:49 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:58171) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1is6gl-0002NV-0I for qemu-devel@nongnu.org; Thu, 16 Jan 2020 10:04:06 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1is6gg-0004PP-AN for qemu-devel@nongnu.org; Thu, 16 Jan 2020 10:04:02 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:44215 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1is6gg-0004PA-5d for qemu-devel@nongnu.org; Thu, 16 Jan 2020 10:03:58 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579187037; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=20+cTvTaLmnc2ukRAHPzMlL60khISVae9HSgFglB/0A=; b=N74ehRqhdGGMnLSuM1Dd+/rTO+mP4LtO8VtEnHdUqhzQDHtyD3HDDXxYKvlrlJUJq/hxoB qFXprX1muILNC5JmuRaxPnA3f6rSMR847x/25OyK62nnqbZqLPlN4p3EM4belZLRKm68Kj gJ9Si8hwbHhPp9L5CxFeZnBvDcvMHSI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-249-1etjbdG3MHmaii3yNckCvQ-1; Thu, 16 Jan 2020 10:03:55 -0500 X-MC-Unique: 1etjbdG3MHmaii3yNckCvQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 69B92801E67; Thu, 16 Jan 2020 15:03:54 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-185.ams2.redhat.com [10.36.117.185]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DA8BF60E3E; Thu, 16 Jan 2020 15:03:48 +0000 (UTC) Subject: Re: Bug? qemu-img convert to preallocated image makes it sparse To: Eric Blake , "Richard W.M. Jones" , qemu-devel@nongnu.org, qemu-block@nongnu.org, mlevitsk@redhat.com, sgarzare@redhat.com References: <20200116141352.GA32053@redhat.com> <962aa54b-f6e5-bb43-50a0-c4cad59cd22e@redhat.com> <75daaf8f-0bfe-d3f6-5df4-88c29b2d9b07@redhat.com> From: Max Reitz 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: <026ac30d-930c-0c81-0825-346e33e59f36@redhat.com> Date: Thu, 16 Jan 2020 16:03:46 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <75daaf8f-0bfe-d3f6-5df4-88c29b2d9b07@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="azLSSi2pvb7k4AHmq0szb48ikED4nqMnt" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: , 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) --azLSSi2pvb7k4AHmq0szb48ikED4nqMnt Content-Type: multipart/mixed; boundary="eW7H4EzN1u3SAEA1rZRP9qMWiy2nplFMm" --eW7H4EzN1u3SAEA1rZRP9qMWiy2nplFMm Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 16.01.20 15:57, Eric Blake wrote: > On 1/16/20 8:47 AM, Max Reitz wrote: >=20 >> So when you convert to the target image, you have to make sure all areas >> that are zero in the source are zero in the target, too.=C2=A0 The way w= e do >> that is to write zeroes to the target.=C2=A0 The problem is that this >> operation disregards the previous preallocation and discards the >> preallocated space. >> >> As for fixing the bug...=C2=A0 Can we fix it in qemu(-img)? >> >> We could try to detect whether areas that are zero in the source are >> zero in the (preallocated) target image, too.=C2=A0 But doing so what re= quire >> reading the data from those areas and comparing it to zero.=C2=A0 That w= ould >> take time and it isn=E2=80=99t trivial.=C2=A0 So that=E2=80=99s somethin= g I=E2=80=99d rather avoid. >=20 > Can't we also use block status queries on the destination, as that is > likely to be faster than actual reads and comparison to zero? It might work for falloc preallocation, but I don=E2=80=99t know whether we= are really guaranteed that fallocated() areas return holes through lseek(). It won=E2=80=99t work for full preallocation, though. Yes, you might get a= round that with -S 0 then, but I think overall the simplest thing would be a --target-is-zero flag. (I don=E2=80=99t know, it seems useful to me in gen= eral. For example, when you convert to a new block device. The biggest drawback I see is that people might use it blindly and then complain that their image contains garbage...) Max --eW7H4EzN1u3SAEA1rZRP9qMWiy2nplFMm-- --azLSSi2pvb7k4AHmq0szb48ikED4nqMnt Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl4ge1IACgkQ9AfbAGHV z0Bp2ggAp+Z7ms1a7qag3cxwqOEDEN5slE43yretasjuGBrVfyPKq8w82pQOzBLK mkNcxx7jc40LsVGZnQI42atkfWz4cydQ1s4ZMZpxcTT6hoU7eodfqykggWdgYgv2 gtrgUZaR5whuoF+sd5Hs2+DA6raZsftNxL9O5qibTtqd+HmZ4ksaa8+q15F8szMN vehtP011xxMBFIDi4wQf/eumhaK6ZoBBh1g1ndCdXCjYmmdQjRpwwoplQFYbU63I 0mfDmxXl7AkXHkiiSTHRu4vzB3oeNqajeEsigC8qs4pqxTZeuTRvCPrkNe4pXN37 i5A1lzNvXc+wTcDlGFYAMWz7FYJX1w== =6gZg -----END PGP SIGNATURE----- --azLSSi2pvb7k4AHmq0szb48ikED4nqMnt--