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 B086BC04EB5 for ; Fri, 7 Feb 2020 15:06:27 +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 7C1A6214AF for ; Fri, 7 Feb 2020 15:06:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UB6g6YUS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7C1A6214AF 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]:58914 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j05D8-0000fP-Kq for qemu-devel@archiver.kernel.org; Fri, 07 Feb 2020 10:06:26 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33450) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j05AZ-0004XR-RC for qemu-devel@nongnu.org; Fri, 07 Feb 2020 10:03:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j05AY-0000iu-AX for qemu-devel@nongnu.org; Fri, 07 Feb 2020 10:03:47 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:53254 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 1j05AY-0000gO-4U for qemu-devel@nongnu.org; Fri, 07 Feb 2020 10:03:46 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581087825; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=xQR15/3try4pw2bjapwOtPcO2QuHAmUU7LxpVN9mHxw=; b=UB6g6YUS2DW50s1CzuebndAlGjNxB161X1ENsAvA7fVu8kGttVNH8PKu3n+QFoNA8OivwU LNsfrxNmlmyjXPpxwJ0Au9J7g7efjxC+8UN5vYIgVG+JaE7sss4DwaWTuQ9krzVUMSYGXp QCsUY3TsITFBUomT5+Vw1zcgdIgzxlk= 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-93-BgyegY_ENlyDTzWyZ4NlYg-1; Fri, 07 Feb 2020 10:03:37 -0500 X-MC-Unique: BgyegY_ENlyDTzWyZ4NlYg-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id EC291101FC64; Fri, 7 Feb 2020 15:03:35 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-14.ams2.redhat.com [10.36.117.14]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8A87D85785; Fri, 7 Feb 2020 15:03:32 +0000 (UTC) Subject: Re: [PATCH v3 1/1] qemu-img: Add --target-is-zero to convert To: Vladimir Sementsov-Ogievskiy , Eric Blake , David Edmondson , qemu-devel@nongnu.org References: <20200204095246.1974117-1-david.edmondson@oracle.com> <20200204095246.1974117-2-david.edmondson@oracle.com> <90f3f74b-6154-d7ce-4e0e-ba4422f7da11@redhat.com> <91c3d45b-4c27-d366-6dd9-5c27164cce35@virtuozzo.com> <92ca6082-a3a6-c116-d1cc-e9810280c0c6@redhat.com> <38ac63ec-af49-d9d5-c1d4-e45614b71d4c@redhat.com> <570489b5-8d1b-27c4-01d3-0e63130d2c57@redhat.com> <99dc03a7-f93a-bdee-f38d-ac5aae8a3ca9@virtuozzo.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: <33849f7f-1ae9-126c-28b8-f9a5602aa2d0@redhat.com> Date: Fri, 7 Feb 2020 16:03:31 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <99dc03a7-f93a-bdee-f38d-ac5aae8a3ca9@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="CMIWMNJFZkvkGw94eoIqbDttsvHMe9w0O" 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: , Cc: qemu-block@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) --CMIWMNJFZkvkGw94eoIqbDttsvHMe9w0O Content-Type: multipart/mixed; boundary="TvV061wtlUWtzgYldk3Uc03PF8vjuLBWk" --TvV061wtlUWtzgYldk3Uc03PF8vjuLBWk Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 07.02.20 15:53, Vladimir Sementsov-Ogievskiy wrote: > 07.02.2020 17:41, Max Reitz wrote: >> On 07.02.20 13:07, Vladimir Sementsov-Ogievskiy wrote: >>> 07.02.2020 13:33, Max Reitz wrote: >>>> On 04.02.20 15:23, Eric Blake wrote: >>>>> On 2/4/20 7:59 AM, Vladimir Sementsov-Ogievskiy wrote: >>>>> >>>>>>> I understand that it is safer to have restrictions now and lift the= m >>>>>>> later, than to allow use of the option at any time and leave room >>>>>>> for >>>>>>> the user to shoot themselves in the foot with no way to add safety >>>>>>> later.=C2=A0 The argument against no backing file is somewhat >>>>>>> understandable (technically, as long as the backing file also reads >>>>>>> as all zeroes, then the overall image reads as all zeroes - but why >>>>>>> have a backing file that has no content?); the argument requiring -= n >>>>>>> is a bit weaker (if I'm creating an image, I _know_ it reads as all >>>>>>> zeroes, so the --target-is-zero argument is redundant, but it >>>>>>> shouldn't hurt to allow it). >>>>>> >>>>>> I know that it reads as all zeroes, only if this format provides zer= o >>>>>> initialization.. >>>>>> >>>>>>> >>>>>>>> +++ b/qemu-img.c >>>>>>> >>>>>>>> @@ -2247,6 +2256,11 @@ static int img_convert(int argc, char >>>>>>>> **argv) >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= warn_report("This will become an error in future QEMU >>>>>>>> versions."); >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>>>>>>> +=C2=A0=C2=A0=C2=A0 if (s.has_zero_init && !skip_create) { >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 error_report("--target= -is-zero requires use of -n flag"); >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto fail_getopt; >>>>>>>> +=C2=A0=C2=A0=C2=A0 } >>>>>>> >>>>>>> So I think we could drop this hunk with no change in behavior. >>>>>> >>>>>> I think, no we can't. If we allow target-is-zero, with -n, we'd >>>>>> better >>>>>> to check that what we are creating is zero-initialized (format has >>>>>> zero-init), and if not we should report error. >>>>>> >>>>> >>>>> Good call.=C2=A0 Yes, if we allow --target-is-zero without -n, we MUS= T >>>>> insist >>>>> that bdrv_has_zero_init() returns 1 (or, after my followup series, >>>>> bdrv_known_zeroes() includes BDRV_ZERO_CREATE). >>>> >>>> Why? >>>> >>>> I could imagine a user creating a qcow2 image on some block device wit= h >>>> preallocation where we cannot verify that the result will be zero.=C2= =A0 But >>>> they want qemu not to zero the device, so they would specify >>>> --target-is-zero. >>> >>> If user create image, setting --target-is-zero is always valid. But if >>> we in >>> same operation create the image automatically, having --target-is-zero, >>> when >>> we know that what we are creating is not zero is misleading and should >>> fail.. >> >> bdrv_has_zero_init() doesn=E2=80=99t return false only for images that w= e know >> are not zero.=C2=A0 It returns true for images where we know they are.= =C2=A0 But >> if we don=E2=80=99t know, then it returns false also. >=20 > yes, but we don't have better check. Correct, but maybe the user knows more, hence why it may make sense for them to provide us with some information we don=E2=80=99t have. >>> If we want to add a behavior to skip zeros unconditionally, we should >>> call new >>> option --skip-zeroes, to clearly specify what we want. >> >> It was my impression that this was exactly what --target-is-zero means >> and implies. >> >=20 > For me it sounds strange that user has better knowledge about what Qemu > creates than Qemu itself. And if it so - it should be fixed in Qemu, > rather than creating user interface to hint Qemu what it does. I brought an example where qemu cannot know whether the image is zero (preallocation on a block device), but the user / management layer might know. Max --TvV061wtlUWtzgYldk3Uc03PF8vjuLBWk-- --CMIWMNJFZkvkGw94eoIqbDttsvHMe9w0O Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl49fEMACgkQ9AfbAGHV z0D3EAf/XYsDKkM0RtFpjkjxD4bkhoBL7bP0cZhLsUtkqgsrGQgGta+rjly23Q3O tL9gBpjocyGgeEAMahoqtWt0G7zGRofbmenHB0WoaWuKQ8NEMF7vTAnN43GaJOMK SA8GTnsp5OJaIxXznwH6bK79PizqYYQ2em2CnqInRyAq2qALRPPn++zdMBQNPm9s TZPmSzbSL7awWc+GrN5MnSfgu5/boXJvJiSCJQyjASF3XnjikT6H3VOMwFJun8PK S08YKd/s3xJmPiY4EAiEtvdCsmlXj+N97dTz1yc4v718+9sTgsgExgut4ZOJYaeN EXoFaqCIvdIGjAQwFrrIk/oDOYBD4w== =V3gR -----END PGP SIGNATURE----- --CMIWMNJFZkvkGw94eoIqbDttsvHMe9w0O--