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=-2.5 required=3.0 tests=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 F2C95C49ED6 for ; Wed, 11 Sep 2019 11:03:44 +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 C72842089F for ; Wed, 11 Sep 2019 11:03:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C72842089F 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]:49500 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i80PX-0000qx-SZ for qemu-devel@archiver.kernel.org; Wed, 11 Sep 2019 07:03:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59370) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i80Mp-0007pR-UJ for qemu-devel@nongnu.org; Wed, 11 Sep 2019 07:00:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i80Mo-0003t4-DI for qemu-devel@nongnu.org; Wed, 11 Sep 2019 07:00:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33574) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i80Mj-0003rM-Gw; Wed, 11 Sep 2019 07:00:49 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 540FD30860CA; Wed, 11 Sep 2019 11:00:48 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-116-94.ams2.redhat.com [10.36.116.94]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AC5571001959; Wed, 11 Sep 2019 11:00:46 +0000 (UTC) To: Kevin Wolf References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-23-mreitz@redhat.com> <20190910145229.GI4446@localhost.localdomain> <20190911065517.GA4907@localhost.localdomain> <20190911082743.GC4907@localhost.localdomain> <20190911103123.GE4907@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: Date: Wed, 11 Sep 2019 13:00:44 +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: <20190911103123.GE4907@localhost.localdomain> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="9uxkJB5cBs6V9ZLlEHHDbEHt08buEWqNa" X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Wed, 11 Sep 2019 11:00:48 +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 v6 22/42] block: Fix bdrv_get_allocated_file_size's fallback 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: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org, 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) --9uxkJB5cBs6V9ZLlEHHDbEHt08buEWqNa Content-Type: multipart/mixed; boundary="mARJXUyEctLFAkeEsWNtDP2kRqVaxRAey"; protected-headers="v1" From: Max Reitz To: Kevin Wolf Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Vladimir Sementsov-Ogievskiy Message-ID: Subject: Re: [PATCH v6 22/42] block: Fix bdrv_get_allocated_file_size's fallback References: <20190809161407.11920-1-mreitz@redhat.com> <20190809161407.11920-23-mreitz@redhat.com> <20190910145229.GI4446@localhost.localdomain> <20190911065517.GA4907@localhost.localdomain> <20190911082743.GC4907@localhost.localdomain> <20190911103123.GE4907@localhost.localdomain> In-Reply-To: <20190911103123.GE4907@localhost.localdomain> --mARJXUyEctLFAkeEsWNtDP2kRqVaxRAey Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 11.09.19 12:31, Kevin Wolf wrote: > Am 11.09.2019 um 12:00 hat Max Reitz geschrieben: >> On 11.09.19 10:27, Kevin Wolf wrote: >>> Am 11.09.2019 um 09:37 hat Max Reitz geschrieben: >>>> On 11.09.19 08:55, Kevin Wolf wrote: >>>>> Well, by default the primary child, which should cover like 90% of = the >>>>> drivers? >>>> >>>> Hm, yes. >>>> >>>> But I still think that the drivers that do not want to count every >>>> single non-COW child are the exception. >>> >>> They are, but drivers that want to count more than their primary node= >>> are exceptions, too. And I think you're more likely to remember addin= g >>> the callback when you want to have a certain feature, not when you do= n't >>> want to have it. >>> >>> I really think we're likely to forget adding the callback where we ne= ed >>> to disable the feature. >> >> Well, I mean, we did forget adding it for qcow2. >=20 > I'm afraid I have to agree. So the conclusion is that we won't get it > right anyway? >=20 >>> I can see two options that should address both of our views: >>> >>> 1. Just don't have a fallback at all, make the callback mandatory and= >>> provide implementations in block.c that can be referred to in >>> BlockDriver. Not specifying the callback causes an assertion failu= re, >>> so we'd hopefully notice it quite early (assuming that we run eith= er >>> 'qemu-img info' or 'query-block' on a configuration with the block= >>> driver, but I think that's faily safe to assume). >> >> Hm. Seems a bit much, but if we can=E2=80=99t agree on what=E2=80=99s= a good general >> implementation that works for everything, this is probably the only >> thing that would actually keep us from forgetting to add special cases= =2E >> >> Though I actually don=E2=80=99t know. I=E2=80=99d probably add two gl= obally available >> helpers, one that returns the sum of everything but the backing node, >> and one that just returns the primary node. >=20 > Yes, I think this is the same as I meant by "provide implementations in= > block.c". >=20 >> Now if I were to make qcow2 use the primary node helper function, woul= d >> we have remembered changing it once we added a data file? >> >> Hmm. Maybe not, but it should be OK to just make everything use the s= um >> helper, except the drivers that want the primary node. That should wo= rk >> for all cases. (I think that whenever a format driver suddenly gains >> more child nodes, we probably will want to count them. OTOH, everythi= ng >> that has nodes that shouldn=E2=80=99t be counted probably always wants= to use >> the primary node helper function from the start.) >=20 > The job filter nodes have only one child currently, which should be > counted. We'll add other children that shouldn't be counted only later.= >=20 > But we already have an idea of what possible extensions look like, so w= e > can probably choose the right function from the start. Yep. >>> 2. Make the 90% solution a 100% solution: Allow drivers to have multi= ple >>> storage children (for vmdk) and then have the fallback add up the >>> primary child plus all storage children. This is what I suggested = as >>> the documented semantics in my initial reply to this patch (that y= ou >>> chose not to answer). >> >> I didn=E2=80=99t answer that because I didn=E2=80=99t disagree. >> >>> Adding the size of storage children covers qcow2 and vmdk. >> >> That=E2=80=99s of course exactly what we=E2=80=99re trying to do, but = the question is, >> how do we figure out that storage children? Make it a per-BdrvChild >> attribute? That seems rather heavy-handed, because I think we=E2=80=99= d need it >> only here. >=20 > Well, you added bdrv_storage_child().I'd argue this interface is wrong Yes, it probably is. > because it assumes that only one storage child exists. You just didn't > implement it for vmdk so that the problem didn't become apparent. It > would have to return a list rather than a single child. So fixing the > interface and then using it is what I was thinking. >=20 > Now that you mention a per-BdrvChild attribute, however, I start to > wonder if the distinction between COW children, filter children, storag= e > children, metadata children, etc. isn't really what BdrvChildRole was > supposed to represent? That=E2=80=99s a good point. > Maybe we want to split off child_storage from child_file, though it's > not strictly necessary for this specific case because we want to treat > both metadata and storage nodes the same. But it could be useful for > other users of bdrv_storage_child(), if there are any. Possible. Maybe it turns out that at least for this series I don=E2=80=99= t need bdrv_storage_child() at all. >>> As the job filter won't declare the target or any other involved >>> nodes their storage nodes (I hope), this will do the right thing f= or >>> them, too. >>> >>> For quorum and blkverify both ways could be justifiable. I think t= hey >>> probably shouldn't declare their children as storage nodes. They a= re >>> more like filters that don't have a single filtered node. So some >>> kind of almost-filters. >> >> I don=E2=80=99t think quorum is a filter, and blkverify can only be ju= stified to >> be a filter because it quits qemu when there is a mismatch. >> >> The better example is replication, but that has a clear filtered child= >> (the primary node). >> >> >> So all in all I think it=E2=80=99s best to make the callback mandatory= and add >> two global helper functions. That=E2=80=99s simple enough and should = prevent >> us from making mistakes by forgetting to adjust something in the >> future. >=20 > Yes, that should work. >=20 > We should probably still figure out what the relationship between the > child access functions and child roles is, even if we don't need it for= > this solution. But it feels like an important part of the design. Hm. It feels like something that should be done before this series, actually. So I think we should add at least a child role per child access function so that they match? And then maybe in bdrv_attach_child() assert that a BDS never has more than one primary or filtered child (a filtered child acts as a primary child, too), or more than one COW child. (And that these are always in bs->file or bs->backing so the child access functions do work.) Max --mARJXUyEctLFAkeEsWNtDP2kRqVaxRAey-- --9uxkJB5cBs6V9ZLlEHHDbEHt08buEWqNa Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl1409wACgkQ9AfbAGHV z0DAnAgAg66yrj4fD+acyRShTpNUjdo0t64JUKYwrEtlUFC6+HeKWn7KGoHSBwYd bbHxCH0DAz+dPMOkDhXmKiZYL4d9wQOHBkpSvpabLXyKq9hEN91W68TH2jw38iQt 9fk/sBJoIOWnzcmesGpOJaitQUlfSl4mcLdX6mrXosytdFMVSYNBBVxypwgsogn5 LZQXmeLzBj97d29jsNtcIqLa5ZMi8NdGF51LfqzSADf3DuklyZUnZkRqqwNwVd7X 2gef02oWGH2EZ8r30d2qKhKo4Ax5+8Y7qR8YMvq+sQU5f47/riDh9SB1TWHtx7fv avvsBmzZ5grqs6Rro92hnQWfbsrpcQ== =2gHV -----END PGP SIGNATURE----- --9uxkJB5cBs6V9ZLlEHHDbEHt08buEWqNa--