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bh=qTLCsJxcEE55/fFCKv8Kh44P3psul8EZEHtuNjVWP9M=; b=LiYPlimMEKoXMmzGgr0Dyp5asoiEN1FqcJ0QL/9LSinlRQAvXbKhFlpa/NLFQLMYQI3ytZ 6HwyHcCjLZ3hmUpr2gQv9A4JXqKIKXEzz31b0MEZFtmIIpSTLX6TIwN3skkmGdjkMFvhyZ kW3Weu/xLlkTXhJhh8yoMRH+xRVnfpg= 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-217-VGP4QC1HPFW5Iaz6fndDxQ-1; Wed, 07 Oct 2020 10:35:18 -0400 X-MC-Unique: VGP4QC1HPFW5Iaz6fndDxQ-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 E3248107819D; Wed, 7 Oct 2020 14:34:05 +0000 (UTC) Received: from [10.3.113.66] (ovpn-113-66.phx2.redhat.com [10.3.113.66]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0F9CE78831; Wed, 7 Oct 2020 14:34:04 +0000 (UTC) Subject: Re: [PATCH] qcow2: Document and enforce the QCowL2Meta invariants To: Alberto Garcia , qemu-devel@nongnu.org References: <20201007115217.18013-1-berto@igalia.com> From: Eric Blake Autocrypt: addr=eblake@redhat.com; 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Message-ID: <21d332f9-5174-f552-ff07-8109b3673c52@redhat.com> Date: Wed, 7 Oct 2020 09:34:04 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20201007115217.18013-1-berto@igalia.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Mj1x30xMeXrv7dVGbYd2agmeKci3cmLOy" Received-SPF: pass client-ip=216.205.24.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/07 00:54:30 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.742, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action 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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, Max Reitz 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) --Mj1x30xMeXrv7dVGbYd2agmeKci3cmLOy Content-Type: multipart/mixed; boundary="dYPYqcNPdk5WsGUvEoRlifdhAUEYZ8F32"; protected-headers="v1" From: Eric Blake To: Alberto Garcia , qemu-devel@nongnu.org Cc: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, Max Reitz Message-ID: <21d332f9-5174-f552-ff07-8109b3673c52@redhat.com> Subject: Re: [PATCH] qcow2: Document and enforce the QCowL2Meta invariants References: <20201007115217.18013-1-berto@igalia.com> In-Reply-To: <20201007115217.18013-1-berto@igalia.com> --dYPYqcNPdk5WsGUvEoRlifdhAUEYZ8F32 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 10/7/20 6:52 AM, Alberto Garcia wrote: > The QCowL2Meta structure is used to store information about a part of > a write request that touches clusters that need changes in their L2 > entries. This happens with newly-allocated clusters or subclusters. >=20 > This structure has changed a bit since it was first created and its > current documentation is not quite up-to-date. >=20 > A write request can span a region consisting on a combination of s/on/of/ > clusters of different types, and qcow2_alloc_host_offset() can > repeatedly call handle_copied() and handle_alloc() to add more > clusters to the mix as long as they all are contiguous on the image > file. >=20 > Because of this a write request has a list of QCowL2Meta structures, > one for each part of the request that needs changes in the L2 > metadata. >=20 > Each one of them spans nb_clusters and has two copy-on-write regions > located immediately before and after the middle region that that part > of the write request touches. Even when those regions themselves are Grammatically correct, but the doubled 'that' caught me on my first read. Maybe you want: s/that that part of the write request touches/touched by that part of the write request/ > empty their offsets must be correct because they are used to know the > location of the middle region. >=20 > This was not always the case but it is not a problem anymore > because the only two places where QCowL2Meta structures are created > (calculate_l2_meta() and qcow2_co_truncate()) ensure that the > copy-on-write regions are correctly defined, and so do assertions like > the ones in perform_cow(). >=20 > The conditional initialization of the 'written_to' variable is > therefore unnecessary and is removed by this patch. >=20 > Signed-off-by: Alberto Garcia > --- Reviewed-by: Eric Blake --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org --dYPYqcNPdk5WsGUvEoRlifdhAUEYZ8F32-- --Mj1x30xMeXrv7dVGbYd2agmeKci3cmLOy Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAl990dwACgkQp6FrSiUn Q2rzpAgAkr7XUw2/IX6Gyxptats8RkOc/yCUq8jkFnJtoXS3FSmxemNtEBjDqGec gy2JjaTyp6iYg0TpqhuKmZ7xajwup37CvtjX0wduOi2qzSsQjuYpxe/AmjH95fzb 1ijZ/w111+nSuBq3pHALIfs7HcoPsJJ3lDLafSmw59zzANjAz+VEmBh0j857hCna h5neh94BwsKbBbjvApaGKVJy319BQ17lNpeLjK67X2/D7vdExydYRUFPVsmX3ViR xmtctZi2S+sFJMHSUrSIbRgF7WZpOCW/IJ+/18dOFdYy0qiQJNhVw85vSAXWHWnJ tbLJT6L5q2tD2KU3BumUshIHNMsXAQ== =BBey -----END PGP SIGNATURE----- --Mj1x30xMeXrv7dVGbYd2agmeKci3cmLOy--