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Thu, 2 Jul 2020 09:57:47 +0000 (UTC) Subject: Re: [PATCH v9 14/34] qcow2: Add QCow2SubclusterType and qcow2_get_subcluster_type() To: Alberto Garcia , qemu-devel@nongnu.org References: <6ee75696d3eaed56b46e91fe242fdfab51feb066.1593342067.git.berto@igalia.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: <6c06d36e-c074-fff0-fad8-fa96962b4906@redhat.com> Date: Thu, 2 Jul 2020 11:57:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="3wi3PFeZ5yvi0QCn9ANfGGkLme5v4eGs4" Received-SPF: pass client-ip=205.139.110.120; envelope-from=mreitz@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/02 04:00:43 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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 , Derek Su , Vladimir Sementsov-Ogievskiy , 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) --3wi3PFeZ5yvi0QCn9ANfGGkLme5v4eGs4 Content-Type: multipart/mixed; boundary="mcSag7eap2wCbJ8CbnZbXyuQg8vCpJ4L8" --mcSag7eap2wCbJ8CbnZbXyuQg8vCpJ4L8 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 01.07.20 18:26, Alberto Garcia wrote: > On Wed 01 Jul 2020 02:52:14 PM CEST, Max Reitz wrote: >>> if (l2_entry & QCOW_OFLAG_COMPRESSED) { >>> return QCOW2_CLUSTER_COMPRESSED; >>> - } else if (l2_entry & QCOW_OFLAG_ZERO) { >>> + } else if ((l2_entry & QCOW_OFLAG_ZERO) && !has_subclusters(s)) { >> >> OK, so now qcow2_get_cluster_type() reports zero clusters to be normal >> or unallocated clusters when there are subclusters. Seems weird to >> me, because zero clusters are invalid clusters then. >=20 > I'm actually hesitant about this. >=20 > In extended L2 entries QCOW_OFLAG_ZERO does not have any meaning so > technically it doesn't need to be checked any more than the other > reserved bits (1 to 8). Good point. That convinces me. > The reason why we would want to check it is, of course, because that bit > does have a meaning in regular L2 entries. >=20 > But that bit is ignored in images with subclusters so the only reason > why we would check it is to report corruption, not because we need to > know its value. Sure. But isn=E2=80=99t that the whole point of having QCOW2_SUBCLUSTER_IN= VALID in the first place? > It's true that we do check it in v2 images, although in that case the > entries are otherwise identical and there is a way to convert between > both types. >=20 >> I preferred just reporting them as zero clusters and letting the >> caller deal with it, because it does mean an error in the image and so >> it should be reported. >=20 > Another alternative would be to add QCOW2_CLUSTER_INVALID and we could > even include there other cases like unaligned offsets and things like > that. But that would also affect the code that repairs corrupted images. Interesting. Well, and that=E2=80=99d be definitely too much for this seri= es, as you already said. So: Reviewed-by: Max Reitz --mcSag7eap2wCbJ8CbnZbXyuQg8vCpJ4L8-- --3wi3PFeZ5yvi0QCn9ANfGGkLme5v4eGs4 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl79r5oACgkQ9AfbAGHV z0CGJAf/Uy0zCamRYcFu5WQGEGgXd5zNo1J3g5YZ2oQ7oVPdzJuTBoC5z3+PIX4r TLZ7X+4M5jYQZt1FxQqo9311cwZhC8zKcXW4XTawwtcurirr7/fb39VlLKumvHJJ oWb7O3JvJmquwlqDj8B0nJoKNYGyxw44Zlr7dUcvJF3K0RhTyAOaELD5eR2+quj6 NYe77RPQ5TduO/Ij4gS5p7Z30Y2RmwFzucyCeS6+Lvc8nD8+0Z35N1i6WuoUssq9 P1ivcnCQ7YE9KdhjOgModdF8KJMruqSyMhF9nfzZHoF9Ofdcdta6KjpBWzPj1ohF m4eEpAuviJZhTrbd4bsB5rGPsS36sQ== =B3EN -----END PGP SIGNATURE----- --3wi3PFeZ5yvi0QCn9ANfGGkLme5v4eGs4--