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Mon, 24 Aug 2020 14:29:48 +0000 (UTC) Subject: Re: [PATCH v7 41/47] block: Leave BDS.backing_file constant To: Kevin Wolf References: <20200625152215.941773-1-mreitz@redhat.com> <20200625152215.941773-42-mreitz@redhat.com> <20200824131412.GA10708@linux.fritz.box> 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: <280f4c43-e4c5-f29e-54be-91374ed80574@redhat.com> Date: Mon, 24 Aug 2020 16:29:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200824131412.GA10708@linux.fritz.box> 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: 0.003 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="xTxzeU5HvFJ9GgM4mPPQVjSQZ9SU9G3Hj" 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 = 2020/08/24 06:40:32 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -52 X-Spam_score: -5.3 X-Spam_bar: ----- X-Spam_report: (-5.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.956, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-2.25, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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: 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) --xTxzeU5HvFJ9GgM4mPPQVjSQZ9SU9G3Hj Content-Type: multipart/mixed; boundary="7kp97mCrU9SO8HbchdEWAvbSAGtq2W59Q" --7kp97mCrU9SO8HbchdEWAvbSAGtq2W59Q Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 24.08.20 15:14, Kevin Wolf wrote: > Am 25.06.2020 um 17:22 hat Max Reitz geschrieben: >> Parts of the block layer treat BDS.backing_file as if it were whatever >> the image header says (i.e., if it is a relative path, it is relative to >> the overlay), other parts treat it like a cache for >> bs->backing->bs->filename (relative paths are relative to the CWD). >> Considering bs->backing->bs->filename exists, let us make it mean the >> former. >> >> Among other things, this now allows the user to specify a base when >> using qemu-img to commit an image file in a directory that is not the >> CWD (assuming, everything uses relative filenames). >> >> Before this patch: >> >> $ ./qemu-img create -f qcow2 foo/bot.qcow2 1M >> $ ./qemu-img create -f qcow2 -b bot.qcow2 foo/mid.qcow2 >> $ ./qemu-img create -f qcow2 -b mid.qcow2 foo/top.qcow2 >> $ ./qemu-img commit -b mid.qcow2 foo/top.qcow2 >> qemu-img: Did not find 'mid.qcow2' in the backing chain of 'foo/top.qcow= 2' >> $ ./qemu-img commit -b foo/mid.qcow2 foo/top.qcow2 >> qemu-img: Did not find 'foo/mid.qcow2' in the backing chain of 'foo/top.= qcow2' >> $ ./qemu-img commit -b $PWD/foo/mid.qcow2 foo/top.qcow2 >> qemu-img: Did not find '[...]/foo/mid.qcow2' in the backing chain of 'fo= o/top.qcow2' >> >> After this patch: >> >> $ ./qemu-img commit -b mid.qcow2 foo/top.qcow2 >> Image committed. >> $ ./qemu-img commit -b foo/mid.qcow2 foo/top.qcow2 >> qemu-img: Did not find 'foo/mid.qcow2' in the backing chain of 'foo/top.= qcow2' >> $ ./qemu-img commit -b $PWD/foo/mid.qcow2 foo/top.qcow2 >> Image committed. >> >> With this change, bdrv_find_backing_image() must look at whether the >> user has overridden a BDS's backing file. If so, it can no longer use >> bs->backing_file, but must instead compare the given filename against >> the backing node's filename directly. >> >> Note that this changes the QAPI output for a node's backing_file. We >> had very inconsistent output there (sometimes what the image header >> said, sometimes the actual filename of the backing image). This >> inconsistent output was effectively useless, so we have to decide one >> way or the other. Considering that bs->backing_file usually at runtime >> contained the path to the image relative to qemu's CWD (or absolute), >> this patch changes QAPI's backing_file to always report the >> bs->backing->bs->filename from now on. If you want to receive the image >> header information, you have to refer to full-backing-filename. >> >> This necessitates a change to iotest 228. The interesting information >> it really wanted is the image header, and it can get that now, but it >> has to use full-backing-filename instead of backing_file. Because of >> this patch's changes to bs->backing_file's behavior, we also need some >> reference output changes. >> >> Along with the changes to bs->backing_file, stop updating >> BDS.backing_format in bdrv_backing_attach() as well. In order not to >> change our externally visible behavior (incompatibly), we have to let >> bdrv_query_image_info() try to get the image format from bs->backing if >> bs->backing_format is unset. (The QAPI schema describes >> backing-filename-format as "the format of the backing file", so it is >> not necessarily what the image header says, but just the format of the >> file referenced by backing-filename (if known).) >=20 > Why is it okay to change backing-filename incompatibly, but not > backing-filename-format? I hope you=E2=80=99re asking the reverse, i.e. why I don=E2=80=99t change backing-filename-format, too. The answer to that is yeah, why not. :) > I would find it much more consistent if > ImageInfo reported the value from the header in both fields, and > BlockDeviceInfo reported the values actually in use. >=20 > The QAPI schema described ImageInfo as "Information about a QEMU image > file" and runtime state really isn't information about an image file. >=20 > If you want to know the probed image format, you can still look at > backing-image.format. I don't think this change is much different from > what you described above for BlockDeviceInfo.backing_file. Well, OK then. Max --7kp97mCrU9SO8HbchdEWAvbSAGtq2W59Q-- --xTxzeU5HvFJ9GgM4mPPQVjSQZ9SU9G3Hj Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl9DztoACgkQ9AfbAGHV z0B2mQgAgbE7JFb+AsLcOGo6ErokdyKOurWpT9HphancJ+I/5UerImw90B64FtmA NR3Ujf6SP9wSy8+HR2NXTbMKzHe7g5MO0RBAwdGxRqYL2T00h8CSHCfntrneNnEl AW5/NEw9dInDp5+yx0nzDHRKV9V6NgcQyQkNEb6VVuYoblG8a4DUkrTuYW0TMa9y vNqcYOEBP14DRU/mZJeaFVnzn8cIkyX7S6KtXUD8Sx3JJU2Dlnymog5J+aEryPIs aeWNU18/rfFXEZZ4ANa7yVYAgTHJsXtavvbu72VArWoKgtpi8TcNisFvkLJuyvpZ 4hUZVFrnBpd9H3ZmVs8dEyq/j5MAqw== =MAj5 -----END PGP SIGNATURE----- --xTxzeU5HvFJ9GgM4mPPQVjSQZ9SU9G3Hj--