From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33564) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eEbK3-0001Fu-Ul for qemu-devel@nongnu.org; Tue, 14 Nov 2017 08:32:16 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eEbK2-0003bi-Qs for qemu-devel@nongnu.org; Tue, 14 Nov 2017 08:32:15 -0500 References: <94700229-5afe-159f-9453-f507b9c83085@redhat.com> <0c42f84d-9096-3f7b-c71d-664a119bc8a2@redhat.com> From: Max Reitz Message-ID: <9ab7ae12-730d-a4d4-287c-64dcd509b680@redhat.com> Date: Tue, 14 Nov 2017 14:32:05 +0100 MIME-Version: 1.0 In-Reply-To: <0c42f84d-9096-3f7b-c71d-664a119bc8a2@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="KffxMskVWqd17H4tIr0eM02i4DwouqgAD" Subject: Re: [Qemu-devel] using "qemu-img convert -O qcow2" to convert qcow v1 to v2 creates a qcow v3 file? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake , Peter Maydell , QEMU Developers Cc: Kevin Wolf , Qemu-block This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --KffxMskVWqd17H4tIr0eM02i4DwouqgAD From: Max Reitz To: Eric Blake , Peter Maydell , QEMU Developers Cc: Kevin Wolf , Qemu-block Message-ID: <9ab7ae12-730d-a4d4-287c-64dcd509b680@redhat.com> Subject: Re: [Qemu-devel] using "qemu-img convert -O qcow2" to convert qcow v1 to v2 creates a qcow v3 file? References: <94700229-5afe-159f-9453-f507b9c83085@redhat.com> <0c42f84d-9096-3f7b-c71d-664a119bc8a2@redhat.com> In-Reply-To: <0c42f84d-9096-3f7b-c71d-664a119bc8a2@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 2017-11-13 19:08, Eric Blake wrote: > On 11/13/2017 11:58 AM, Eric Blake wrote: >=20 >>>> qemu-system-aarch64: -drive if=3Dnone,file=3Dhda.qcow2,format=3Dqcow= ,id=3Dhd: >>>> Unsupported qcow version 3 >>> >>> ah, this means it wants "format=3Dqcow2". >> >> Oh, I should have read this followup before writing my other reply. >> >>> >>> This is pretty confusing, especially the error message, the >>> output of "file", and the fact that "format=3Dqcow" can't just >>> DTRT if it gets a qcow version 3 (2?), since it can clearly >>> identify what it's got. >> >> Indeed, making the qcow driver smart enough to reopen with the qcow2 >> driver (for both v2 and v3 images) might be an interesting ease-of-use= hack. >=20 > And having the qcow2 driverautomatically be able to open a qcow v1 imag= e > read-only might also be nice - although v1 is lacking so many features > that we'd be insane to let a read-write request of the qcow2 driver > downgrade to qcow. Both seem to be hacks to me, though, which needlessly complicate everythi= ng. Just issuing a deprecation warning when creating qcow v1 images and improving the warning when opening qcow2 (v2/v3) images with the qcow driver should be enough. > Another observation: is there any official documentation for the qcow > (v1) format? I know it's an outdated format that we no longer recommen= d > for new image creation, but it's sad when I have to resort to a google > search to find old posts like this: >=20 > https://people.gnome.org/~markmc/qcow-image-format-version-1.html >=20 > rather than being able to see the documentation of v1 alongside v2 in > the qemu.git repository. Well, do you want to document it? I'd rather deprecate it altogether. Max > At any rate, since qcow and qcow2 share the same 4-byte magic number an= d > version field, it explains why both drivers are able to identify (but > fail to open) the files of the other version number. --KffxMskVWqd17H4tIr0eM02i4DwouqgAD Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQFGBAEBCAAwFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAloK8FUSHG1yZWl0ekBy ZWRoYXQuY29tAAoJEPQH2wBh1c9AY+YIAK8M8TnxIx9/bsLj3jPrTmv50CxDWUB2 rnIefVUqk3G3EaP6qxdXYVBMjX24z+EL8EWWTo3u4uAUrt65e0j066pbpPpmK2l0 yeftbEH1+gyMtTDj9msRN38EV4LRxclQwzySMCIMZSFCCEwhD7tvqTh5DXOQGFmx azOQBzk2gF1IPMD809yYlyigYxWy0DFpqetXiz3D+LOevRBTWrqfPSQZgEtW4kiN KwMDH6i1zWzTuLrp4EJ6hUHE3NghPTViDVSnMy066pidXOamcpNqewHpULnGXOKm lA/hQROQU38Q3wZR/x/YiwDSW3RzHHae2z6m2igQQIWh+SwPSSPr7w4= =1MeB -----END PGP SIGNATURE----- --KffxMskVWqd17H4tIr0eM02i4DwouqgAD--