From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43697) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eEJ9l-0003JO-AA for qemu-devel@nongnu.org; Mon, 13 Nov 2017 13:08:26 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eEJ9k-0003Cw-7L for qemu-devel@nongnu.org; Mon, 13 Nov 2017 13:08:25 -0500 References: <94700229-5afe-159f-9453-f507b9c83085@redhat.com> From: Eric Blake Message-ID: <0c42f84d-9096-3f7b-c71d-664a119bc8a2@redhat.com> Date: Mon, 13 Nov 2017 12:08:16 -0600 MIME-Version: 1.0 In-Reply-To: <94700229-5afe-159f-9453-f507b9c83085@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="btMBvQuKo1QUkX4tOlaAqFxOokkjEhc78" 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: Peter Maydell , QEMU Developers Cc: Kevin Wolf , Qemu-block , Max Reitz This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --btMBvQuKo1QUkX4tOlaAqFxOokkjEhc78 From: Eric Blake To: Peter Maydell , QEMU Developers Cc: Kevin Wolf , Qemu-block , Max Reitz Message-ID: <0c42f84d-9096-3f7b-c71d-664a119bc8a2@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> In-Reply-To: <94700229-5afe-159f-9453-f507b9c83085@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 11/13/2017 11:58 AM, Eric Blake wrote: >>> qemu-system-aarch64: -drive if=3Dnone,file=3Dhda.qcow2,format=3Dqcow,= id=3Dhd: >>> Unsupported qcow version 3 >> >> ah, this means it wants "format=3Dqcow2". >=20 > Oh, I should have read this followup before writing my other reply. >=20 >> >> 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. >=20 > 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. And having the qcow2 driverautomatically be able to open a qcow v1 image 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. Another observation: is there any official documentation for the qcow (v1) format? I know it's an outdated format that we no longer recommend for new image creation, but it's sad when I have to resort to a google search to find old posts like this: https://people.gnome.org/~markmc/qcow-image-format-version-1.html rather than being able to see the documentation of v1 alongside v2 in the qemu.git repository. At any rate, since qcow and qcow2 share the same 4-byte magic number and version field, it explains why both drivers are able to identify (but fail to open) the files of the other version number. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org --btMBvQuKo1QUkX4tOlaAqFxOokkjEhc78 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAloJ35AACgkQp6FrSiUn Q2qsHAf6ApamRjiqu5ehJG8g2lvf81ORFK78w61KTIZTzJ1odppxI7DhZ2LWpanb euIr71CrxzgdHD8O2w+AQGXA8ZdU23E8CxzlUAyoHDF1XAgRRY+VPZP97TZtBIEf kncmCUhB2LESvGRpvH6LNysjeOq5TsoISQomAxA3tlfto33hCOc2pxyexLcBWWbG diUVR17vAWgVPck4ia/lKfmHVZEhfkAtDKNQ2v6hGgSDCLrKXFaSBg9Hx2zcnt+f OXVTe4P0uq0Ct2EWvweBb19iTffPeGgNtLYI1omEFj9QfVivqHM7bod3nE/fiHVn lKvytt+yUXnsKtadzKeYxv7I0xp1Bg== =mreZ -----END PGP SIGNATURE----- --btMBvQuKo1QUkX4tOlaAqFxOokkjEhc78--