From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36627) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dUZiS-0000J6-NI for qemu-devel@nongnu.org; Mon, 10 Jul 2017 10:31:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dUZiR-00075k-Ml for qemu-devel@nongnu.org; Mon, 10 Jul 2017 10:31:12 -0400 References: <1498733831-15254-1-git-send-email-pl@kamp.de> <1498733831-15254-2-git-send-email-pl@kamp.de> <20170710125857.GD5772@noname.redhat.com> <11427303-a0cd-ee7b-edb4-1cdf9b90c0af@kamp.de> <20170710135021.GJ5772@noname.redhat.com> From: Eric Blake Message-ID: Date: Mon, 10 Jul 2017 09:31:02 -0500 MIME-Version: 1.0 In-Reply-To: <20170710135021.GJ5772@noname.redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="3MT77N7fMUFW8CKWU7OmwRpCNkiLCa4Uf" Subject: Re: [Qemu-devel] [PATCH V2 1/8] docs: add compress format extension to qcow2 spec List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf , Peter Lieven Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, lersek@redhat.com, den@openvz.org, mreitz@redhat.com, berrange@redhat.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --3MT77N7fMUFW8CKWU7OmwRpCNkiLCa4Uf From: Eric Blake To: Kevin Wolf , Peter Lieven Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, lersek@redhat.com, den@openvz.org, mreitz@redhat.com, berrange@redhat.com Message-ID: Subject: Re: [PATCH V2 1/8] docs: add compress format extension to qcow2 spec References: <1498733831-15254-1-git-send-email-pl@kamp.de> <1498733831-15254-2-git-send-email-pl@kamp.de> <20170710125857.GD5772@noname.redhat.com> <11427303-a0cd-ee7b-edb4-1cdf9b90c0af@kamp.de> <20170710135021.GJ5772@noname.redhat.com> In-Reply-To: <20170710135021.GJ5772@noname.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 07/10/2017 08:50 AM, Kevin Wolf wrote: > We have regretted enough things that were defined a bit sloppily just > for convenience that I'd rather not make this mistake again when we can= > avoid it. Agreed. Another consideration: defining redundant information is trickier to maintain because correct implementations have to check that both points are consistent with one another. >=20 >>>> + 17 - 19: Reserved for future use, must be zero. >>> We don't need this for now because byte 16 will be the final one in t= his >>> struct. >>> >>>> + 20 - 23: extra_data_size >>>> + Size of compress format specific extra data. >>>> + For now, as no format specifies extra data, >>>> + extra_data_size is reserved and should be zero. >>>> + >>>> + variable: extra_data >>>> + Extra data with additional parameters for the co= mpress >>>> + format, occupying extra_data_size bytes. >>> extra_data_size isn't necessary because we already have the length of= >>> the header extension, so we know how long the whole thing is. >>> extra_data isn't necessary because we'll just add new fields at the e= nd >>> if we want to add something. >> >> I was asked to add it altough it is redundant. >=20 > Who asked this, and did they have a good reason for it? May have been me, or may have been implied by my comments, but I agree that the overall extension header covers this, so we don't need a redundant form. So as long as the overall extension header length is good enough, I'm okay avoiding redundancies. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org --3MT77N7fMUFW8CKWU7OmwRpCNkiLCa4Uf Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJZY4+mAAoJEKeha0olJ0NqmmIIAJur4GIASmYIInu8cUGIX7cZ Btdj3lkakTcgGPf2RGrMVlclRu/32KlYWoRjDlQ7R+SiSgii8mMGBpXZwZwHEq9P Ah4hrN9WlSEKyc4Bx7J0Iuz6RoPdyCE3tQ7jB2ZOGKxx7mMt95DB0IJOIbpDdhPR EHvR4vaI8PbYFEobgZxg7suubrCoaalsN4mg4mF9whgStiJbfh5wAABEUcuHY2iL 0yqIA+b2n7TQkI24H8g9aaRDCla5j4wPYUe5x2N226Z7e3phKYk/C3FuMLb9+5WU VCUY0za1YROyazBlZRwyOZjrm99Qt4HT36fRV5kx5VWkZSCt6BtFkLR+ofLBlYs= =LIFh -----END PGP SIGNATURE----- --3MT77N7fMUFW8CKWU7OmwRpCNkiLCa4Uf--