From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:53951) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h1VtX-0000F1-Hy for qemu-devel@nongnu.org; Wed, 06 Mar 2019 07:43:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h1VtW-0006qH-Mu for qemu-devel@nongnu.org; Wed, 06 Mar 2019 07:43:35 -0500 References: <20190227172256.30368-1-kwolf@redhat.com> <20190227172256.30368-4-kwolf@redhat.com> <20190301161724.GB18260@stefanha-x1.localdomain> <20190306095147.GF22159@stefanha-x1.localdomain> From: Eric Blake Message-ID: Date: Wed, 6 Mar 2019 06:43:30 -0600 MIME-Version: 1.0 In-Reply-To: <20190306095147.GF22159@stefanha-x1.localdomain> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="IKjfvwoBb0kI23egAhJlHv8NFIq9JvHyx" Subject: Re: [Qemu-devel] [Qemu-block] [PATCH 03/20] qcow2: Extend spec for external data files List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --IKjfvwoBb0kI23egAhJlHv8NFIq9JvHyx From: Eric Blake To: Stefan Hajnoczi Cc: Kevin Wolf , qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com Message-ID: Subject: Re: [Qemu-devel] [Qemu-block] [PATCH 03/20] qcow2: Extend spec for external data files References: <20190227172256.30368-1-kwolf@redhat.com> <20190227172256.30368-4-kwolf@redhat.com> <20190301161724.GB18260@stefanha-x1.localdomain> <20190306095147.GF22159@stefanha-x1.localdomain> In-Reply-To: <20190306095147.GF22159@stefanha-x1.localdomain> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable On 3/6/19 3:51 AM, Stefan Hajnoczi wrote: > On Fri, Mar 01, 2019 at 10:32:27AM -0600, Eric Blake wrote: >> On 3/1/19 10:17 AM, Stefan Hajnoczi wrote: >>> On Wed, Feb 27, 2019 at 06:22:39PM +0100, Kevin Wolf wrote: >>>> @@ -148,6 +170,7 @@ be stored. Each extension has a structure like t= he following: >>>> 0x6803f857 - Feature name table >>>> 0x23852875 - Bitmaps extension >>>> 0x0537be77 - Full disk encryption header po= inter >>>> + 0x44415441 - External data file name >>> >>> This new header extension isn't described in this patch? >> >> I asked the same on v1, and the answer (which remains valid) is that >> neither is 0xe2792aca Backing file format name. (In other words, both= >> extensions are simple enough as a single file name to be implicitly >> described by the reference to the header in the earlier text). Making= >> both explicit wouldn't hurt my feelings, but I don't see it as a >> showstopper to the patch as-is. >=20 > The spec should make the representation clear. Is it a NUL-terminated > string or is the length dictated by the header extension length field? My understanding is length determined by the header field, with optional NUL padding out to the alignment boundary (but that also means that it does NOT necessarily have a trailing NUL on disk if sizing matches alignment). But yes, being explicit never hurts. >=20 > Otherwise implementors are forced to look at the QEMU source code or > guess based on hex dumping example files :(. Indeed, cleaning up the existing Backing file format name is worth doing (at which point this should follow suit). But it still sounds like a separate patch, at which point it becomes a question of ordering - if the cleanup lands first, then this needs to rebase to do the same; if this lands first, then the cleanup does both headers at once. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org --IKjfvwoBb0kI23egAhJlHv8NFIq9JvHyx Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAlx/wHIACgkQp6FrSiUn Q2peNQf/eQIFfT469W/CklfWMmGtf0+7y2+pUR+YvcDoUuyG1DdEhglUZf/qpm9e YY2qmlj9QF3gMHOmfGvs/sQPNr2qfsl+IzvlmoJ5D9dINRNizMu2V6EzNs3XZaGW Kkx0RYD9AWeaOlIRdMCRu3sx8TjjbPXPC+QsIQpcLBwI3tz8GEPCx3dlgz04x9Ww vu9puY9MIycLyAAbdhWqX/73TJlnaD4eQvjW0wN6PGZSSY3eARedD0dAh/5+Achw bunPoDvx5f3uT8uM++T6zbcQSFLVEhsinEoul83WoVkPoEOwqfzSjm2v9Ha2zF49 D18BvLK7/lZ2KBWzncZzJXN+zE5LPA== =4RU6 -----END PGP SIGNATURE----- --IKjfvwoBb0kI23egAhJlHv8NFIq9JvHyx--