From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:33428) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UV7N9-0002Sv-Vw for qemu-devel@nongnu.org; Wed, 24 Apr 2013 17:37:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UV7N8-0005n8-Oo for qemu-devel@nongnu.org; Wed, 24 Apr 2013 17:37:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59991) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UV7N8-0005ms-Gr for qemu-devel@nongnu.org; Wed, 24 Apr 2013 17:37:02 -0400 Message-ID: <5178507C.3010007@redhat.com> Date: Wed, 24 Apr 2013 15:37:00 -0600 From: Eric Blake MIME-Version: 1.0 References: <87ppxluwzy.fsf@elfo.elfo> <5176B191.50406@redhat.com> In-Reply-To: <5176B191.50406@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="----enig2BLPTXCUHIWQAWETVHVKS" Subject: Re: [Qemu-devel] KVM call minutes for 2013-04-23 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: KVM devel mailing list , qemu-devel qemu-devel , Osier Yang , quintela@redhat.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) ------enig2BLPTXCUHIWQAWETVHVKS Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 04/23/2013 10:06 AM, Eric Blake wrote: >> >> we can change "drive_mirror" to use a new command to see if there >> are the new features. >=20 > drive-mirror changed in 1.4 to add optional buf-size parameter; right > now, libvirt is forced to limit itself to 1.3 interface (no buf-size or= > granularity) because there is no introspection and no query-* command > that witnesses that the feature is present. Idea was that we need to > add a new query-drive-mirror-capabilities (name subject to bikeshedding= ) > command into 1.5 that would let libvirt know that buf-size/granularity > is usable (done right, it would also prevent the situation of buf-size > being a write-only interface where it is set when starting the mirror > but can not be queried later to see what size is in use). >=20 > Unclear whether anyone was signing up to tackle the addition of a query= > command counterpart for drive-mirror in time for 1.5. Further discussion on this topic: Luiz proposed such a command: https://lists.gnu.org/archive/html/qemu-devel/2013-04/msg04937.html in the meantime, Paolo and I discussed on IRC, and realized that: 1. Current libvirt does not expose buf-size or granularity to the end user. Until a future libvirt release actually wants to use these options, we are in no rush to get it into qemu 1.5; it's okay to leave things in the same state they were in for 1.4, and have qemu 1.6 be the first release that coordinates with a new libvirt release actually wanting to use the options. 2. At least with drive-mirror, the "try-and-fail" approach generates a reasonable-enough error message. Having a capability query may allow libvirt to save time and/or give a better quality error message, but this is one case where not knowing whether the parameter exists is not a fatal flaw to the algorithm, since libvirt can still gracefully recover from attempting to use the parameter (only when the user requested a non-default value). Distros that want to prove their value-added quality-of-implementation can easily backport whatever solution goes into qemu 1.6 for nicer detection into the distro stable build, even if the distro is based on 1.5; libvirt will use the nicer detection when available but should have no problems using the try-and-fail approach otherwise. So at this point, I'm comfortable with not trying to add anything into 1.5 dealing with drive-mirror; it feels like too much of a new feature past soft freeze with no known current client, where we would be better off waiting to 1.6 to get the interface right. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org ------enig2BLPTXCUHIWQAWETVHVKS Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.13 (GNU/Linux) Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJReFB8AAoJEKeha0olJ0Nq9qkH+wQBdBPSVVsaEuRoUYUR4fUn NPC6R8sEDDocHZdPw3lBNDB3NmHbtAePUM0cdjV6UpAUqGDgo7KdVEG9RBI/T2kE zW1VtmjT/W7QzDU5a3+LcPv+YJbCimjuJHolC0FQ9b/6RissFAIWfa3P3FaywJ5J 37EFpednDWlpKzUosUsC09LKqLnYYV9Mo4sZNCY+lhtVFKyn5ynEk2WrtFBjR6VQ f6/k4moGDP5SNm2tzYvGNIxUM8P72xzEo1lWCZFgaAo0IbrIORr5yq2G2mpv8jNm 58gM19KqVDtg8RhJsiIVux4MsnxWCueM2XW/MXKO1eYg4aqar0iNpfTTYH6QBDM= =JhTn -----END PGP SIGNATURE----- ------enig2BLPTXCUHIWQAWETVHVKS--