From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56961) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WsNq9-00079n-Uc for qemu-devel@nongnu.org; Wed, 04 Jun 2014 22:55:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WsNq4-0000z8-Vw for qemu-devel@nongnu.org; Wed, 04 Jun 2014 22:55:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59106) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WsNq4-0000z1-MO for qemu-devel@nongnu.org; Wed, 04 Jun 2014 22:55:36 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s552tan0022506 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Wed, 4 Jun 2014 22:55:36 -0400 Message-ID: <538FDC27.3020607@redhat.com> Date: Wed, 04 Jun 2014 20:55:35 -0600 From: Eric Blake MIME-Version: 1.0 References: <538FA3C8.7000108@redhat.com> <20140605001214.GA2639@localhost.localdomain> <538FCDF2.4080409@redhat.com> <20140605020906.GA10963@T430.nay.redhat.com> In-Reply-To: <20140605020906.GA10963@T430.nay.redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Rxf5GNnILhc0HpXM58qpOla1viOpFte2h" Subject: Re: [Qemu-devel] active block commit bug? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: Jeff Cody , akong@redhat.com, "qemu-devel@nongnu.org" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --Rxf5GNnILhc0HpXM58qpOla1viOpFte2h Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 06/04/2014 08:09 PM, Fam Zheng wrote: >> Sounds like we have an off-by-one condition if empty files behave >> differently from other files. We ought to fix that bug (not that your= >> normal guest will ever have a 0-length backing file, but this was what= I >> was trying to use for libvirt's probing of whether active commit is >> supported) >> >=20 > Yes, agreed, this special case is only going to make management confuse= d. I > will send a patch to fix this. Thanks. >=20 > Eric, is this a good way to probe the active commit? I was expecting fu= ll > instrospection of QMP could do it, but I don't know about the status of= that > piece of work. Amos, any ideas? Introspection already missed qemu 2.0 when active commit was added; and we're close enough to soft freeze for 2.1 that I'm guessing it will miss 2.1 as well :( So yes, I'm experimenting with how to learn if active commit works by seeing what error message differences I can trigger with minimum effort; libvirt will cache what it learns so that it only has to ask once per qemu binary/timestamp, then let the user know up front whether active commit will work. Since there are existing qemu versions that have active commit but not introspection, I'm stuck using this harder probe to avoid a false negative for those older qemu. My other option is to just wait for introspection, or even something intermediate like Jeff's patch to make 'top' optional, and just declare qemu 2.0 active commit as not working - but since it is only the special case of a 0-size file (which is fairly unlikely for any real client use, and certainly something I can avoid in the libvirt probing), it feels a bit harsh to reject 2.0 just for this corner-case bug. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --Rxf5GNnILhc0HpXM58qpOla1viOpFte2h 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 Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJTj9wnAAoJEKeha0olJ0Nq8P0IAI3NqSc9462e0BhSEvpIkMAi gPgjLpELNXt2Cl6fZ3EDMWLHC5tL8f6qv1uxX1aIIqDCRiBXVxbH9gZnWKUM6IPR whunzxdtdgiikMxcHfRdz7zk1jU9MdrzsIW9fygkcG8pJ7TM9RalL5Vea0gtkT+3 P8Juyh3mKur7q3Z6sTk+2Eb1mVSNydToQKAVfE0KCqvrwkyZAuVz9FJb5GXHFtfY I7CFB6svADtgG1ahtib0AcikgL2EW9b9YoQmYQGNHzJrHACXENq0zPQWQQO0T2Lw pJTYobph9E63TAEEaSGJQAOwv/g7Fb2wkPRLJgKo6+zNZ3jhwjwLjNlWtv5PzzA= =N9Mi -----END PGP SIGNATURE----- --Rxf5GNnILhc0HpXM58qpOla1viOpFte2h--