From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:32776) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RzXLz-0004a3-Q7 for qemu-devel@nongnu.org; Mon, 20 Feb 2012 12:48:51 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RzXLv-00034f-In for qemu-devel@nongnu.org; Mon, 20 Feb 2012 12:48:47 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34945) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RzXLv-00034T-44 for qemu-devel@nongnu.org; Mon, 20 Feb 2012 12:48:43 -0500 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q1KHmfWf013511 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Mon, 20 Feb 2012 12:48:42 -0500 Message-ID: <4F428778.8040409@redhat.com> Date: Mon, 20 Feb 2012 10:48:40 -0700 From: Eric Blake MIME-Version: 1.0 References: <58b44a8409ab790a76212958928fa6f3ccbf9096.1329758006.git.jcody@redhat.com> In-Reply-To: <58b44a8409ab790a76212958928fa6f3ccbf9096.1329758006.git.jcody@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------enigC3BAAB10A6195EF785D41D30" Subject: Re: [Qemu-devel] [PATCH 3/3] qapi: Introduce blockdev-query-group-snapshot-failure List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jeff Cody Cc: Kevin Wolf , Luiz Capitulino , qemu-devel@nongnu.org, Markus Armbruster This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigC3BAAB10A6195EF785D41D30 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 02/20/2012 10:31 AM, Jeff Cody wrote: > In the case of a failure in a group snapshot, it is possible for > multiple file image failures to occur - for instance, failure of > an original snapshot, and then failure of one or more of the > attempted reopens of the original. >=20 > Knowing all of the file images which failed could be useful or > critical information, so this command returns a list of strings > containing the filenames of all failures from the last > invocation of blockdev-group-snapshot-sync. Meta-question: Suppose that the guest is running when we issue blockdev-group-snapshot-sync - in that case, qemu is responsible for pausing and then resuming the guest. On success, this makes sense. But what happens on failure? If we only fail at creating one snapshot, but successfully roll back the rest of the set, should the guest be resumed (as if the command had never been attempted), or should the guest be left paused? On the other hand, if we fail at creating one snapshot, as well as fail at rolling back, then that argues that we _cannot_ resume the guest, because we no longer have a block device open. This policy needs to be documented in one (or both) of the two new monitor commands, and we probably ought to make sure that if the guest is left paused where it had originally started as running, then an appropriate event is also emitted. For blockdev-snapshot-sync, libvirt was always pausing qemu before issuing the snapshot, then resuming afterwards; but now that we have the ability to make the set atomic, I'm debating about whether libvirt still needs to pause qemu, or whether it can now rely on qemu doing the right things about pausing and resuming as part of the snapshot command. --=20 Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --------------enigC3BAAB10A6195EF785D41D30 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQEcBAEBCAAGBQJPQod4AAoJEKeha0olJ0NqlIoH/2IfYJ07NA00j9itea/0wtYd wSF5+0MRiLw/1I4DiiHlFjVNmnZQZkw7BdnuLNvSg0OItIRhht8CvoNpKbwoBbwA 9oKICKOFANxByRX3mj9RdibvGT2K8SkUT4+ibYEIVI7qoUZNIJTmdREsEJ8VSa1a Nmzwd+3PI7rseJQMaptHNJVezHTEHItKHb6qu8QUKe9OBwFmv2x/+7tXpReZpDVJ gbBj3GqVjdP84lxAUvaaZwheILVcF3QMnQdyuYlsAdvjc/smEzDUH9Qz1u6gzNfy wU74Fa6rhqqJIpn9hfrJkENX/71YhoheCWbKiNUv3dpPU4WLwdSpmx4MpueYBIc= =+uEo -----END PGP SIGNATURE----- --------------enigC3BAAB10A6195EF785D41D30--