From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:45360) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UV2UN-0006n2-SI for qemu-devel@nongnu.org; Wed, 24 Apr 2013 12:24:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UV2UJ-0006Hv-2H for qemu-devel@nongnu.org; Wed, 24 Apr 2013 12:24:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:14472) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UV2UI-0006Hp-Pl for qemu-devel@nongnu.org; Wed, 24 Apr 2013 12:24:06 -0400 Message-ID: <5178071E.7020908@redhat.com> Date: Wed, 24 Apr 2013 10:23:58 -0600 From: Eric Blake MIME-Version: 1.0 References: <1366731014-48790-1-git-send-email-jfrei@linux.vnet.ibm.com> <1366731014-48790-2-git-send-email-jfrei@linux.vnet.ibm.com> <5176ABB7.8080102@redhat.com> <20130424115022.2ac2667d@redhat.com> In-Reply-To: <20130424115022.2ac2667d@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="----enig2BSAURRUOHGFBWARKKGVG" Subject: Re: [Qemu-devel] [PATCH 1/2] Split out dump-guest-memory memory mapping code List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Luiz Capitulino Cc: Peter Maydell , Ekaterina Tumanova , Alexander Graf , qemu-devel , Rabin Vincent , Christian Borntraeger , Jens Freimann , Paolo Bonzini , =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= This is an OpenPGP/MIME signed message (RFC 4880 and 3156) ------enig2BSAURRUOHGFBWARKKGVG Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 04/24/2013 09:50 AM, Luiz Capitulino wrote: >> This raises an interesting question about introspection - how will >> management apps (such as libvirt) be able to determine whether the >> paging command is supported for a given architecture? Do we need to >> expand the 'MachineInfo' QMP datatype so that 'query-machines' can tel= l >> us whether a given machine will support or reject attempts to set >> 'paging':true during 'dump-guest-memory'? >=20 > Is libvirt going to query this for the automatic dump feature? Probably. Right now, libvirt has already exposed the paging option to users, and uses the try-and-fail approach of reporting back any error message from QMP if the dump command fails. But we've had error reports in the past against libvirt that the error reported by qemu isn't always the sanest, and that sometimes it is much nicer to have libvirt detect in advance that a qemu command cannot succeed than it is to do a try-and-fail approach. There's also a matter of clean rollbacks; libvirt has to set up some state when starting a dump command, and has to undo that state if try-and-fail reported an error; whereas a capability detection can avoid having to set up any state in the first place. >=20 > I'm asking this because if the fact that an arch doesn't support memory= > dump is only visible to human users, then try & fail doesn't seem bad. Introspection can't hurt, even if libvirt doesn't use it right away. It may be the sort of thing where we commit the initial capability with try-and-fail handling, then down the road, decide whether the error quality is good enough; it also seems like introspection is the sort of thing that is easy to backport, even if the introspection does not go in at the same time as the original feature, where improved error messages becomes a quality-of-implementation value-added by distro packagers. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org ------enig2BSAURRUOHGFBWARKKGVG 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/ iQEcBAEBCAAGBQJReAceAAoJEKeha0olJ0NqZg0H/2kyXyFCfx6uWu/K/9KbW96y ox5Es2yD6M/iQhwA1K7tj6IQiG+Bb9YrwJsB6BTVU/H98gkCQWOzB8pQHAZ6EYAw hr11j+Y+devANNsqghl1ogo+2o4pNFgWkNMwO1mi5KO7sctghQY79Mthe+pecy2U wlmhZ8yNm4KbImNc1s5hu/MH9V2EuCwIqmniGvuFxPWQFezrTtqAe3n2u2hsvVr5 qY5lIhcvBBHZHrAHDxaFDsaG1+FY0nlg20DfC9OscXz1Y0J0CamnzSF2+rIyWGDv /LGEes5DDlhv25NrZUyacFqZVSmfatIEr+1A6MRsaxPWrVtqkYdmfSZXiCf5WEw= =2AbV -----END PGP SIGNATURE----- ------enig2BSAURRUOHGFBWARKKGVG--