From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34436) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e1yqE-00027Q-Lw for qemu-devel@nongnu.org; Tue, 10 Oct 2017 14:01:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1e1yqB-0005FH-IE for qemu-devel@nongnu.org; Tue, 10 Oct 2017 14:01:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36268) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1e1yqB-0005F4-9v for qemu-devel@nongnu.org; Tue, 10 Oct 2017 14:01:15 -0400 Date: Tue, 10 Oct 2017 15:01:10 -0300 From: Eduardo Habkost Message-ID: <20171010180110.GI3246@localhost.localdomain> References: <20170911165929.2791-1-marcandre.lureau@redhat.com> <20170911165929.2791-3-marcandre.lureau@redhat.com> <20171009110336.GA17824@redhat.com> <20171009144344.38bbd1e9@nial.brq.redhat.com> <20171009130218.GK2954@redhat.com> <20171010003951-mutt-send-email-mst@kernel.org> <20171010083143.GA30015@redhat.com> <20171010150628.GI30015@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20171010150628.GI30015@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v6 2/7] hw/misc: add vmcoreinfo device List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , "Michael S. Tsirkin" , QEMU , Dave Anderson , Igor Mammedov , Laszlo Ersek On Tue, Oct 10, 2017 at 04:06:28PM +0100, Daniel P. Berrange wrote: > On Tue, Oct 10, 2017 at 05:00:18PM +0200, Marc-Andr=E9 Lureau wrote: > > Hi > >=20 > > On Tue, Oct 10, 2017 at 10:31 AM, Daniel P. Berrange > > wrote: > > > On Tue, Oct 10, 2017 at 12:44:26AM +0300, Michael S. Tsirkin wrote: > > >> On Mon, Oct 09, 2017 at 02:02:18PM +0100, Daniel P. Berrange wrote= : > > >> > On Mon, Oct 09, 2017 at 02:43:44PM +0200, Igor Mammedov wrote: > > >> > > On Mon, 9 Oct 2017 12:03:36 +0100 > > >> > > "Daniel P. Berrange" wrote: > > >> > > > > >> > > > On Mon, Sep 11, 2017 at 06:59:24PM +0200, Marc-Andr=E9 Lurea= u wrote: > > >> > > > > See docs/specs/vmcoreinfo.txt for details. > > >> > > > > > > >> > > > > "etc/vmcoreinfo" fw_cfg entry is added when using "-device= vmcoreinfo". > > >> > > > > > >> > > > I'm wondering if you considered just adding the entry to fw_= cfg by > > >> > > > default, without requiring any -device arg ? Unless I'm misu= nderstanding, > > >> > > > this doesn't feel like a device to me - its just a well know= n bucket > > >> > > > in fw_cfg IIUC ? Obviously its existance would need to be t= ied to > > >> > > > the latest machine type for ABI reasons though. The benefit = of this > > >> > > > is that it would "just work" without us having to plumb it t= hrough to > > >> > > > all the downstream applications that use QEMU for mgmt guest= (OpenStack, > > >> > > > oVirt, GNOME Boxes, virt-manager, and countless other mgmt a= pps). > > >> > > it follows model set by pvpanic device, it's easier to manage = from migration > > >> > > POV, one could use it even for old machine types with new qemu= (just by adding > > >> > > device, it makes instance not backwards migratable to old qemu= but should work > > >> > > for forward migration) and if user doesn't need it, device cou= ld be just omitted > > >> > > from CLI. > > >> > > > >> > Sure but it means that in effect no one will have this functiona= lity enabled > > >> > for several years. pvpanic has been around a long time and I rar= ely see it > > >> > present in configured guests :-( > > >> > > > >> > > > >> > Regards, > > >> > Daniel > > >> > > >> libvirt runs with -nodefaults, right? I'd argue pretty strongly -n= odefaults > > >> shouldn't add optional devices anyway. > > > > > > This isn't really adding a device though is it - it is just a well = known > > > location in fw_cfg to receive data. > >=20 > > Enabling the device on some configurations by default can be done as = a > > follow-up patch. Can we get this series reviewed & merged? >=20 > The problem with the -device approach + turning it on by default is tha= t there > is no way to turn it off again if you don't want it. eg there's way to = undo > an implicit '-device foo' except via -nodefaults, but since libvirt use= s that > already it would negate the effect of enabling it by default unconditio= nally. It's still possible to add a -machine option that can enable/disable automatic creation of the device. But I also don't see why it needs to be implemented using -device if it's not really a device. A boolean machine or fw_cfg property is good enough for that. >=20 > Your previous approach of "-global fw_cfg.vmcoreinfo=3Don" is nicer in = this > respect, as you can trivially turn it on/off, overriding the default st= ate > in both directions. Both "-global fw_cfg.vmcoreinfo=3Don|off" and "-machine vmcoreinfo=3Don|off" sound good enough to me. --=20 Eduardo