From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33485) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fQCNU-0003Fx-RE for qemu-devel@nongnu.org; Tue, 05 Jun 2018 09:52:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fQCNR-0006Wc-KU for qemu-devel@nongnu.org; Tue, 05 Jun 2018 09:52:00 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:46732 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fQCNR-0006WL-DW for qemu-devel@nongnu.org; Tue, 05 Jun 2018 09:51:57 -0400 Date: Tue, 5 Jun 2018 14:51:52 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Message-ID: <20180605135152.GJ32286@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20180603092749.107476-1-marcel.apfelbaum@gmail.com> <20180604042928-mutt-send-email-mst@kernel.org> <23040757-b561-e0bf-a41d-38d3c44555ee@gmail.com> <20180605072746.v6xxabsbewiuw7ka@sirius.home.kraxel.org> <20180605084300.GF32286@redhat.com> <53c37321-52d2-732c-19fb-8f6a9542c714@gmail.com> <20180605132948.GH32286@redhat.com> <5f7fad87-73dd-ef75-bb1d-983d36e42073@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <5f7fad87-73dd-ef75-bb1d-983d36e42073@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH RFC] hw/pc: set q35 as the default x86 machine List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Laszlo Ersek Cc: Marcel Apfelbaum , ehabkost@redhat.com, "Michael S. Tsirkin" , qemu-devel@nongnu.org, Gerd Hoffmann , pbonzini@redhat.com, rth@twiddle.net On Tue, Jun 05, 2018 at 03:44:14PM +0200, Laszlo Ersek wrote: > On 06/05/18 15:29, Daniel P. Berrang=C3=A9 wrote: > > On Tue, Jun 05, 2018 at 04:20:46PM +0300, Marcel Apfelbaum wrote: > >> > >> > >> On 06/05/2018 11:43 AM, Daniel P. Berrang=C3=A9 wrote: > >>> On Tue, Jun 05, 2018 at 09:27:46AM +0200, Gerd Hoffmann wrote: > >>>> Hi, > >>>> > >>>>>> Add to that shortcuts like -cdrom > >>>>>> stop working, > >>>>> Maybe is fixable. > >>>> Already fixed for ages. > >>>> > >>>>> I see marking Q35 as the default machine a first step. > >>>> Maybe the better option is to go the arm route: Just don't define= a > >>>> default, so users have to specify pc or q35. That will make them = notice > >>>> there is a world beside 'pc', and we also avoid breaking things > >>>> silently. > >> > >> It can work, sure. And we can add user hints: "Use q35 for ...., sel= ect pc > >> if..." > >> > >>> If QEMU removes the default, then libvirt will have to hardcode > >>> 'pc' as the default to maintain back compatibility, so I don't > >>> think that ends up as a net win > >> > >> Can't libvirt preserve 'pc' for existing domains, while defaulting t= o q35 > >> the creation of new domains ? This way it aligns with Gerd's proposa= l of no > >> default x86 machine. > >=20 > > Existing domains wasn't the case I was concerned about. Consider you = have > > libvirt 4.4.0 intsalled and you deploy a *new* domain from a prebuilt > > disk image "foo". Now update to a libvirt or QEMU which changes to q3= 5 > > and try to deploy another new domain from the same prebuilt disk > > image "foo". It may not work now if that disk image doesn't support > > q35. That would be a regression from the user's POV, whether libvirt = or > > qemu has changed the default. >=20 > How about: > - "create new domain with empty disk" --> i440fx now, q35 later "empty disk" is not something that can be determined by the host - libvirt might not even have direct access to the disk at the time this info would be needed. > - "create new domain from domain XML and disk image" --> whatever the > domain definition dictates > - "create new domain from disk image and no domain XML" --> assume > i440fx forever (with a detailed board / device config that's used for > all legacy (definition-less) disk images) > - convince disk image distributors to provide their domain definitions > with their disks (need not be libvirt domain XML, other definitions > might work) Libvirt domain XML is absolutely not suitable - it is a host specific instantiation of a guest, that is not guaranteed to be portable to any other host. Funnily enough though, I just remembered that 10 years ago we invented another XML format called "virt-image XML", that went along with a "virt-image" command line tool https://github.com/virt-manager/virt-manager/blob/2e7d477156e9d0f6fb218= fa19fc00d6229d33e85/man/virt-image-xml.pod This was rarely used because the "virt-image" tool itself was rather broken by design, so we eventually deleted this entirely. The virt-image XML description though could be resurrected as it is largely relevant to the conversation. > - write converters from those other definition formats to libvirt XML, > or QEMU cfg file? Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|