On Tue, Jun 05, 2018 at 02:51:52PM +0100, Daniel P. Berrangé wrote: > On Tue, Jun 05, 2018 at 03:44:14PM +0200, Laszlo Ersek wrote: > > On 06/05/18 15:29, Daniel P. Berrangé wrote: > > > On Tue, Jun 05, 2018 at 04:20:46PM +0300, Marcel Apfelbaum wrote: > > >> > > >> > > >> On 06/05/2018 11:43 AM, Daniel P. Berrangé 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 ...., select > > >> 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 to q35 > > >> the creation of new domains ? This way it aligns with Gerd's proposal of > > >> no > > >> default x86 machine. > > > > > > 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 q35 > > > 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. > > > > 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/2e7d477156e9d0f6fb218fa19fc00d6229d33e85/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.
Oh, that might be a nice thing to put into qcow2 meta-data. (Hopefully in a format that's easier to parse and write than xml). > > - write converters from those other definition formats to libvirt XML, > > or QEMU cfg file? > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
