On Tue, Oct 10, 2017 at 05:00:18PM +0200, Marc-André Lureau wrote: > Hi > > On Tue, Oct 10, 2017 at 10:31 AM, Daniel P. Berrange > <berra...@redhat.com> 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" <berra...@redhat.com> wrote: > >> > > > >> > > > On Mon, Sep 11, 2017 at 06:59:24PM +0200, Marc-André Lureau 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 > >> > > > misunderstanding, > >> > > > this doesn't feel like a device to me - its just a well known bucket > >> > > > in fw_cfg IIUC ? Obviously its existance would need to be tied 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 through to > >> > > > all the downstream applications that use QEMU for mgmt guest > >> > > > (OpenStack, > >> > > > oVirt, GNOME Boxes, virt-manager, and countless other mgmt apps). > >> > > 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 could be > >> > > just omitted > >> > > from CLI. > >> > > >> > Sure but it means that in effect no one will have this functionality > >> > enabled > >> > for several years. pvpanic has been around a long time and I rarely see > >> > it > >> > present in configured guests :-( > >> > > >> > > >> > Regards, > >> > Daniel > >> > >> libvirt runs with -nodefaults, right? I'd argue pretty strongly -nodefaults > >> 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. > > Enabling the device on some configurations by default can be done as a > follow-up patch. Can we get this series reviewed & merged?
The problem with the -device approach + turning it on by default is that 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 uses that already it would negate the effect of enabling it by default unconditionally. Your previous approach of "-global fw_cfg.vmcoreinfo=on" is nicer in this respect, as you can trivially turn it on/off, overriding the default state in both directions. 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 :|
