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.
Does it mean every time we make a PC device configurable, we should make it be disabled by -nodefaults, and require libvirt to adapt? I don't think that would be a good idea. Imagine the hassle the "pc: make .* configurable" patches[1] would generate for libvirt. > > So it's up to you guys, you can add it to VMs by default if you want to. To be honest, I think "no defaults" is a misleading name for an option. If it really meant "create no optional device at all", it would eventually become a synonym for "-machine none", and I don't think that's its goal. I expect PC to always have a set of devices/features that are disabled by -nodefaults, and a set of devices/features that are not disabled by -nodefaults. We need good judgement to decide on which set the device will be, and I believe Daniel exposed good arguments to put vmcoreinfo in the second set. [1] https://www.mail-archive.com/qemu-devel@nongnu.org/msg393493.html Subject: [RFC PATCH v2 00/12] Guest startup time optimization -- Eduardo
