On Fri, Mar 24, 2017 at 01:49:16PM +0300, Marcel Apfelbaum wrote: > On 03/22/2017 10:46 PM, Laszlo Ersek wrote: > > On 03/22/17 21:31, Eduardo Habkost wrote: > > > Hi, > > > > > > I am investigating the current status of has_dynamic_sysbus and > > > sysbus device support on each of QEMU's machine types. The good > > > news is that almost all has_dynamic_sysbus=1 machines have their > > > own internal (often short) whitelist of supported sysbus device > > > types, and automatically reject unsupported devices. > > > > > > ...except for q35. > > > > > > q35 currently accepts all sys-bus-device subtypes on "-device", > > > and today this includes the following 23 devices: > > > > > > * allwinner-ahci > > > * amd-iommu > > > * cfi.pflash01 > > > * esp > > > * fw_cfg_io > > > * fw_cfg_mem > > > * generic-sdhci > > > * hpet > > > * intel-iommu > > > * ioapic > > > * isabus-bridge > > > * kvmclock > > > * kvm-ioapic > > > * kvmvapic > > > * SUNW,fdtwo > > > * sysbus-ahci > > > * sysbus-fdc > > > * sysbus-ohci > > > * unimplemented-device > > > * virtio-mmio > > > * xen-backend > > > * xen-sysdev > > > > > > My question is: do all those devices really make sense to be used > > > with "-device" on q35? > > > > I think fw_cfg_io and fw_cfg_mem should be board-only devices (no > > -device switch). > > > > Regarding cfi.pflash01, I think originally it would have been nice to > > specify pflash chips with the modern (non-legacy) syntax, that is, > > separate -drive if=none,file=... backend options combined with -device > > cfi.pflash01,drive=... frontend options. However, that ship has sailed, > > even libvirt uses -drive if=pflash for these, and given the purpose we > > use pflash chips for, on Q35, I don't see much benefit in exposing > > cfi.pflash01 with a naked -device *now*. > > > > Re: virtio-mmio, I don't think that should be available on Q35 at all. > > > > I can't comment on the rest. > > > > Hi Eduardo, > Thanks for finding these problems. > > We should ping all maintainers of the above devices, the best way to do it > is to add the "cannot_instantiate_with_device_add_yet = true" and ask > maintainers > to agree (or not) on that.
If I understand it correctly, cannot_instantiate_with_device_add_yet is supposed to be temporary. And it applies to all machines, with no exceptions. The problem with today's mechanism is that we have no way to make a machine accept one type of sysbus device without making it start accepting every other sysbus devices. If we thought all !cannot_instantiate_with_device_add_yet sysbus devices were already safe, we wouldn't have has_dynamic_sysbus in the first place, would we? -- Eduardo
