On 04/16/2014 09:40 AM, Andy Lutomirski wrote: >> USB has always been off by default, at least for the boards I'm familiar >> with, due to the USB emulation's non-trivial CPU use. >> >> There's no such thing as a Q35 board without USB in the physical world. >> Can't stop us from making a virtual one, of course. >> >> Likewise, there's no such thing as a Q35 board without AHCI in the >> physical world, and again that can't stop us from making a virtual one. >> >> The difference to USB is that our q35 machines have always had AHCI even >> with -nodefaults. You seem to propose adding a switch to disable AHCI, >> yet leave it enabled with -nodefaults. >> >> -nodefaults should give you a board with all the optional components >> suppressed. > > Will this break libvirt, which may expect -nodefaults to still come > with an IDE bus?
Libvirt can be taught to deal with whatever default devices are present vs. mising according to -nodefaults; although the IDEAL situation is that there would be some QMP command for querying what devices are present when -nodefaults is used, so that libvirt can reliably supply all remaining devices. As long as there is a way to tell between older qemu that always supplied AHCI and your proposed newer qemu that omits it for -nodefaults, libvirt should be fine with this proposal. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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