On Fri, Aug 26, 2011 at 09:07:35AM -0500, Alexander Graf wrote: > On 26.08.2011, at 04:33, Roedel, Joerg wrote: > > > > The reason is that you mean the usability for the programmer and I mean > > it for the actual user of qemu :) > > No, we mean the actual user of qemu. The reason being that making a > device available for any user space application is an administrative > task. > > Forget the KVM case for a moment and think of a user space device > driver. I as a user am not root. But I as a user when having access to > /dev/vfioX want to be able to access the device and manage it - and > only it. The admin of that box needs to set it up properly for me to > be able to access it. Right, and that task is being performed by attaching the device(s) in question to the vfio driver. The rights-management happens on the /dev/vfio/$group file. > So having two steps is really the correct way to go: > > * create VFIO group > * use VFIO group > > because the two are done by completely different users. It's similar > to how tun/tap works in Linux too. Of course nothing keeps you from > also creating a group on the fly, but it shouldn't be the only > interface available. The persistent setup is definitely more useful. I see the use-case. But to make it as easy as possible for the end-user we can do both. So the user of (qemu again) does this: # vfio-ctl attach 00:01.0 vfio-ctl: attached to group 8 # vfio-ctl attach 00:02.0 vfio-ctl: attached to group 16 $ qemu -device vfio-pci,host=00:01.0 -device vfio,host=00:01.0 ... which should cover the usecase you prefer. Qemu still creates the meta-group that allow the devices to share the same page-table. But what should also be possible is: # qemu -device vfio-pci,host=00:01.0 -device vfio-pci,host=00:02.0 In that case qemu detects that the devices are not yet bound to vfio and will do so and also unbinds them afterwards (essentially the developer use-case). Your interface which requires pre-binding of devices into one group by the administrator only makes sense if you want to force userspace to use certain devices (which do not belong to the same hw-group) only together. But I don't see a usecase for defining such constraints (yet). Joerg -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
