On Tue, May 27, 2014 at 09:07:42PM -0600, Bjorn Helgaas wrote: > On Tue, May 20, 2014 at 08:53:21AM -0600, Alex Williamson wrote: > > The driver_override field allows us to specify the driver for a device > > rather than relying on the driver to provide a positive match of the > > device. This shortcuts the existing process of looking up the vendor > > and device ID, adding them to the driver new_id, binding the device, > > then removing the ID, but it also provides a couple advantages. > > > > First, the above existing process allows the driver to bind to any > > device matching the new_id for the window where it's enabled. This is > > often not desired, such as the case of trying to bind a single device > > to a meta driver like pci-stub or vfio-pci. Using driver_override we > > can do this deterministically using: > > > > echo pci-stub > /sys/bus/pci/devices/0000:03:00.0/driver_override > > echo 0000:03:00.0 > /sys/bus/pci/devices/0000:03:00.0/driver/unbind > > echo 0000:03:00.0 > /sys/bus/pci/drivers_probe > > > > Previously we could not invoke drivers_probe after adding a device > > to new_id for a driver as we get non-deterministic behavior whether > > the driver we intend or the standard driver will claim the device. > > Now it becomes a deterministic process, only the driver matching > > driver_override will probe the device. > > > > To return the device to the standard driver, we simply clear the > > driver_override and reprobe the device: > > > > echo > /sys/bus/pci/devices/0000:03:00.0/driver_override > > echo 0000:03:00.0 > /sys/bus/pci/devices/0000:03:00.0/driver/unbind > > echo 0000:03:00.0 > /sys/bus/pci/drivers_probe > > > > Another advantage to this approach is that we can specify a driver > > override to force a specific binding or prevent any binding. For > > instance when an IOMMU group is exposed to userspace through VFIO > > we require that all devices within that group are owned by VFIO. > > However, devices can be hot-added into an IOMMU group, in which case > > we want to prevent the device from binding to any driver (override > > driver = "none") or perhaps have it automatically bind to vfio-pci. > > With driver_override it's a simple matter for this field to be set > > internally when the device is first discovered to prevent driver > > matches. > > > > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > Greg, are you going to weigh in on this? It does seem to solve some real > problems. ISTR you had an opinion once, but I don't know your current > thoughts. This looks good to me: Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list