Re: [libvirt] [PATCH v3] PCI: Introduce new device binding path using pci_dev.driver_override

Laine Stump
2014-05-22T13:36:24Z

On 05/20/2014 05:53 PM, 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

I'm not qualified to review the mechanics of the patch, but as a
potential consumer of this new interface (in libvirt), I want to say
that it is *immensely* improved over the racy, error prone method that
the kernel currently has available. The first day that I looked at the
libvirt code that uses the "new_id" method to bind drivers to devices, I
wished that there would instead be an interface more or less identical
to what Alex has described here - simple, deterministic, and with
minimal side effect outside of the exact device and driver pair we want
to bind.