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When trying to assign a PCI device to a guest, we have to check that all bridges upstream of that device support ACS. That means that we have to find the parent bridge of the current device, check for ACS, then find the parent bridge of that device, check for ACS, etc. As it currently stands, the code to do this iterates through all PCI devices on the system, looking for a device that has a range of busses that included the current device's bus. That check is not restrictive enough, though. Depending on how we iterated through the list of PCI devices, we could first find the *topmost* bridge in the system; since it necessarily had a range of busses including the current device's bus, we would only ever check the topmost bridge, and not check any of the intermediate bridges. Note that this also caused a fairly serious bug in the secondary bus reset code, where we could erroneously find and reset the topmost bus instead of the inner bus. This patch changes pciGetParentDevice() so that it first checks if a bridge device's secondary bus exactly matches the bus of the device we are looking for. If it does, we've found the correct parent bridge and we are done. If it does not, then we check to see if this bridge device's busses *include* the bus of the device we care about. If so, we mark this bridge device as best, and go on. If we later find another bridge device whose busses include this device, but is more restrictive, then we free up the previous best and mark the new one as best. This algorithm ensures that in the normal case we find the direct parent, but in the case that the parent bridge secondary bus is not exactly the same as the device, we still find the correct bridge. This patch was tested by me on a 4-port NIC with a bridge without ACS (where assignment failed), a 4-port NIC with a bridge with ACS (where assignment succeeded), and a 2-port NIC with no bridges (where assignment succeeded). Signed-off-by: Chris Lalancette <clalance@redhat.com>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>