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PCIO device assignment using VFIO requires read/write access by the qemu process to /dev/vfio/vfio, and /dev/vfio/nn, where "nn" is the VFIO group number that the assigned device belongs to (and can be found with the function virPCIDeviceGetVFIOGroupDev) /dev/vfio/vfio can be accessible to any guest without danger (according to vfio developers), so it is added to the static ACL. The group device must be dynamically added to the cgroup ACL for each vfio hostdev in two places: 1) for any devices in the persistent config when the domain is started (done during qemuSetupCgroup()) 2) at device attach time for any hotplug devices (done in qemuDomainAttachHostDevice) The group device must be removed from the ACL when a device it "hot-unplugged" (in qemuDomainDetachHostDevice()) Note that USB devices are already doing their own cgroup setup and teardown in the hostdev-usb specific function. I chose to make the new functions generic and call them in a common location though. We can then move the USB-specific code (which is duplicated in two locations) to this single location. I'll be posting a followup patch to do that.
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>