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libvirt previously assigned nearly all devices to a "hotpluggable" legacy PCI slot even on machines with a PCIe root bus (and even though most such machines don't even support hotplug on legacy PCI slots!) Forcing all devices onto legacy PCI slots means that the domain will need a dmi-to-pci-bridge (to convert from PCIe to legacy PCI) and a pci-bridge (to provide hotpluggable legacy PCI slots which, again, usually aren't hotpluggable anyway). To help reduce the need for these legacy controllers, this patch tries to assign virtio-1.0-capable devices to PCIe slots whenever possible, by setting appropriate connectFlags in virDomainCalculateDevicePCIConnectFlags(). Happily, when that function was written (just a few commits ago) it was created with a "virtioFlags" argument, set by both of its callers, which is the proper connectFlags to set for any virtio-*-pci device - depending on the arch/machinetype of the domain, and whether or not the qemu binary supports virtio-1.0, that flag will have either been set to PCI or PCIe. This patch merely enables the functionality by setting the flags for the device to whatever is in virtioFlags if the device is a virtio-*-pci device. NB: the first virtio video device will be placed directly on bus 0 slot 1 rather than on a pcie-root-port due to the override for primary video devices in qemuDomainValidateDevicePCISlotsQ35(). Whether or not to change that is a topic of discussion, but this patch doesn't change that particular behavior. NB2: since the slot must be hotpluggable, and pcie-root (the PCIe root complex) does *not* support hotplug, this means that suitable controllers must also be in the config (i.e. either pcie-root-port, or pcie-downstream-port). For now, libvirt doesn't add those automatically, so if you put virtio devices in a config for a qemu that has PCIe-capable virtio devices, you'll need to add extra pcie-root-ports yourself. That requirement will be eliminated in a future patch, but for now, it's simple to do this: <controller type='pci' model='pcie-root-port'/> <controller type='pci' model='pcie-root-port'/> <controller type='pci' model='pcie-root-port'/> ... Partially Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1330024
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>