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62ac6b4354
This PCI controller, named "dmi-to-pci-bridge" in the libvirt config, and implemented with qemu's "i82801b11-bridge" device, connects to a PCI Express slot (e.g. one of the slots provided by the pcie-root controller, aka "pcie.0" on the qemu commandline), and provides 31 *non-hot-pluggable* PCI (*not* PCIe) slots, numbered 1-31. Any time a machine is defined which has a pcie-root controller (i.e. any q35-based machinetype), libvirt will automatically add a dmi-to-pci-bridge controller if one doesn't exist, and also add a pci-bridge controller. The reasoning here is that any useful domain will have either an immediate (startup time) or eventual (subsequent hot-plug) need for a standard PCI slot; since the pcie-root controller only provides PCIe slots, we need to connect a dmi-to-pci-bridge controller to it in order to get a non-hot-plug PCI slot that we can then use to connect a pci-bridge - the slots provided by the pci-bridge will be both standard PCI and hot-pluggable. Since pci-bridge devices themselves can not be hot-plugged into a running system (although you can hot-plug other devices into a pci-bridge's slots), any new pci-bridge controller that is added can (and will) be plugged into the dmi-to-pci-bridge as long as it has empty slots available. This patch is also changing the qemuxml2xml-pcie test from a "DO_TEST" to a "DO_DIFFERENT_TEST". This is so that the "before" xml can omit the automatically added dmi-to-pci-bridge and pci-bridge devices, and the "after" xml can include it - this way we are testing if libvirt is properly adding these devices.
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>