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Previously libvirt would only add pci-bridge devices automatically when an address was requested for a device that required a legacy PCI slot and none was available. This patch expands that support to dmi-to-pci-bridge (which is needed in order to add a pci-bridge on a machine with a pcie-root), and pcie-root-port (which is needed to add a hotpluggable PCIe device). It does *not* automatically add pcie-switch-upstream-ports or pcie-switch-downstream-ports (and currently there are no plans for that). Given the existing code to auto-add pci-bridge devices, automatically adding pcie-root-ports is fairly straightforward. The dmi-to-pci-bridge support is a bit tricky though, for a few reasons: 1) Although the only reason to add a dmi-to-pci-bridge is so that there is a reasonable place to plug in a pci-bridge controller, most of the time it's not the presence of a pci-bridge *in the config* that triggers the requirement to add a dmi-to-pci-bridge. Rather, it is the presence of a legacy-PCI device in the config, which triggers auto-add of a pci-bridge, which triggers auto-add of a dmi-to-pci-bridge (this is handled in virDomainPCIAddressSetGrow() - if there's a request to add a pci-bridge we'll check if there is a suitable bus to plug it into; if not, we first add a dmi-to-pci-bridge). 2) Once there is already a single dmi-to-pci-bridge on the system, there won't be a need for any more, even if it's full, as long as there is a pci-bridge with an open slot - you can also plug pci-bridges into existing pci-bridges. So we have to make sure we don't add a dmi-to-pci-bridge unless there aren't any dmi-to-pci-bridges *or* any pci-bridges. 3) Although it is strongly discouraged, it is legal for a pci-bridge to be directly plugged into pcie-root, and we don't want to auto-add a dmi-to-pci-bridge if there is already a pci-bridge that's been forced directly into pcie-root. Although libvirt will now automatically create a dmi-to-pci-bridge when it's needed, the code still remains for now that forces a dmi-to-pci-bridge on all domains with pcie-root (in qemuDomainDefAddDefaultDevices()). That will be removed in a future patch. For now, the pcie-root-ports are added one to a slot, which is a bit wasteful and means it will fail after 31 total PCIe devices (30 if there are also some PCI devices), but helps keep the changeset down for this patch. A future patch will have 8 pcie-root-ports sharing the functions on a single slot.
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>