You can use the Oracle VM Server for SPARC software to assign an entire PCIe bus (also known as a root complex) to a domain. An entire PCIe bus consists of the PCIe bus itself and all of its PCI switches and devices. PCIe buses that are present on a server are identified with names such as pci@400 (pci_0). An I/O domain that is configured with an entire PCIe bus is also known as a root domain.
The following diagram shows a system that has two root complexes, pci_0 and pci_1.
Figure 6-1 Assigning a PCIe Bus to an I/O Domain
The maximum number of I/O domains that you can create with PCIe buses depends on the number of PCIe buses that are available on the server. For example, if you are using an Oracle Sun SPARC Enterprise T5440 server, you can have up to four I/O domains.
When you assign a PCIe bus to an I/O domain, all devices on that bus are owned by that I/O domain. You can assign any of the PCIe endpoint devices on that bus to other domains.
When a server is initially configured in an Oracle VM Server for SPARC environment or is using the factory-default configuration, the primary domain has access to all the physical device resources. Therefore, the primary domain is the only I/O domain configured on the system and it owns all the PCIe buses.