IO privileges can be assigned to allow a domain to drive PCI devices
itself. This is used for to support driver domains.
+Setting backend privileges is currently only supported in SXP format
+config files (??? is this true - there's nothing in xmdefaults,
+anyhow). To allow a domain to function as a backend for others,
+somewhere within the {\tt vm} element of its configuration file must
+be a {\tt backend} element of the form {\tt (backend ({\em type}))}
+where {\tt \em type} may be either {\tt netif} or {\tt blkif},
+according to the type of virtual device this domain will service.
+After this domain has been built, Xend will connect all new and
+existing {\em virtual} devices (of the appropriate type) to that
+backend.
+
+Note that:
+\begin{itemize}
+\item a block backend cannot import virtual block devices from other
+domains
+\item a network backend cannot import virtual network devices from
+other domains
+\end{itemize}
+
+Thus (particularly in the case of block backends, which cannot import
+a virtual block device as their root filesystem), you may need to boot
+a backend domain from a ramdisk or a network device.
+
+The privilege to drive PCI devices may also be specified on a
+per-device basis. Xen will assign the minimal set of hardware
+privileges to a domain that are required to control its devices. This
+can be configured in either format of configuration file:
+
+\begin{itemize}
+\item SXP Format:
+ Include {\tt device} elements
+ {\tt (device (pci (bus {\em x}) (dev {\em y}) (func {\em z}))) } \\
+ inside the top-level {\tt vm} element. Each one specifies the address
+ of a device this domain is allowed to drive ---
+ the numbers {\em x},{\em y} and {\em z} may be in either decimal or
+ hexadecimal format.
+\item Flat Format: Include a list of PCI device addresses of the
+ format: \\ {\tt pci = ['x,y,z', ...] } \\ where each element in the
+ list is a string specifying the components of the PCI device
+ address, separated by commas. The components ({\tt \em x}, {\tt \em
+ y} and {\tt \em z}) of the list may be formatted as either decimal
+ or hexadecimal.
+\end{itemize}
+
\section{Administration Domains}
Administration privileges allow a domain to use the ``dom0
not need to be hidden --- they are hidden implicitly, since guest OSes
do not need to configure them.
+\chapter{Further Support}
+
+If you have questions that are not answered by this manual, the
+sources of information listed below may be of interest to you. Note
+that bug reports, suggestions and contributions related to the
+software (or the documentation) should be sent to the Xen developers'
+mailing list (address below).
+
+\section{Other documentation}
+
+For developers interested in porting operating systems to Xen, the
+{\em Xen Interface Manual} is distributed in the \path{docs/}
+directory of the Xen source distribution.
+
+\section{Online references}
+
+The official Xen web site is found at: \\
+{\tt
+http://www.cl.cam.ac.uk/Research/SRG/netos/xen/] }.
+
+Links to other
+documentation sources are listed at: \\ {\tt
+http://www.cl.cam.ac.uk/Research/SRG/netos/xen/documentation.html}.
+
+\section{Mailing lists}
+
+There are currently two official Xen mailing lists:
+
+\begin{description}
+\item[xen-devel@lists.sourceforge.net] Used for development
+discussions and requests for help. Subscribe at: \\
+http://lists.sourceforge.net/mailman/listinfo/xen-devel
+\item[xen-announce@lists.sourceforge.net] Used for announcements only.
+Subscribe at: \\ http://lists.sourceforge.net/mailman/listinfo/xen-announce
+\end{description}
+
+Although there is no specific user support list, the developers try to
+assist users who post on xen-devel. As the bulk of traffic on this
+list increases, a dedicated user support list may be introduced.
+
\end{document}
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