XenServer Software Development Kit Guide 4.1.0

XenServer API extensions

• The device /dev/xen/evtchn, which is accessed via xs_evtchn_open() in libxenctrl. A han-

dle can be restricted using xs_evtchn_restrict().

• The device /proc/xen/privcmd, accessed through xs_interface_open() in libxenctrl. A

handle is restricted using xc_interface_restrict(). Some privileged commands are naturally

hard to restrict (e.g. the ability to make arbitrary hypercalls), and these are simply prohibited on restricted

handles.

• A restricted handle cannot later be granted more privilege, and so the interface must be closed and re-

opened. Security is only gained if the process cannot subsequently open more handles.

• The qemu device emulation processes and vncterm terminal emulation processes run as a non-root

user ID and are restricted into an empty directory. They uses the restriction API above to drop privileges

where possible.

• Access to xenstore is rate-limited to prevent malicious guests from causing a denial of service on the

control domain. This is implemented as a token bucket with a restricted fill-rate, where most operations

take one token and opening a transaction takes 20. The limits are set high enough that they should never

be hit when running even a large number of concurrent guests under loaded operation.

• The VNC guest consoles are bound only to the localhost interface, so that they are not exposed

externally even if the control domain packet filter is disabled by user intervention.

5.5. Advanced settings for network interfaces

Virtual and physical network interfaces have some advanced settings that can be configured using the oth-

er-config map parameter. There are a set of custom ethtool settings and some miscellaneous settings.

5.5.1. ethtool settings

Developers might wish to configure custom ethtool settings for physical and virtual network interfaces. This

is accomplished with ethtool-<option> keys via the other-config map parameter.

Key Description Valid settings

ethtool-rx Specify if RX checksumming is enabled on or true to enable the