[Libvir] PATCH 0/2: Capabilities and features

[David Lutterkort]

Hi,

these two patches extend the features libvirt reports in the
capabilities XML; in particular, features are now reported for the QEMU
driver, and features for both Xen and QEMU include information on
ACPI/APIC support.

Tools that rely on feature reporting, in general, need to know whether a
certain feature is on or off by default, and whether that can be
toggled, because users will be asking for one of three things for their
VM:

      * Feature X (e.g., ACPI) must be on/present in the VM
      * Feature X must not be on/present in the VM
      * It doesn't matter whether feature X is there or not

For example, in QEMU, ACPI is on by default, but can be turned off. The
APIC on the other hand, is always there and can't be turned off. That is
now reported as

            <features>
              <acpi default="on" toggle="yes"/>
              <apic default="on" toggle="no"/>
            </features>

It's unfortunate that the format for PAE (<pae/> vs. <nonpae/>)
reporting doesn't fit into this scheme. I didn't want to start with
having tags <X/> and <nonX/> for each feature; that means that parsers
need to special case PAE. It's probably too late, but it would be nice
if PAE was reported in a similar format, with <pae> correponding to <pae
default="on" toggle="no"/>, <nonpae/> corresponding to <pae
default="yes" toggle="no"/>, and having both together corresponding to
<pae default="yes" toggle="yes"/>, but that's a separate discussion from
these patches.

David