XML schema for CPU flags
Firstly, CPU topology and model with optional features have to be
advertised in host capabilities:
<host>
<cpu>
<arch>ARCHITECTURE</arch>
<features>
<!-- old-style features are here -->
</features>
<model>NAME</model>
<topology sockets="S" cores="C" threads="T"/>
<feature name="NAME"/>
</cpu>
...
</host>
Secondly, drivers which support detailed CPU specification have to
advertise
it in guest capabilities:
<guest>
...
<features>
<cpuselection/>
</features>
</guest>
And finally, CPU may be configured in domain XML configuration:
<domain>
...
<cpu match="MATCH">
<model>NAME</model>
<topology sockets="S" cores="C" threads="T"/>
<feature policy="POLICY" name="NAME"/>
</cpu>
</domain>
Where MATCH can be one of:
- 'minimum' specified CPU is the minimum requested CPU
- 'exact' disable all additional features provided by host CPU
- 'strict' fail if host CPU doesn't exactly match
POLICY can be one of:
- 'force' turn on the feature, even if host doesn't have it
- 'require' fail if host doesn't have the feature
- 'optional' match host
- 'disable' turn off the feature, even if host has it
- 'forbid' fail if host has the feature
'force' and 'disable' policies turn on/off the feature regardless of its
availability on host. 'force' is unlikely to be used but its there for
completeness since Xen and VMWare allow it.
'require' and 'forbid' policies prevent a guest from being started on a host
which doesn't/does have the feature. 'forbid' is for cases where you disable
the feature but a guest may still try to access it anyway and you don't want
it to succeed.
'optional' policy sets the feature according to its availability on host.
When a guest is booted on a host that has the feature and then migrated to
another host, the policy changes to 'require' as we can't take the feature
away from a running guest.
Default policy for features provided by host CPU but not specified in domain
configuration is set using match attribute of cpu tag. If 'minimum' match is
requested, additional features will be treated as if they were specified
with 'optional' policy. 'exact' match implies 'disable' policy and 'strict'
match stands for 'forbid' policy.
* docs/schemas/capability.rng docs/schemas/domain.rng: extend the
RelaxNG schemas to add CPU flags support
e.g. <machine canonical='pc'>pc-0.11</machine>
* src/capabilities.c: output the canonical machine names in the
capabilities output, if available
* docs/schemas/capabilities.rng: add the new attribute
by running this command:
git ls-files -z | xargs -0 perl -pi -0777 -e 's/\n\n+$/\n/'
This is in preparation for a more strict make syntax-check
rule that will detect trailing blank lines.
