qmp: add QMP interface "query-cpu-model-baseline"

Let's provide a standardized interface to baseline two CPU models, to
create a third, compatible one. This is especially helpful when two
CPU models are not identical, but a CPU model is required that is
guaranteed to run under both configurations, where the original models run.

"query-cpu-model-baseline" takes two CPU models and returns a third,
compatible model. The result will always be a static CPU model.

Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Message-Id: <20160905085244.99980-28-dahi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>

qapi-schema.json

@@ -3244,6 +3244,57 @@
   'data': { 'modela': 'CpuModelInfo', 'modelb': 'CpuModelInfo' },
   'returns': 'CpuModelCompareInfo' }
 
+##
+# @CpuModelBaselineInfo
+#
+# The result of a CPU model baseline.
+#
+# @model: the baselined CpuModelInfo.
+#
+# Since: 2.8.0
+##
+{ 'struct': 'CpuModelBaselineInfo',
+  'data': { 'model': 'CpuModelInfo' } }
+
+##
+# @query-cpu-model-baseline:
+#
+# Baseline two CPU models, creating a compatible third model. The created
+# model will always be a static, migration-safe CPU model (see "static"
+# CPU model expansion for details).
+#
+# This interface can be used by tooling to create a compatible CPU model out
+# two CPU models. The created CPU model will be identical to or a subset of
+# both CPU models when comparing them. Therefore, the created CPU model is
+# guaranteed to run where the given CPU models run.
+#
+# The result returned by this command may be affected by:
+#
+# * QEMU version: CPU models may look different depending on the QEMU version.
+#   (Except for CPU models reported as "static" in query-cpu-definitions.)
+# * machine-type: CPU model  may look different depending on the machine-type.
+#   (Except for CPU models reported as "static" in query-cpu-definitions.)
+# * machine options (including accelerator): in some architectures, CPU models
+#   may look different depending on machine and accelerator options. (Except for
+#   CPU models reported as "static" in query-cpu-definitions.)
+# * "-cpu" arguments and global properties: arguments to the -cpu option and
+#   global properties may affect expansion of CPU models. Using
+#   query-cpu-model-expansion while using these is not advised.
+#
+# Some architectures may not support baselining CPU models.
+#
+# Returns: a CpuModelBaselineInfo. Returns an error if baselining CPU models is
+#          not supported, if a model cannot be used, if a model contains
+#          an unknown cpu definition name, unknown properties or properties
+#          with wrong types.
+#
+# Since: 2.8.0
+##
+{ 'command': 'query-cpu-model-baseline',
+  'data': { 'modela': 'CpuModelInfo',
+            'modelb': 'CpuModelInfo' },
+  'returns': 'CpuModelBaselineInfo' }
+
 # @AddfdInfo:
 #
 # Information about a file descriptor that was added to an fd set.