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

Let's provide a standardized interface to compare two CPU models.
"query-cpu-model-compare" takes two models and returns  how they compare
in a specific configuration.

The result will give guarantees about runnability. E.g. if a CPU model A
is a subset of CPU model B, model A is guaranteed to run in configurations
where model B runs, but not the other way around (might or might not run).

Usually, CPU features or CPU generations are used to calculate the result.
If a model is not guaranteed to run in a certain environment (e.g.
incompatible), a  compatible one can be created by "baselining" both models
(follow up patch).

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: <20160905085244.99980-27-dahi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>

include/sysemu/arch_init.h

@@ -38,5 +38,8 @@ CpuDefinitionInfoList *arch_query_cpu_definitions(Error **errp);
 CpuModelExpansionInfo *arch_query_cpu_model_expansion(CpuModelExpansionType type,
                                                       CpuModelInfo *mode,
                                                       Error **errp);
+CpuModelCompareInfo *arch_query_cpu_model_comparison(CpuModelInfo *modela,
+                                                     CpuModelInfo *modelb,
+                                                     Error **errp);
 
 #endif

qapi-schema.json

@@ -3158,6 +3158,92 @@
             'model': 'CpuModelInfo' },
   'returns': 'CpuModelExpansionInfo' }
 
+##
+# @CpuModelCompareResult:
+#
+# An enumeration of CPU model comparation results. The result is usually
+# calcualted using e.g. CPU features or CPU generations.
+#
+# @incompatible: If model A is incompatible to model B, model A is not
+#                guaranteed to run where model B runs and the other way around.
+#
+# @identical: If model A is identical to model B, model A is guaranteed to run
+#             where model B runs and the other way around.
+#
+# @superset: If model A is a superset of model B, model B is guaranteed to run
+#            where model A runs. There are no guarantees about the other way.
+#
+# @subset: If model A is a subset of model B, model A is guaranteed to run
+#          where model B runs. There are no guarantees about the other way.
+#
+# Since: 2.8.0
+##
+{ 'enum': 'CpuModelCompareResult',
+  'data': [ 'incompatible', 'identical', 'superset', 'subset' ] }
+
+##
+# @CpuModelCompareInfo
+#
+# The result of a CPU model comparison.
+#
+# @result: The result of the compare operation.
+# @responsible-properties: List of properties that led to the comparison result
+#                          not being identical.
+#
+# @responsible-properties is a list of QOM property names that led to
+# both CPUs not being detected as identical. For identical models, this
+# list is empty.
+# If a QOM property is read-only, that means there's no known way to make the
+# CPU models identical. If the special property name "type" is included, the
+# models are by definition not identical and cannot be made identical.
+#
+# Since: 2.8.0
+##
+{ 'struct': 'CpuModelCompareInfo',
+  'data': {'result': 'CpuModelCompareResult',
+           'responsible-properties': ['str']
+          }
+}
+
+##
+# @query-cpu-model-comparison:
+#
+# Compares two CPU models, returning how they compare in a specific
+# configuration. The results indicates how both models compare regarding
+# runnability. This result can be used by tooling to make decisions if a
+# certain CPU model will run in a certain configuration or if a compatible
+# CPU model has to be created by baselining.
+#
+# Usually, a CPU model is compared against the maximum possible CPU model
+# of a ceratin configuration (e.g. the "host" model for KVM). If that CPU
+# model is identical or a subset, it will run in that configuration.
+#
+# 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 comparing CPU models.
+#
+# Returns: a CpuModelBaselineInfo. Returns an error if comparing 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-comparison',
+  'data': { 'modela': 'CpuModelInfo', 'modelb': 'CpuModelInfo' },
+  'returns': 'CpuModelCompareInfo' }
+
 # @AddfdInfo:
 #
 # Information about a file descriptor that was added to an fd set.

qmp-commands.hx

@@ -3947,6 +3947,12 @@ EQMP
         .mhandler.cmd_new = qmp_marshal_query_cpu_model_expansion,
     },
 
+    {
+        .name       = "query-cpu-model-comparison",
+        .args_type  = "modela:q,modelb:q",
+        .mhandler.cmd_new = qmp_marshal_query_cpu_model_comparison,
+    },
+
     {
         .name       = "query-target",
         .args_type  = "",

qmp.c

@@ -614,6 +614,13 @@ CpuModelExpansionInfo *qmp_query_cpu_model_expansion(CpuModelExpansionType type,
     return arch_query_cpu_model_expansion(type, model, errp);
 }
 
+CpuModelCompareInfo *qmp_query_cpu_model_comparison(CpuModelInfo *modela,
+                                                    CpuModelInfo *modelb,
+                                                    Error **errp)
+{
+    return arch_query_cpu_model_comparison(modela, modelb, errp);
+}
+
 void qmp_add_client(const char *protocol, const char *fdname,
                     bool has_skipauth, bool skipauth, bool has_tls, bool tls,
                     Error **errp)

stubs/Makefile.objs

@@ -1,5 +1,6 @@
 stub-obj-y += arch-query-cpu-def.o
 stub-obj-y += arch-query-cpu-model-expansion.o
+stub-obj-y += arch-query-cpu-model-comparison.o
 stub-obj-y += bdrv-next-monitor-owned.o
 stub-obj-y += blk-commit-all.o
 stub-obj-y += blockdev-close-all-bdrv-states.o

stubs/arch-query-cpu-model-comparison.c

@@ -0,0 +1,12 @@
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+#include "sysemu/arch_init.h"
+#include "qapi/qmp/qerror.h"
+
+CpuModelCompareInfo *arch_query_cpu_model_comparison(CpuModelInfo *modela,
+                                                     CpuModelInfo *modelb,
+                                                     Error **errp)
+{
+    error_setg(errp, QERR_UNSUPPORTED);
+    return NULL;
+}