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>

include/sysemu/arch_init.h

@@ -41,5 +41,8 @@ CpuModelExpansionInfo *arch_query_cpu_model_expansion(CpuModelExpansionType type
 CpuModelCompareInfo *arch_query_cpu_model_comparison(CpuModelInfo *modela,
                                                      CpuModelInfo *modelb,
                                                      Error **errp);
+CpuModelBaselineInfo *arch_query_cpu_model_baseline(CpuModelInfo *modela,
+                                                    CpuModelInfo *modelb,
+                                                    Error **errp);
 
 #endif

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.

qmp-commands.hx

@@ -3953,6 +3953,12 @@ EQMP
         .mhandler.cmd_new = qmp_marshal_query_cpu_model_comparison,
     },
 
+    {
+        .name       = "query-cpu-model-baseline",
+        .args_type  = "modela:q,modelb:q",
+        .mhandler.cmd_new = qmp_marshal_query_cpu_model_baseline,
+    },
+
     {
         .name       = "query-target",
         .args_type  = "",

qmp.c

@@ -621,6 +621,13 @@ CpuModelCompareInfo *qmp_query_cpu_model_comparison(CpuModelInfo *modela,
     return arch_query_cpu_model_comparison(modela, modelb, errp);
 }
 
+CpuModelBaselineInfo *qmp_query_cpu_model_baseline(CpuModelInfo *modela,
+                                                   CpuModelInfo *modelb,
+                                                   Error **errp)
+{
+    return arch_query_cpu_model_baseline(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

@@ -1,6 +1,7 @@
 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 += arch-query-cpu-model-baseline.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-baseline.c

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