QMP: Add query-hotpluggable-cpus

It will allow mgmt to query present and hotpluggable CPU objects,
it is required from a target platform that wishes to support command
to implement and set MachineClass.query_hotpluggable_cpus callback,
which will return a list of possible CPU objects with options that
would be needed for hotplugging possible CPU objects.

There are:
'type': 'str' - QOM CPU object type for usage with device_add
'vcpus-count': 'int' - number of logical VCPU threads per
                        CPU object (mgmt needs to know)

and a set of optional fields that are to used for hotplugging a CPU
objects and would allows mgmt tools to know what/where it could be
hotplugged;
[node],[socket],[core],[thread]

For present CPUs there is a 'qom-path' field which would allow mgmt to
inspect whatever object/abstraction the target platform considers
as CPU object.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

include/hw/boards.h

@@ -81,6 +81,10 @@ typedef struct {
  *    Returns an array of @CPUArchId architecture-dependent CPU IDs
  *    which includes CPU IDs for present and possible to hotplug CPUs.
  *    Caller is responsible for freeing returned list.
+ * @query_hotpluggable_cpus:
+ *    Returns a @HotpluggableCPUList, which describes CPUs objects which
+ *    could be added with -device/device_add.
+ *    Caller is responsible for freeing returned list.
  */
 struct MachineClass {
     /*< private >*/
@@ -124,6 +128,7 @@ struct MachineClass {
                                            DeviceState *dev);
     unsigned (*cpu_index_to_socket_id)(unsigned cpu_index);
     CPUArchIdList *(*possible_cpu_arch_ids)(MachineState *machine);
+    HotpluggableCPUList *(*query_hotpluggable_cpus)(MachineState *machine);
 };
 
 /**

monitor.c

@@ -4273,3 +4273,16 @@ GICCapabilityList *qmp_query_gic_capabilities(Error **errp)
     return NULL;
 }
 #endif
+
+HotpluggableCPUList *qmp_query_hotpluggable_cpus(Error **errp)
+{
+    MachineState *ms = MACHINE(qdev_get_machine());
+    MachineClass *mc = MACHINE_GET_CLASS(ms);
+
+    if (!mc->query_hotpluggable_cpus) {
+        error_setg(errp, QERR_FEATURE_DISABLED, "query-hotpluggable-cpus");
+        return NULL;
+    }
+
+    return mc->query_hotpluggable_cpus(ms);
+}

qapi-schema.json

@@ -4253,3 +4253,58 @@
 # Since: 2.6
 ##
 { 'command': 'query-gic-capabilities', 'returns': ['GICCapability'] }
+
+##
+# CpuInstanceProperties
+#
+# List of properties to be used for hotplugging a CPU instance,
+# it should be passed by management with device_add command when
+# a CPU is being hotplugged.
+#
+# Note: currently there are 4 properties that could be present
+# but management should be prepared to pass through other
+# properties with device_add command to allow for future
+# interface extension.
+#
+# @node: #optional NUMA node ID the CPU belongs to
+# @socket: #optional socket number within node/board the CPU belongs to
+# @core: #optional core number within socket the CPU belongs to
+# @thread: #optional thread number within core the CPU belongs to
+#
+# Since: 2.7
+##
+{ 'struct': 'CpuInstanceProperties',
+  'data': { '*node': 'int',
+            '*socket': 'int',
+            '*core': 'int',
+            '*thread': 'int'
+  }
+}
+
+##
+# @HotpluggableCPU
+#
+# @type: CPU object type for usage with device_add command
+# @props: list of properties to be used for hotplugging CPU
+# @vcpus-count: number of logical VCPU threads @HotpluggableCPU provides
+# @qom-path: #optional link to existing CPU object if CPU is present or
+#            omitted if CPU is not present.
+#
+# Since: 2.7
+##
+{ 'struct': 'HotpluggableCPU',
+  'data': { 'type': 'str',
+            'vcpus-count': 'int',
+            'props': 'CpuInstanceProperties',
+            '*qom-path': 'str'
+          }
+}
+
+##
+# @query-hotpluggable-cpus
+#
+# Returns: a list of HotpluggableCPU objects.
+#
+# Since: 2.7
+##
+{ 'command': 'query-hotpluggable-cpus', 'returns': ['HotpluggableCPU'] }

qmp-commands.hx

@@ -4960,3 +4960,26 @@ Example:
                 { "version": 3, "emulated": false, "kernel": true } ] }
 
 EQMP
+
+    {
+        .name       = "query-hotpluggable-cpus",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_query_hotpluggable_cpus,
+    },
+
+SQMP
+Show existing/possible CPUs
+---------------------------
+
+Arguments: None.
+
+Example for pseries machine type started with
+-smp 2,cores=2,maxcpus=4 -cpu POWER8:
+
+-> { "execute": "query-hotpluggable-cpus" }
+<- {"return": [
+     { "props": { "core": 8 }, "type": "POWER8-spapr-cpu-core",
+       "vcpus-count": 1 },
+     { "props": { "core": 0 }, "type": "POWER8-spapr-cpu-core",
+       "vcpus-count": 1, "qom-path": "/machine/unattached/device[0]"}
+   ]}'