[Qemu-devel] [PATCH] VARIANT 1: reuse device compat logic to pick preffered CPU's migration instance_id

[Igor Mammedov <imammedo@redhat.com>]

this approach i I preffer as it uses less per machine migration glue
and follows typical compat pattern for devices

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
---
 exec.c              |  7 +++++--
 hw/i386/pc.c        | 10 +++++++---
 include/hw/compat.h |  6 +++++-
 include/qom/cpu.h   |  3 +++
 qom/cpu.c           | 13 +++++++++++++
 5 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/exec.c b/exec.c
index 0122ef7..79e1dcb 100644
--- a/exec.c
+++ b/exec.c
@@ -670,6 +670,7 @@ void cpu_exec_init(CPUState *cpu, Error **errp)
 {
     CPUClass *cc = CPU_GET_CLASS(cpu);
     Error *local_err = NULL;
+    int migration_id;
 
     cpu->as = NULL;
     cpu->num_ases = 0;
@@ -708,11 +709,13 @@ void cpu_exec_init(CPUState *cpu, Error **errp)
     (void) cc;
     cpu_list_unlock();
 #else
+    migration_id = cc->use_migration_id > 0 ?
+        cpu->migration_id : cpu->cpu_index;
     if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
-        vmstate_register(NULL, cpu->cpu_index, &vmstate_cpu_common, cpu);
+        vmstate_register(NULL, migration_id, &vmstate_cpu_common, cpu);
     }
     if (cc->vmsd != NULL) {
-        vmstate_register(NULL, cpu->cpu_index, cc->vmsd, cpu);
+        vmstate_register(NULL, migration_id, cc->vmsd, cpu);
     }
 #endif
 }
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index cd1745e..f041279 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1040,9 +1040,10 @@ void pc_acpi_smi_interrupt(void *opaque, int irq, int level)
 }
 
 static X86CPU *pc_new_cpu(const char *cpu_model, int64_t apic_id,
-                          Error **errp)
+                          Error **errp, int migration_id)
 {
     X86CPU *cpu = NULL;
+    CPUState *cs = CPU(cpu);
     Error *local_err = NULL;
 
     cpu = cpu_x86_create(cpu_model, &local_err);
@@ -1050,6 +1051,7 @@ static X86CPU *pc_new_cpu(const char *cpu_model, int64_t apic_id,
         goto out;
     }
 
+    cs->migration_id = migration_id;
     object_property_set_int(OBJECT(cpu), apic_id, "apic-id", &local_err);
     object_property_set_bool(OBJECT(cpu), true, "realized", &local_err);
 
@@ -1093,7 +1095,7 @@ void pc_hot_add_cpu(const int64_t id, Error **errp)
         return;
     }
 
-    cpu = pc_new_cpu(machine->cpu_model, apic_id, &local_err);
+    cpu = pc_new_cpu(machine->cpu_model, apic_id, &local_err, id);
     if (local_err) {
         error_propagate(errp, local_err);
         return;
@@ -1137,7 +1139,7 @@ void pc_cpus_init(PCMachineState *pcms)
         pcms->possible_cpus->len++;
         if (i < smp_cpus) {
             cpu = pc_new_cpu(machine->cpu_model, x86_cpu_apic_id_from_index(i),
-                             &error_fatal);
+                             &error_fatal, i);
             pcms->possible_cpus->cpus[i].cpu = CPU(cpu);
             object_unref(OBJECT(cpu));
         }
@@ -2012,7 +2014,9 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     PCMachineClass *pcmc = PC_MACHINE_CLASS(oc);
     HotplugHandlerClass *hc = HOTPLUG_HANDLER_CLASS(oc);
     NMIClass *nc = NMI_CLASS(oc);
+    CPUClass *cc = CPU_CLASS(object_class_by_name(TYPE_CPU));
 
+    cc->use_migration_id = true;
     pcmc->get_hotplug_handler = mc->get_hotplug_handler;
     pcmc->pci_enabled = true;
     pcmc->has_acpi_build = true;
diff --git a/include/hw/compat.h b/include/hw/compat.h
index 636befe..a66e80d 100644
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -2,7 +2,11 @@
 #define HW_COMPAT_H
 
 #define HW_COMPAT_2_6 \
-    /* empty */
+    { \
+        .driver   = TYPE_CPU, \
+        .property = "use-migration-id", \
+        .value    = "off", \
+    },
 
 #define HW_COMPAT_2_5 \
     {\
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 32f3af3..a29a2c9 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -177,6 +177,8 @@ typedef struct CPUClass {
                                 void *opaque);
 
     const struct VMStateDescription *vmsd;
+    int use_migration_id;
+
     int gdb_num_core_regs;
     const char *gdb_core_xml_file;
     gchar * (*gdb_arch_name)(CPUState *cpu);
@@ -360,6 +362,7 @@ struct CPUState {
        (absolute value) offset as small as possible.  This reduces code
        size, especially for hosts without large memory offsets.  */
     uint32_t tcg_exit_req;
+    int migration_id;
 };
 
 QTAILQ_HEAD(CPUTailQ, CPUState);
diff --git a/qom/cpu.c b/qom/cpu.c
index 751e992..3eb48b9 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -342,11 +342,24 @@ static int64_t cpu_common_get_arch_id(CPUState *cpu)
     return cpu->cpu_index;
 }
 
+static void cpu_common_set_use_migration_id(Object *obj, bool value,
+                                            Error **err)
+{
+    CPUClass *cc = CPU_GET_CLASS(obj);
+    cc->use_migration_id = value ? 1 : 0;
+}
+
 static void cpu_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     CPUClass *k = CPU_CLASS(klass);
 
+    k->use_migration_id = -1;
+    object_class_property_add_bool(klass, "use-migration-id",
+                                   NULL,
+                                   cpu_common_set_use_migration_id,
+                                   &error_abort);
+
     k->class_by_name = cpu_common_class_by_name;
     k->parse_features = cpu_common_parse_features;
     k->reset = cpu_common_reset;
-- 
1.8.3.1