[Qemu-devel] [RFC PATCH v1 2/5] cpu: Introduce CPUState::migration_id

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

Add CPUState::migration_id and use that as instance_id in
vmstate_register() call.

Introduce use-migration-id property that allows target machines to
optionally switch to using migration_id instead of cpu_index.
This will help allow successful migration in cases where holes are
introduced in cpu_index range after CPU hot removals.

The default implementation of CPUClass:get_migration_id() continues
to return cpu_index.

Suggested-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
---
 exec.c            |  5 +++--
 include/qom/cpu.h |  6 ++++++
 qom/cpu.c         | 21 +++++++++++++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/exec.c b/exec.c
index fb73910..a8afeda 100644
--- a/exec.c
+++ b/exec.c
@@ -619,12 +619,13 @@ static void cpu_release_index(CPUState *cpu)
 void cpu_vmstate_register(CPUState *cpu)
 {
     CPUClass *cc = CPU_GET_CLASS(cpu);
+    int instance_id = cc->get_migration_id(cpu);
 
     if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
-        vmstate_register(NULL, cpu->cpu_index, &vmstate_cpu_common, cpu);
+        vmstate_register(NULL, instance_id, &vmstate_cpu_common, cpu);
     }
     if (cc->vmsd != NULL) {
-        vmstate_register(NULL, cpu->cpu_index, cc->vmsd, cpu);
+        vmstate_register(NULL, instance_id, cc->vmsd, cpu);
     }
 }
 
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 29ccf5c..6d00143 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -187,6 +187,7 @@ typedef struct CPUClass {
     bool (*cpu_exec_interrupt)(CPUState *cpu, int interrupt_request);
 
     void (*disas_set_info)(CPUState *cpu, disassemble_info *info);
+    int (*get_migration_id)(CPUState *cpu);
 } CPUClass;
 
 #ifdef HOST_WORDS_BIGENDIAN
@@ -273,6 +274,9 @@ struct qemu_work_item {
  * @kvm_fd: vCPU file descriptor for KVM.
  * @work_mutex: Lock to prevent multiple access to queued_work_*.
  * @queued_work_first: First asynchronous work pending.
+ * @migration_id: Use as instance_id argument in cpu vmstate_register calls
+ * @use_migration_id: Set to enforce the use of CPUClass.get_migration_id()
+ *     over cpu_index during vmstate registration.
  *
  * State of one CPU core or thread.
  */
@@ -360,6 +364,8 @@ 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;
+    bool use_migration_id;
 };
 
 QTAILQ_HEAD(CPUTailQ, CPUState);
diff --git a/qom/cpu.c b/qom/cpu.c
index 488ecc6..01cf136 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -326,6 +326,17 @@ static void cpu_common_realizefn(DeviceState *dev, Error **errp)
     }
 }
 
+static bool cpu_common_get_use_migration_id(Object *obj, Error **errp)
+{
+    return CPU(obj)->use_migration_id;
+}
+
+static void cpu_common_set_use_migration_id(Object *obj, bool value,
+                                            Error **err)
+{
+    CPU(obj)->use_migration_id = value;
+}
+
 static void cpu_common_initfn(Object *obj)
 {
     CPUState *cpu = CPU(obj);
@@ -336,6 +347,10 @@ static void cpu_common_initfn(Object *obj)
     qemu_mutex_init(&cpu->work_mutex);
     QTAILQ_INIT(&cpu->breakpoints);
     QTAILQ_INIT(&cpu->watchpoints);
+
+    object_property_add_bool(obj, "use-migration-id",
+                             cpu_common_get_use_migration_id,
+                             cpu_common_set_use_migration_id, NULL);
 }
 
 static void cpu_common_finalize(Object *obj)
@@ -348,6 +363,11 @@ static int64_t cpu_common_get_arch_id(CPUState *cpu)
     return cpu->cpu_index;
 }
 
+static int cpu_common_get_migration_id(CPUState *cpu)
+{
+    return cpu->cpu_index;
+}
+
 static void cpu_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -372,6 +392,7 @@ static void cpu_class_init(ObjectClass *klass, void *data)
     k->cpu_exec_enter = cpu_common_noop;
     k->cpu_exec_exit = cpu_common_noop;
     k->cpu_exec_interrupt = cpu_common_exec_interrupt;
+    k->get_migration_id = cpu_common_get_migration_id;
     dc->realize = cpu_common_realizefn;
     dc->unrealize = cpu_common_unrealizefn;
     /*
-- 
2.7.4