From: Juraj Marcin <jmarcin@redhat.com>

This allows devices to specify when during migration their fields should
be saved. For now there are two Save Phases defined.

EARLY_START

These devices are saved during qemu_savevm_state_setup(), and
corresponds to migration SETUP state, same behavior as the former
early_setup flag.

COMPLETE

These devices are saved during migration completion or switch-over with
qemu_savevm_state_complete_precopy_non_iterable(), this corresponds to
the migration DEVICE state. This is the default phase if none is
specified explicitly.

This also allows introduction of other phases in the future, for example
ITERATE_LIVE and POSTCOPY once support for iterative devices and
postcopy is implemented in VMSD, and for the NETPASS phase implemented
in this series.

Signed-off-by: Juraj Marcin <jmarcin@redhat.com>
---
 hw/virtio/virtio-mem.c      |  2 +-
 include/migration/vmstate.h | 27 +++++++++++++++++++--------
 migration/savevm.c          |  4 ++--
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index c1e2defb68..6d3e3746e5 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -1438,7 +1438,7 @@ static const VMStateDescription vmstate_virtio_mem_device_early = {
     .name = "virtio-mem-device-early",
     .minimum_version_id = 1,
     .version_id = 1,
-    .early_setup = true,
+    .phase = VMS_PHASE_EARLY_SETUP,
     .post_load = virtio_mem_post_load_early,
     .fields = (const VMStateField[]) {
         VMSTATE_WITH_TMP(VirtIOMEM, VirtIOMEMMigSanityChecks,
diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index ed9095a466..62d7e9fe38 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -186,18 +186,29 @@ struct VMStateField {
     bool (*field_exists)(void *opaque, int version_id);
 };
 
-struct VMStateDescription {
-    const char *name;
-    bool unmigratable;
+typedef enum {
     /*
-     * This VMSD describes something that should be sent during setup phase
-     * of migration. It plays similar role as save_setup() for explicitly
+     * Specifies a VMSD of a device that should be migrated during the migration
+     * completion phase (switch-over). (Default behavior, same behavior as
+     * before the introduction of save phase.)
+     */
+    VMS_PHASE_COMPLETE = 0,
+    /*
+     * Specifies a VMSD of a device that should be saved during setup phase of
+     * migration. It plays similar role as save_setup() for explicitly
      * registered vmstate entries, so it can be seen as a way to describe
      * save_setup() in VMSD structures.
-     *
+     */
+    VMS_PHASE_EARLY_SETUP,
+} VMStateSavePhase;
+
+struct VMStateDescription {
+    const char *name;
+    bool unmigratable;
+    /*
      * Note that for now, a SaveStateEntry cannot have a VMSD and
      * operations (e.g., save_setup()) set at the same time. Consequently,
-     * save_setup() and a VMSD with early_setup set to true are mutually
+     * save_setup() and a VMSD with phase set to EARLY_SETUP are mutually
      * exclusive. For this reason, also early_setup VMSDs are migrated in a
      * QEMU_VM_SECTION_FULL section, while save_setup() data is migrated in
      * a QEMU_VM_SECTION_START section.
@@ -213,7 +224,7 @@ struct VMStateDescription {
      *          <0 on error where -value is an error number from errno.h
      */
 
-    bool early_setup;
+    VMStateSavePhase phase;
     int version_id;
     int minimum_version_id;
     MigrationPriority priority;
diff --git a/migration/savevm.c b/migration/savevm.c
index 1020094fc8..78eb1d6165 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1370,7 +1370,7 @@ int qemu_savevm_state_setup(QEMUFile *f, Error **errp)
 
     trace_savevm_state_setup();
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
-        if (se->vmsd && se->vmsd->early_setup) {
+        if (se->vmsd && se->vmsd->phase == VMS_PHASE_EARLY_SETUP) {
             ret = vmstate_save(f, se, vmdesc, errp);
             if (ret) {
                 migrate_error_propagate(ms, error_copy(*errp));
@@ -1672,7 +1672,7 @@ int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
     cpu_synchronize_all_states();
 
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
-        if (se->vmsd && se->vmsd->early_setup) {
+        if (se->vmsd && se->vmsd->phase != VMS_PHASE_COMPLETE) {
             /* Already saved during qemu_savevm_state_setup(). */
             continue;
         }
-- 
2.52.0