migration: Add the configuration vmstate to the json writer

Make the migration json writer part of MigrationState struct, allowing
the 'configuration' object be serialized to json.

This will facilitate the parsing of the 'configuration' object in the
next patch that fixes analyze-migration.py for arm.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231009184326.15777-2-farosas@suse.de>

migration/migration.c

@@ -1442,6 +1442,7 @@ int migrate_init(MigrationState *s, Error **errp)
     error_free(s->error);
     s->error = NULL;
     s->hostname = NULL;
+    s->vmdesc = NULL;
 
     migrate_set_state(&s->state, MIGRATION_STATUS_NONE, MIGRATION_STATUS_SETUP);
 

migration/savevm.c

@@ -1217,13 +1217,27 @@ void qemu_savevm_non_migratable_list(strList **reasons)
 
 void qemu_savevm_state_header(QEMUFile *f)
 {
+    MigrationState *s = migrate_get_current();
+
+    s->vmdesc = json_writer_new(false);
+
     trace_savevm_state_header();
     qemu_put_be32(f, QEMU_VM_FILE_MAGIC);
     qemu_put_be32(f, QEMU_VM_FILE_VERSION);
 
-    if (migrate_get_current()->send_configuration) {
+    if (s->send_configuration) {
         qemu_put_byte(f, QEMU_VM_CONFIGURATION);
-        vmstate_save_state(f, &vmstate_configuration, &savevm_state, 0);
+
+        /*
+         * This starts the main json object and is paired with the
+         * json_writer_end_object in
+         * qemu_savevm_state_complete_precopy_non_iterable
+         */
+        json_writer_start_object(s->vmdesc, NULL);
+
+        json_writer_start_object(s->vmdesc, "configuration");
+        vmstate_save_state(f, &vmstate_configuration, &savevm_state, s->vmdesc);
+        json_writer_end_object(s->vmdesc);
     }
 }
 
@@ -1272,8 +1286,6 @@ void qemu_savevm_state_setup(QEMUFile *f)
     Error *local_err = NULL;
     int ret;
 
-    ms->vmdesc = json_writer_new(false);
-    json_writer_start_object(ms->vmdesc, NULL);
     json_writer_int64(ms->vmdesc, "page_size", qemu_target_page_size());
     json_writer_start_array(ms->vmdesc, "devices");