qemu_vm: Fix swtpm path too long for vTPM + ping-pong migration

The current workaround is adding "_copied" string into the swtpm path
for vTPM migration. When we do ping-pong migration few times, the socket
path is longer than system limitation(107), which raises "Path for
UnioIO socket is too long". But actually the even times' migration can
use the source vTPM socket, so here add an action to roll back the tpm.

Signed-off-by: Yihuang Yu <[email protected]>

virttest/qemu_vm.py

@@ -4463,21 +4463,27 @@ def _set_migrate_capability(vm, capability, value, is_src_vm=True):
             swtpm_dir = os.path.join(data_dir.get_data_dir(), "swtpm")
             tpms = clone.params.objects("tpms")
             tpms_copy = []
-            for tpm in tpms:
-                tpm_name = "%s_%s" % (self.name, tpm)
-                tpm_path = os.path.join(swtpm_dir, '%s_state' % tpm_name)
-                tpm_copied_path = os.path.join(swtpm_dir, '%s_copied_state' %
-                                               tpm_name)
-                if os.path.exists(tpm_copied_path):
-                    shutil.rmtree(tpm_copied_path)
-                shutil.copytree(tpm_path, tpm_copied_path)
-                tpms_copy.append(tpm + "_copied")
-                for param in clone.params.copy():
-                    if param.endswith("_" + tpm):
-                        clone.params[param + "_copied"] = clone.params[param]
-                        del clone.params[param]
-                clone.params["tpm_overwrite_%s_copied" % tpm] = "no"
-            clone.params["tpms"] = " ".join(tpms_copy)
+            _rollback_tpms = clone.params.get("_rollback_tpms")
+
+            if _rollback_tpms:
+                clone.params["tpms"] = clone.params.pop("_rollback_tpms")
+            else:
+                # Backup vTPM resources for ping-pong migration
+                clone.params["_rollback_tpms"] = clone.params["tpms"]
+                for tpm in tpms:
+                    tpm_name = "%s_%s" % (self.name, tpm)
+                    tpm_path = os.path.join(swtpm_dir, '%s_state' % tpm_name)
+                    tpm_copied_path = os.path.join(swtpm_dir, '%s_copied_state' %
+                                                   tpm_name)
+                    if os.path.exists(tpm_copied_path):
+                        shutil.rmtree(tpm_copied_path)
+                    shutil.copytree(tpm_path, tpm_copied_path)
+                    tpms_copy.append(tpm + "_copied")
+                    for param in clone.params.copy():
+                        if param.endswith("_" + tpm):
+                            clone.params[param + "_copied"] = clone.params[param]
+                    clone.params["tpm_overwrite_%s_copied" % tpm] = "no"
+                clone.params["tpms"] = " ".join(tpms_copy)
 
         try:
             if (local and not (migration_exec_cmd_src and