[PATCH i-g-t 03/10] tools/vmtb: Fix VM snapshot query handling

[Adam Miszczak <adam.miszczak@linux.intel.com>]

QMP command 'query-named-block-nodes' is used to select a block device
for saving VM snapshot (QMP 'snapshot-save').

Add polling for the command's return message in QMP response queue.
It sporadically happened that unsolicited QMP message like:
[QMP RSP] <- {"timestamp": {...}, "event": "RTC_CHANGE" ...}
was falsely taken as a response to previously submitted
QMP 'query-named-block-nodes' command.
Hence, no 'block device node' argument is passed to
'snapshot-load' command which leads to migration tests fail.
Also, add a condition to check if a given block node
is writable (not read-only).

Signed-off-by: Adam Miszczak <adam.miszczak@linux.intel.com>
---
 .../machines/virtual/backends/qmp_monitor.py  | 25 ++++++++++---------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/tools/vmtb/bench/machines/virtual/backends/qmp_monitor.py b/tools/vmtb/bench/machines/virtual/backends/qmp_monitor.py
index ef3c8aa1c..d364a5711 100644
--- a/tools/vmtb/bench/machines/virtual/backends/qmp_monitor.py
+++ b/tools/vmtb/bench/machines/virtual/backends/qmp_monitor.py
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: MIT
-# Copyright © 2024 Intel Corporation
+# Copyright © 2024-2026 Intel Corporation
 
 import json
 import logging
@@ -123,17 +123,18 @@ class QmpMonitor():
         ret: typing.Dict = {}
 
         qmp_msg = self.qmp_queue.get()
-        # logger.debug('[QMP RSP Queue] -> %s', qmp_msg)
-        if 'return' in qmp_msg:
-            ret = qmp_msg.get('return')
-            for block in ret:
-                if block.get('drv') == 'qcow2':
-                    node_name = block.get('node-name')
-                    # Get the most recent state snapshot from the snapshots list:
-                    snapshots = block.get('image').get('snapshots')
-                    if snapshots:
-                        snapshot_tag = snapshots[-1].get('name')
-                    break
+        while 'return' not in qmp_msg:
+            qmp_msg = self.qmp_queue.get()
+
+        ret = qmp_msg.get('return')
+        for block in ret:
+            if block.get('drv') == 'qcow2' and block.get('ro') is False:
+                node_name = block.get('node-name')
+                # Get the most recent state snapshot from the snapshots list:
+                snapshots = block.get('image').get('snapshots')
+                if snapshots:
+                    snapshot_tag = snapshots[-1].get('name')
+                break
 
         return (node_name, snapshot_tag)
 
-- 
2.39.1