fix(logs): libvirt prints no errors on the processes' stderr

libvirt's default handler printed each error on stderr without saying
where it came from: in Docker those lines went to docker logs, and a
VM page read of a shut-off VM left one there. Every process that talks to
libvirt imports vrtManager.connection, which now registers a silent
handler; the errors still reach their callers as exceptions. The
console callback's own registration is dropped.

conf/daemon/consolecallback

@@ -28,9 +28,6 @@ from instances.utils import can_open_console  # noqa: E402
 from operations.utils import public_error_text  # noqa: E402
 from vrtManager.connection import connection_manager  # noqa: E402
 
-# libvirt prints its errors on stderr, which is the user's terminal: they are
-# raised and told in one line instead
-libvirt.registerErrorHandler(lambda context, error: None, None)
 SEND_WAIT = 5  # seconds a paste may wait for the VM to take it
 ACCESS_CHECK = 10  # seconds between checks that the user may still use the console
 

vrtManager/connection.py

@@ -58,6 +58,10 @@ CLOSE_REASONS = {
 SSH_COMMAND = os.path.join(os.path.dirname(os.path.abspath(__file__)), "libvirt-ssh")
 
 logger = logging.getLogger(__name__)
+# libvirt prints each error on stderr without saying where it came from; every
+# process that talks to libvirt imports this module. The errors are raised to
+# the callers, which handle or report them.
+libvirt.registerErrorHandler(lambda context, error: None, None)
 
 
 class wvmEventLoop(threading.Thread):

vrtManager/tests/test_connection.py

@@ -3,6 +3,8 @@
 import contextlib
 import os
 import socket
+import subprocess
+import sys
 import threading
 import time
 import unittest
@@ -410,3 +412,14 @@ class EventLoopTestCase(unittest.TestCase):
 
 if __name__ == "__main__":
     unittest.main()
+
+
+class LibvirtStderrTestCase(unittest.TestCase):
+    def test_a_libvirt_error_is_not_printed_on_stderr(self):
+        script = (
+            "from django.conf import settings; settings.configure(); "
+            "import libvirt, vrtManager.connection\n"
+            "try:\n    libvirt.open('test:///default').lookupByName('no-such-vm')\nexcept libvirt.libvirtError:\n    pass"
+        )
+        result = subprocess.run([sys.executable, "-c", script], cwd=os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))), capture_output=True, text=True)
+        self.assertEqual((result.returncode, result.stderr), (0, ""))