T7352: add util for enabling vyconf backend for smoketests

2 files changed, 90 insertions, 2 deletions

diff --git a/python/vyos/configsession.py b/python/vyos/configsession.py
index a070736cd..8131e0ea3 100644
--- a/python/vyos/configsession.py
+++ b/python/vyos/configsession.py
@@ -22,9 +22,9 @@ from vyos.defaults import directories
 from vyos.utils.process import is_systemd_service_running
 from vyos.utils.dict import dict_to_paths
 from vyos.utils.boot import boot_configuration_complete
+from vyos.utils.backend import vyconf_backend
 from vyos.vyconf_session import VyconfSession
 
-vyconf_backend = False
 
 CLI_SHELL_API = '/bin/cli-shell-api'
 SET = '/opt/vyatta/sbin/my_set'
@@ -173,7 +173,7 @@ class ConfigSession(object):
 
         self.__run_command([CLI_SHELL_API, 'setupSession'])
 
-        if vyconf_backend and boot_configuration_complete():
+        if vyconf_backend() and boot_configuration_complete():
             self._vyconf_session = VyconfSession(on_error=ConfigSessionError)
         else:
             self._vyconf_session = None
diff --git a/python/vyos/utils/backend.py b/python/vyos/utils/backend.py
new file mode 100644
index 000000000..400ea9b69
--- /dev/null
+++ b/python/vyos/utils/backend.py
@@ -0,0 +1,88 @@
+# Copyright 2025 VyOS maintainers and contributors <maintainers@vyos.io>
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this library.  If not, see <http://www.gnu.org/licenses/>.
+
+# N.B. the following is a temporary addition for running smoketests under
+# vyconf and is not to be called explicitly, at the risk of catastophe.
+
+# pylint: disable=wrong-import-position
+
+from pathlib import Path
+
+from vyos.utils.io import ask_yes_no
+from vyos.utils.process import call
+
+VYCONF_SENTINEL = '/run/vyconf_backend'
+
+MSG_ENABLE_VYCONF = 'This will enable the vyconf backend for testing. Proceed?'
+MSG_DISABLE_VYCONF = (
+    'This will restore the legacy backend; it requires a reboot. Proceed?'
+)
+
+# read/set immutable file attribute without popen:
+# https://www.geeklab.info/2021/04/chattr-and-lsattr-in-python/
+import fcntl  # pylint: disable=C0411 # noqa: E402
+from array import array  # pylint: disable=C0411 # noqa: E402
+
+# FS constants - see /uapi/linux/fs.h in kernel source
+# or <elixir.free-electrons.com/linux/latest/source/include/uapi/linux/fs.h>
+FS_IOC_GETFLAGS = 0x80086601
+FS_IOC_SETFLAGS = 0x40086602
+FS_IMMUTABLE_FL = 0x010
+
+
+def chattri(filename: str, value: bool):
+    with open(filename, 'r') as f:
+        arg = array('L', [0])
+        fcntl.ioctl(f.fileno(), FS_IOC_GETFLAGS, arg, True)
+        if value:
+            arg[0] = arg[0] | FS_IMMUTABLE_FL
+        else:
+            arg[0] = arg[0] & ~FS_IMMUTABLE_FL
+        fcntl.ioctl(f.fileno(), FS_IOC_SETFLAGS, arg, True)
+
+
+def lsattri(filename: str) -> bool:
+    with open(filename, 'r') as f:
+        arg = array('L', [0])
+        fcntl.ioctl(f.fileno(), FS_IOC_GETFLAGS, arg, True)
+    return bool(arg[0] & FS_IMMUTABLE_FL)
+
+
+# End: read/set immutable file attribute without popen
+
+
+def vyconf_backend() -> bool:
+    return Path(VYCONF_SENTINEL).exists() and lsattri(VYCONF_SENTINEL)
+
+
+def set_vyconf_backend(value: bool, no_prompt: bool = False):
+    vyconfd_service = 'vyconfd.service'
+    match value:
+        case True:
+            if vyconf_backend():
+                return
+            if not no_prompt and not ask_yes_no(MSG_ENABLE_VYCONF):
+                return
+            Path(VYCONF_SENTINEL).touch()
+            chattri(VYCONF_SENTINEL, True)
+            call(f'systemctl restart {vyconfd_service}')
+        case False:
+            if not vyconf_backend():
+                return
+            if not no_prompt and not ask_yes_no(MSG_DISABLE_VYCONF):
+                return
+            chattri(VYCONF_SENTINEL, False)
+            Path(VYCONF_SENTINEL).unlink()
+            call('/sbin/shutdown -r now')