utils: T8541: add write-config-file-value helper

Introduce src/helpers/write-config-file-value.py to patch a saved config.boot
from scripts by writing a quoted CLI path with an optional value (omit --value
to create a valueless node).

Extend vyos.utils.config.write_saved_value() to safely update saved configs:
create missing parent nodes before tagging (ConfigTree.set_tag requires nodes
to exist) and then write the requested value/valueless leaf back to disk.

Remove the legacy serial console activation script which is now replaced by the
helper-based approach. The helper is run once during ISO Image assembly and will
inject the approprate serial console defintiions into config.boot.default.

1 files changed, 29 insertions, 0 deletions

diff --git a/python/vyos/utils/config.py b/python/vyos/utils/config.py
index 1f067e91e..5bba69a61 100644
--- a/python/vyos/utils/config.py
+++ b/python/vyos/utils/config.py
@@ -44,6 +44,35 @@ def read_saved_value(path: list):
         return ' '.join(res)
     return res
 
+def write_saved_value(path: list, value=None, config_path: str=config_file):
+    """Write or replace a node in a saved configuration.
+
+    - If value is None, the node is treated as valueless.
+    - Tag nodes in the path are detected via XML reference tree and marked on
+      the ConfigTree prior to setting the node.
+    """
+    if not isinstance(path, list) or not path:
+        raise ValueError('path must be a non-empty list')
+
+    from vyos.configtree import ConfigTree
+    from vyos.utils.file import read_file
+    from vyos.utils.file import write_file
+
+    config_string = read_file(config_path)
+    ct = ConfigTree(config_string)
+
+    # ConfigTree.set_tag() requires the node to exist.
+    # Create missing nodes along the path so tag marking works even when
+    # writing a completely new subtree into config.boot.
+    for target in flag(path):
+        if not ct.exists(target):
+            ct.create_node(target)
+
+    set_tags(ct, path)
+
+    ct.set(path, value=value, replace=True)
+    write_file(config_path, ct.to_string())
+
 def flag(l: list) -> list:
     res = [l[0:i] for i,_ in enumerate(l, start=1)]
     return res