feat(revpiconfig): Add CmdLineTxt class for managing cmdline.txt

Introduced the `CmdLineTxt` class to handle parsing, modifying, and
writing operations on the `cmdline.txt` file with thread safety.
Implemented methods for setting, removing keys, and ensuring safe file
operations.

Signed-off-by: Sven Sager <s.sager@kunbus.com>

src/revpi_middleware/dbus_middleware1/system_config/revpi_config.py

@@ -10,6 +10,7 @@ from glob import glob
 from logging import getLogger
 from os import X_OK, access
 from os.path import exists, join
+from threading import Lock
 from typing import List, Optional
 
 from pydbus import SystemBus
@@ -24,6 +25,8 @@ ConfigVariable = namedtuple("ConfigVariable", ["name", "value", "line_index"])
 LINUX_BT_CLASS_PATH = "/sys/class/bluetooth"
 LINUX_WLAN_CLASS_PATH = "/sys/class/ieee80211"
 CONFIG_TXT_LOCATIONS = ("/boot/firmware/config.txt", "/boot/config.txt")
+CMDLINE_TXT_LOCK = Lock()
+CONFIG_TXT_LOCK = Lock()
 
 
 class ComputeModuleTypes(IntEnum):
@@ -219,6 +222,61 @@ class RevPiConfig:
         return bool(self._wlan_class_path)
 
 
+class CmdLineTxt:
+
+    # Value is optional, "?:=" non-capturing the "="
+    re_name_value = re.compile(r"(?P<key>[^\s=]+)(?:=(?P<value>\S+))?")
+
+    def __init__(self):
+        self._cmdline_txt_path = ""
+        for path in CONFIG_TXT_LOCATIONS:
+            if exists(path):
+                self._cmdline_txt_path = path
+                break
+
+        if not self._cmdline_txt_path:
+            raise FileNotFoundError("no config.txt found")
+
+    def _get_cmdline_dict(self) -> dict:
+        with CMDLINE_TXT_LOCK:
+            with open(self._cmdline_txt_path, "r") as file:
+                cmdline = file.read()
+
+        return {
+            match.group("key"): match.group("value")
+            for match in self.re_name_value.finditer(cmdline)
+        }
+
+    def _write_cmdline_dict(self, cmdline_dict: dict) -> None:
+        with CMDLINE_TXT_LOCK:
+
+            tmp_path = f"{self._cmdline_txt_path}.tmp"
+            with open(tmp_path, "w") as file:
+                str_cmdline = ""
+                for key, value in cmdline_dict.items():
+                    if value is None:
+                        str_cmdline += f"{key} "
+                    else:
+                        str_cmdline += f"{key}={value} "
+
+                str_cmdline = str_cmdline.strip()
+                file.write(str_cmdline + "\n")
+
+            shutil.move(tmp_path, self._cmdline_txt_path)
+
+    def remove_key(self, key: str) -> None:
+        dc_cmdline = self._get_cmdline_dict()
+        if key in dc_cmdline:
+            del dc_cmdline[key]
+            self._write_cmdline_dict(dc_cmdline)
+
+    def set_key_value(self, key: str, value: Optional[str] = None) -> None:
+        dc_cmdline = self._get_cmdline_dict()
+        if key not in dc_cmdline or dc_cmdline.get(key, value) != value:
+            dc_cmdline[key] = value
+            self._write_cmdline_dict(dc_cmdline)
+
+
 class ConfigTxt:
     """
     Configuration file handler for managing 'config.txt'.
@@ -228,11 +286,6 @@ class ConfigTxt:
     to manipulate specific parameters within the configuration and supports
     managing dtoverlay and dtparam entries. The primary aim of this class
     is to abstract file operations and make modifications user-friendly.
-
-    Attributes:
-        _config_txt_path (str): The path to the configuration file `config.txt`.
-        _config_txt_lines (list[str]): Contains all lines of the configuration
-            file as a list of strings, where each string represents a line.
     """
 
     re_name_value = re.compile(r"^\s*(?!#)(?P<name>[^=\s].+?)\s*=\s*(?P<value>\S+)\s*$")
@@ -318,8 +371,9 @@ class ConfigTxt:
         Returns:
             None
         """
-        with open(self._config_txt_path, "r") as f:
+        with CONFIG_TXT_LOCK:
-            self._config_txt_lines = f.readlines()
+            with open(self._config_txt_path, "r") as f:
+                self._config_txt_lines = f.readlines()
 
     def save_config(self):
         """
@@ -333,10 +387,11 @@ class ConfigTxt:
         if not self._config_txt_lines:
             return
 
-        tmp_path = f"{self._config_txt_path}.tmp"
+        with CONFIG_TXT_LOCK:
-        with open(tmp_path, "w") as f:
+            tmp_path = f"{self._config_txt_path}.tmp"
-            f.writelines(self._config_txt_lines)
+            with open(tmp_path, "w") as f:
-        shutil.move(tmp_path, self._config_txt_path)
+                f.writelines(self._config_txt_lines)
+            shutil.move(tmp_path, self._config_txt_path)
 
         self._config_txt_lines.clear()