util: T1797: Optimized sysctl helpers

- modified `sysctl_read()` to return the whole value
- modified `sysctl_write()` logic to return `True` only in case a value was
changed successfully
- added `sysctl_apply()` to apply a dictionary of values at once

python/vyos/utils/system.py

@@ -0,0 +1,82 @@
+# Copyright 2023 VyOS maintainers and contributors <[email protected]>
+#
+# 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/>.
+
+from subprocess import run
+
+
+def sysctl_read(name: str) -> str:
+    """Read and return current value of sysctl() option
+
+    Args:
+        name (str): sysctl key name
+
+    Returns:
+        str: sysctl key value
+    """
+    tmp = run(['sysctl', '-nb', name], capture_output=True)
+    return tmp.stdout.decode()
+
+
+def sysctl_write(name: str, value: str | int) -> bool:
+    """Change value via sysctl()
+
+    Args:
+        name (str): sysctl key name
+        value (str | int): sysctl key value
+
+    Returns:
+        bool: True if changed, False otherwise
+    """
+    # convert other types to string before comparison
+    if not isinstance(value, str):
+        value = str(value)
+    # do not change anything if a value is already configured
+    if sysctl_read(name) == value:
+        return True
+    # return False if sysctl call failed
+    if run(['sysctl', '-wq', f'{name}={value}']).returncode != 0:
+        return False
+    # compare old and new values
+    # sysctl may apply value, but its actual value will be
+    # different from requested
+    if sysctl_read(name) == value:
+        return True
+    # False in other cases
+    return False
+
+
+def sysctl_apply(sysctl_dict: dict[str, str], revert: bool = True) -> bool:
+    """Apply sysctl values.
+
+    Args:
+        sysctl_dict (dict[str, str]): dictionary with sysctl keys with values
+        revert (bool, optional): Revert to original values if new were not 
+        applied. Defaults to True.
+
+    Returns:
+        bool: True if all params configured properly, False in other cases
+    """
+    # get current values
+    sysctl_original: dict[str, str] = {}
+    for key_name in sysctl_dict.keys():
+        sysctl_original[key_name] = sysctl_read(key_name)
+    # apply new values and revert in case one of them was not applied
+    for key_name, value in sysctl_dict.items():
+        if not sysctl_write(key_name, value):
+            if revert:
+                sysctl_apply(sysctl_original, revert=False)
+            return False
+    # everything applied
+    return True