linux: kmsg plugin: improve return types

volatility3/framework/plugins/linux/kmsg.py

@@ -5,7 +5,7 @@ import re
 import logging
 from abc import ABC, abstractmethod
 from enum import Enum
-from typing import Generator, Iterator, List, Tuple
+from typing import Generator, Iterator, List, Tuple, Union
 
 from volatility3.framework import (
     class_subclasses,
@@ -135,10 +135,11 @@ class ABCKmsg(ABC):
             bool: True if the kernel being analyzed fulfill the class requirements.
         """
 
-    def get_string(self, addr: int, length: int) -> str:
+    def get_string(self, addr: int, length: int) -> Union[str, None]:
         layer = self._context.layers[self.layer_name]
         if not layer.is_valid(addr, length):
-            return ""
+            vollog.error("Failed to read log record at address 0x%x", addr)
+            return None
 
         txt = layer.read(addr, length)
 
@@ -268,7 +269,7 @@ class Kmsg_3_5_to_3_11(ABCKmsg):
     def _get_log_struct_name(self):
         return "log"
 
-    def get_text_from_log(self, msg) -> str:
+    def get_text_from_log(self, msg) -> Union[str, None]:
         log_struct_name = self._get_log_struct_name()
         log_struct_size = self.vmlinux.get_type(log_struct_name).size
         msg_offset = msg.vol.offset + log_struct_size
@@ -277,7 +278,8 @@ class Kmsg_3_5_to_3_11(ABCKmsg):
     def get_log_lines(self, msg) -> Generator[str, None, None]:
         if msg.text_len > 0:
             text = self.get_text_from_log(msg)
-            yield from text.splitlines()
+            if text:
+                yield from text.splitlines()
 
     def get_dict_lines(self, msg) -> Generator[str, None, None]:
         if msg.dict_len == 0:
@@ -412,7 +414,7 @@ class Kmsg_5_10_to_(ABCKmsg):
     def symtab_checks(cls, vmlinux) -> bool:
         return vmlinux.has_symbol("prb")
 
-    def get_text_from_data_ring(self, text_data_ring, desc, info) -> str:
+    def get_text_from_data_ring(self, text_data_ring, desc, info) -> Union[str, None]:
         text_data_sz = text_data_ring.size_bits
         text_data_mask = 1 << text_data_sz
 
@@ -440,7 +442,8 @@ class Kmsg_5_10_to_(ABCKmsg):
 
     def get_log_lines(self, text_data_ring, desc, info) -> Generator[str, None, None]:
         text = self.get_text_from_data_ring(text_data_ring, desc, info)
-        yield from text.splitlines()
+        if text:
+            yield from text.splitlines()
 
     def get_dict_lines(self, info) -> Generator[str, None, None]:
         dict_text = utility.array_to_string(info.dev_info.subsystem)