trace: dmesg: Allow using old util-linux binary

Old util-linux binaries don't support --force-prefix. Multi-line entry
parsing will break on these, but at least we can collect the log.

Also decode the raw priority, so only the facility is not decoded in
case busybox or old util-linux is used.

devlib/trace/dmesg.py

@@ -39,6 +39,8 @@ class KernelLogEntry(object):
     """
 
     _TIMESTAMP_MSG_REGEX = re.compile(r'\[(.*?)\] (.*)')
+    _RAW_LEVEL_REGEX = re.compile(r'<([0-9]+)>(.*)')
+    _PRETTY_LEVEL_REGEX = re.compile(r'\s*([a-z]+)\s*:([a-z]+)\s*:\s*(.*)')
 
     def __init__(self, facility, level, timestamp, msg):
         self.facility = facility
@@ -52,50 +54,57 @@ class KernelLogEntry(object):
         Parses a "dmesg --decode" output line, formatted as following:
         kern  :err   : [3618282.310743] nouveau 0000:01:00.0: systemd-logind[988]: nv50cal_space: -16
 
-        Or the more basic output:
-        [3618282.310743] nouveau 0000:01:00.0: systemd-logind[988]: nv50cal_space: -16
+        Or the more basic output given by "dmesg -r":
+        <3>[3618282.310743] nouveau 0000:01:00.0: systemd-logind[988]: nv50cal_space: -16
 
         """
 
-        def parse_timestamp_msg(line):
-            match = cls._TIMESTAMP_MSG_REGEX.match(line.strip())
+        def parse_raw_level(line):
+            match = cls._RAW_LEVEL_REGEX.match(line)
             if not match:
                 raise ValueError('dmesg entry format not recognized: {}'.format(line))
+            level, remainder = match.groups()
+            levels = DmesgCollector.LOG_LEVELS
+            # BusyBox dmesg can output numbers that need to wrap around
+            level = levels[int(level) % len(levels)]
+            return level, remainder
+
+        def parse_pretty_level(line):
+            match = cls._PRETTY_LEVEL_REGEX.match(line)
+            facility, level, remainder = match.groups()
+            return facility, level, remainder
+
+        def parse_timestamp_msg(line):
+            match = cls._TIMESTAMP_MSG_REGEX.match(line)
             timestamp, msg = match.groups()
+            timestamp = timedelta(seconds=float(timestamp.strip()))
             return timestamp, msg
 
-        # If we can parse the timestamp directly, that is a basic line
+        line = line.strip()
+
+        # If we can parse the raw prio directly, that is a basic line
         try:
-            timestamp, msg = parse_timestamp_msg(line)
-        except ValueError:
-            facility, level, remainder = line.split(':', 2)
-            timestamp, msg = parse_timestamp_msg(remainder)
-            facility = facility.strip()
-            level = level.strip()
-        else:
+            level, remainder = parse_raw_level(line)
             facility = None
-            level = None
+        except ValueError:
+            facility, level, remainder = parse_pretty_level(line)
+
+        timestamp, msg = parse_timestamp_msg(remainder)
 
         return cls(
             facility=facility,
             level=level,
-            timestamp=timedelta(seconds=float(timestamp.strip())),
+            timestamp=timestamp,
             msg=msg.strip(),
         )
 
     def __str__(self):
-        if self.facility and self.level:
-            prefix = '{facility}:{level}:'.format(
-                facility=self.facility,
-                level=self.level,
-            )
-        else:
-            prefix = ''
-
-        return '{prefix}[{timestamp}] {msg}'.format(
+        facility = self.facility + ': ' if self.facility else ''
+        return '{facility}{level}: [{timestamp}] {msg}'.format(
+            facility=facility,
+            level=self.level,
             timestamp=self.timestamp.total_seconds(),
             msg=self.msg,
-            prefix=prefix,
         )
 
 
@@ -136,11 +145,12 @@ class DmesgCollector(TraceCollector):
             ))
         self.level = level
 
-        # Check if dmesg is the BusyBox one, or the one from util-linux.
+        # Check if dmesg is the BusyBox one, or the one from util-linux in a
+        # recent version.
         # Note: BusyBox dmesg does not support -h, but will still print the
         # help with an exit code of 1
-        self.basic_dmesg = 'BusyBox' in self.target.execute('dmesg -h',
-                                                        check_exit_code=False)
+        self.basic_dmesg = '--force-prefix' not in \
+                self.target.execute('dmesg -h', check_exit_code=False)
         self.facility = facility
         self.reset()
 
@@ -173,7 +183,7 @@ class DmesgCollector(TraceCollector):
         ))
         levels_list.append(self.level)
         if self.basic_dmesg:
-            cmd = 'dmesg'
+            cmd = 'dmesg -r'
         else:
             cmd = 'dmesg --facility={facility} --force-prefix --decode --level={levels}'.format(
                 levels=','.join(levels_list),