Pull request

- Mads Ynddal's improvements to simpletrace.py
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Merge tag 'tracing-pull-request' of https://gitlab.com/stefanha/qemu into staging

Pull request

- Mads Ynddal's improvements to simpletrace.py

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# gpg: Signature made Thu 28 Sep 2023 09:44:00 EDT
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [ultimate]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [ultimate]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* tag 'tracing-pull-request' of https://gitlab.com/stefanha/qemu:
  scripts/analyse-locks-simpletrace.py: changed iteritems() to items()
  MAINTAINERS: add maintainer of simpletrace.py
  simpletrace: added simplified Analyzer2 class
  simpletrace: move event processing to Analyzer class
  simpletrace: move logic of process into internal function
  simpletrace: refactor to separate responsibilities
  simpletrace: made Analyzer into context-manager
  simpletrace: define exception and add handling
  simpletrace: improved error handling on struct unpack
  simpletrace: update code for Python 3.11
  simpletrace: changed naming of edict and idtoname to improve readability
  simpletrace: improve parsing of sys.argv; fix files never closed.
  simpletrace: annotate magic constants from QEMU code
  simpletrace: add __all__ to define public interface

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

MAINTAINERS

@@ -3170,6 +3170,7 @@ F: stubs/
 
 Tracing
 M: Stefan Hajnoczi <stefanha@redhat.com>
+R: Mads Ynddal <mads@ynddal.dk>
 S: Maintained
 F: trace/
 F: trace-events
@@ -3182,6 +3183,11 @@ F: docs/tools/qemu-trace-stap.rst
 F: docs/devel/tracing.rst
 T: git https://github.com/stefanha/qemu.git tracing
 
+Simpletrace
+M: Mads Ynddal <mads@ynddal.dk>
+S: Maintained
+F: scripts/simpletrace.py
+
 TPM
 M: Stefan Berger <stefanb@linux.ibm.com>
 S: Maintained

scripts/analyse-locks-simpletrace.py

@@ -75,7 +75,7 @@ if __name__ == '__main__':
            (analyser.locks, analyser.locked, analyser.unlocks))
 
     # Now dump the individual lock stats
-    for key, val in sorted(analyser.mutex_records.iteritems(),
+    for key, val in sorted(analyser.mutex_records.items(),
                            key=lambda k_v: k_v[1]["locks"]):
         print ("Lock: %#x locks: %d, locked: %d, unlocked: %d" %
                (key, val["locks"], val["locked"], val["unlocked"]))

scripts/simpletrace.py

@@ -9,11 +9,20 @@
 #
 # For help see docs/devel/tracing.rst
 
+import sys
 import struct
 import inspect
+import warnings
 from tracetool import read_events, Event
 from tracetool.backend.simple import is_string
 
+__all__ = ['Analyzer', 'Analyzer2', 'process', 'run']
+
+# This is the binary format that the QEMU "simple" trace backend
+# emits. There is no specification documentation because the format is
+# not guaranteed to be stable. Trace files must be parsed with the
+# same trace-events-all file and the same simpletrace.py file that
+# QEMU was built with.
 header_event_id = 0xffffffffffffffff
 header_magic    = 0xf2b177cb0aa429b4
 dropped_event_id = 0xfffffffffffffffe
@@ -23,48 +32,19 @@ record_type_event = 1
 
 log_header_fmt = '=QQQ'
 rec_header_fmt = '=QQII'
+rec_header_fmt_len = struct.calcsize(rec_header_fmt)
+
+class SimpleException(Exception):
+    pass
 
 def read_header(fobj, hfmt):
     '''Read a trace record header'''
     hlen = struct.calcsize(hfmt)
     hdr = fobj.read(hlen)
     if len(hdr) != hlen:
-        return None
+        raise SimpleException('Error reading header. Wrong filetype provided?')
     return struct.unpack(hfmt, hdr)
 
-def get_record(edict, idtoname, rechdr, fobj):
-    """Deserialize a trace record from a file into a tuple
-       (name, timestamp, pid, arg1, ..., arg6)."""
-    if rechdr is None:
-        return None
-    if rechdr[0] != dropped_event_id:
-        event_id = rechdr[0]
-        name = idtoname[event_id]
-        rec = (name, rechdr[1], rechdr[3])
-        try:
-            event = edict[name]
-        except KeyError as e:
-            import sys
-            sys.stderr.write('%s event is logged but is not declared ' \
-                             'in the trace events file, try using ' \
-                             'trace-events-all instead.\n' % str(e))
-            sys.exit(1)
-
-        for type, name in event.args:
-            if is_string(type):
-                l = fobj.read(4)
-                (len,) = struct.unpack('=L', l)
-                s = fobj.read(len)
-                rec = rec + (s,)
-            else:
-                (value,) = struct.unpack('=Q', fobj.read(8))
-                rec = rec + (value,)
-    else:
-        rec = ("dropped", rechdr[1], rechdr[3])
-        (value,) = struct.unpack('=Q', fobj.read(8))
-        rec = rec + (value,)
-    return rec
-
 def get_mapping(fobj):
     (event_id, ) = struct.unpack('=Q', fobj.read(8))
     (len, ) = struct.unpack('=L', fobj.read(4))
@@ -72,41 +52,47 @@ def get_mapping(fobj):
 
     return (event_id, name)
 
-def read_record(edict, idtoname, fobj):
+def read_record(fobj):
-    """Deserialize a trace record from a file into a tuple (event_num, timestamp, pid, arg1, ..., arg6)."""
+    """Deserialize a trace record from a file into a tuple (event_num, timestamp, pid, args)."""
-    rechdr = read_header(fobj, rec_header_fmt)
+    event_id, timestamp_ns, record_length, record_pid = read_header(fobj, rec_header_fmt)
-    return get_record(edict, idtoname, rechdr, fobj)
+    args_payload = fobj.read(record_length - rec_header_fmt_len)
+    return (event_id, timestamp_ns, record_pid, args_payload)
 
 def read_trace_header(fobj):
     """Read and verify trace file header"""
-    header = read_header(fobj, log_header_fmt)
+    _header_event_id, _header_magic, log_version = read_header(fobj, log_header_fmt)
-    if header is None:
+    if _header_event_id != header_event_id:
-        raise ValueError('Not a valid trace file!')
+        raise ValueError(f'Not a valid trace file, header id {_header_event_id} != {header_event_id}')
-    if header[0] != header_event_id:
+    if _header_magic != header_magic:
-        raise ValueError('Not a valid trace file, header id %d != %d' %
+        raise ValueError(f'Not a valid trace file, header magic {_header_magic} != {header_magic}')
-                         (header[0], header_event_id))
-    if header[1] != header_magic:
-        raise ValueError('Not a valid trace file, header magic %d != %d' %
-                         (header[1], header_magic))
 
-    log_version = header[2]
     if log_version not in [0, 2, 3, 4]:
-        raise ValueError('Unknown version of tracelog format!')
+        raise ValueError(f'Unknown version {log_version} of tracelog format!')
     if log_version != 4:
-        raise ValueError('Log format %d not supported with this QEMU release!'
+        raise ValueError(f'Log format {log_version} not supported with this QEMU release!')
-                         % log_version)
 
-def read_trace_records(edict, idtoname, fobj):
+def read_trace_records(events, fobj, read_header):
-    """Deserialize trace records from a file, yielding record tuples (event_num, timestamp, pid, arg1, ..., arg6).
+    """Deserialize trace records from a file, yielding record tuples (event, event_num, timestamp, pid, arg1, ..., arg6).
-
-    Note that `idtoname` is modified if the file contains mapping records.
 
     Args:
-        edict (str -> Event): events dict, indexed by name
+        event_mapping (str -> Event): events dict, indexed by name
-        idtoname (int -> str): event names dict, indexed by event ID
         fobj (file): input file
+        read_header (bool): whether headers were read from fobj
 
     """
+    frameinfo = inspect.getframeinfo(inspect.currentframe())
+    dropped_event = Event.build("Dropped_Event(uint64_t num_events_dropped)",
+                                frameinfo.lineno + 1, frameinfo.filename)
+
+    event_mapping = {e.name: e for e in events}
+    event_mapping["dropped"] = dropped_event
+    event_id_to_name = {dropped_event_id: "dropped"}
+
+    # If there is no header assume event ID mapping matches events list
+    if not read_header:
+        for event_id, event in enumerate(events):
+            event_id_to_name[event_id] = event.name
+
     while True:
         t = fobj.read(8)
         if len(t) == 0:
@@ -114,19 +100,45 @@ def read_trace_records(edict, idtoname, fobj):
 
         (rectype, ) = struct.unpack('=Q', t)
         if rectype == record_type_mapping:
-            event_id, name = get_mapping(fobj)
+            event_id, event_name = get_mapping(fobj)
-            idtoname[event_id] = name
+            event_id_to_name[event_id] = event_name
         else:
-            rec = read_record(edict, idtoname, fobj)
+            event_id, timestamp_ns, pid, args_payload = read_record(fobj)
+            event_name = event_id_to_name[event_id]
 
-            yield rec
+            try:
+                event = event_mapping[event_name]
+            except KeyError as e:
+                raise SimpleException(
+                    f'{e} event is logged but is not declared in the trace events'
+                    'file, try using trace-events-all instead.'
+                )
 
-class Analyzer(object):
+            offset = 0
-    """A trace file analyzer which processes trace records.
+            args = []
+            for type, _ in event.args:
+                if is_string(type):
+                    (length,) = struct.unpack_from('=L', args_payload, offset=offset)
+                    offset += 4
+                    s = args_payload[offset:offset+length]
+                    offset += length
+                    args.append(s)
+                else:
+                    (value,) = struct.unpack_from('=Q', args_payload, offset=offset)
+                    offset += 8
+                    args.append(value)
+
+            yield (event_mapping[event_name], event_name, timestamp_ns, pid) + tuple(args)
+
+class Analyzer:
+    """[Deprecated. Refer to Analyzer2 instead.]
+
+    A trace file analyzer which processes trace records.
 
     An analyzer can be passed to run() or process().  The begin() method is
     invoked, then each trace record is processed, and finally the end() method
-    is invoked.
+    is invoked. When Analyzer is used as a context-manager (using the `with`
+    statement), begin() and end() are called automatically.
 
     If a method matching a trace event name exists, it is invoked to process
     that trace record.  Otherwise the catchall() method is invoked.
@@ -160,44 +172,14 @@ class Analyzer(object):
         """Called if no specific method for processing a trace event has been found."""
         pass
 
-    def end(self):
+    def _build_fn(self, event):
-        """Called at the end of the trace."""
+        fn = getattr(self, event.name, None)
-        pass
-
-def process(events, log, analyzer, read_header=True):
-    """Invoke an analyzer on each event in a log."""
-    if isinstance(events, str):
-        events = read_events(open(events, 'r'), events)
-    if isinstance(log, str):
-        log = open(log, 'rb')
-
-    if read_header:
-        read_trace_header(log)
-
-    frameinfo = inspect.getframeinfo(inspect.currentframe())
-    dropped_event = Event.build("Dropped_Event(uint64_t num_events_dropped)",
-                                frameinfo.lineno + 1, frameinfo.filename)
-    edict = {"dropped": dropped_event}
-    idtoname = {dropped_event_id: "dropped"}
-
-    for event in events:
-        edict[event.name] = event
-
-    # If there is no header assume event ID mapping matches events list
-    if not read_header:
-        for event_id, event in enumerate(events):
-            idtoname[event_id] = event.name
-
-    def build_fn(analyzer, event):
-        if isinstance(event, str):
-            return analyzer.catchall
-
-        fn = getattr(analyzer, event.name, None)
         if fn is None:
-            return analyzer.catchall
+            # Return early to avoid costly call to inspect.getfullargspec
+            return self.catchall
 
         event_argcount = len(event.args)
-        fn_argcount = len(inspect.getargspec(fn)[0]) - 1
+        fn_argcount = len(inspect.getfullargspec(fn)[0]) - 1
         if fn_argcount == event_argcount + 1:
             # Include timestamp as first argument
             return lambda _, rec: fn(*(rec[1:2] + rec[3:3 + event_argcount]))
@@ -208,56 +190,170 @@ def process(events, log, analyzer, read_header=True):
             # Just arguments, no timestamp or pid
             return lambda _, rec: fn(*rec[3:3 + event_argcount])
 
-    analyzer.begin()
+    def _process_event(self, rec_args, *, event, event_id, timestamp_ns, pid, **kwargs):
-    fn_cache = {}
+        warnings.warn(
-    for rec in read_trace_records(edict, idtoname, log):
+            "Use of deprecated Analyzer class. Refer to Analyzer2 instead.",
-        event_num = rec[0]
+            DeprecationWarning,
-        event = edict[event_num]
+        )
-        if event_num not in fn_cache:
+
-            fn_cache[event_num] = build_fn(analyzer, event)
+        if not hasattr(self, '_fn_cache'):
-        fn_cache[event_num](event, rec)
+            # NOTE: Cannot depend on downstream subclasses to have
-    analyzer.end()
+            # super().__init__() because of legacy.
+            self._fn_cache = {}
+
+        rec = (event_id, timestamp_ns, pid, *rec_args)
+        if event_id not in self._fn_cache:
+            self._fn_cache[event_id] = self._build_fn(event)
+        self._fn_cache[event_id](event, rec)
+
+    def end(self):
+        """Called at the end of the trace."""
+        pass
+
+    def __enter__(self):
+        self.begin()
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        if exc_type is None:
+            self.end()
+        return False
+
+class Analyzer2(Analyzer):
+    """A trace file analyzer which processes trace records.
+
+    An analyzer can be passed to run() or process().  The begin() method is
+    invoked, then each trace record is processed, and finally the end() method
+    is invoked. When Analyzer is used as a context-manager (using the `with`
+    statement), begin() and end() are called automatically.
+
+    If a method matching a trace event name exists, it is invoked to process
+    that trace record.  Otherwise the catchall() method is invoked.
+
+    The methods are called with a set of keyword-arguments. These can be ignored
+    using `**kwargs` or defined like any keyword-argument.
+
+    The following keyword-arguments are available, but make sure to have an
+    **kwargs to allow for unmatched arguments in the future:
+        event: Event object of current trace
+        event_id: The id of the event in the current trace file
+        timestamp_ns: The timestamp in nanoseconds of the trace
+        pid: The process id recorded for the given trace
+
+    Example:
+    The following method handles the runstate_set(int new_state) trace event::
+
+      def runstate_set(self, new_state, **kwargs):
+          ...
+
+    The method can also explicitly take a timestamp keyword-argument with the
+    trace event arguments::
+
+      def runstate_set(self, new_state, *, timestamp_ns, **kwargs):
+          ...
+
+    Timestamps have the uint64_t type and are in nanoseconds.
+
+    The pid can be included in addition to the timestamp and is useful when
+    dealing with traces from multiple processes:
+
+      def runstate_set(self, new_state, *, timestamp_ns, pid, **kwargs):
+          ...
+    """
+
+    def catchall(self, *rec_args, event, timestamp_ns, pid, event_id, **kwargs):
+        """Called if no specific method for processing a trace event has been found."""
+        pass
+
+    def _process_event(self, rec_args, *, event, **kwargs):
+        fn = getattr(self, event.name, self.catchall)
+        fn(*rec_args, event=event, **kwargs)
+
+def process(events, log, analyzer, read_header=True):
+    """Invoke an analyzer on each event in a log.
+    Args:
+        events (file-object or list or str): events list or file-like object or file path as str to read event data from
+        log (file-object or str): file-like object or file path as str to read log data from
+        analyzer (Analyzer): Instance of Analyzer to interpret the event data
+        read_header (bool, optional): Whether to read header data from the log data. Defaults to True.
+    """
+
+    if isinstance(events, str):
+        with open(events, 'r') as f:
+            events_list = read_events(f, events)
+    elif isinstance(events, list):
+        # Treat as a list of events already produced by tracetool.read_events
+        events_list = events
+    else:
+        # Treat as an already opened file-object
+        events_list = read_events(events, events.name)
+
+    if isinstance(log, str):
+        with open(log, 'rb') as log_fobj:
+            _process(events_list, log_fobj, analyzer, read_header)
+    else:
+        # Treat `log` as an already opened file-object. We will not close it,
+        # as we do not own it.
+        _process(events_list, log, analyzer, read_header)
+
+def _process(events, log_fobj, analyzer, read_header=True):
+    """Internal function for processing
+
+    Args:
+        events (list): list of events already produced by tracetool.read_events
+        log_fobj (file): file-object to read log data from
+        analyzer (Analyzer): the Analyzer to interpret the event data
+        read_header (bool, optional): Whether to read header data from the log data. Defaults to True.
+    """
+
+    if read_header:
+        read_trace_header(log_fobj)
+
+    with analyzer:
+        for event, event_id, timestamp_ns, record_pid, *rec_args in read_trace_records(events, log_fobj, read_header):
+            analyzer._process_event(
+                rec_args,
+                event=event,
+                event_id=event_id,
+                timestamp_ns=timestamp_ns,
+                pid=record_pid,
+            )
 
 def run(analyzer):
     """Execute an analyzer on a trace file given on the command-line.
 
     This function is useful as a driver for simple analysis scripts.  More
     advanced scripts will want to call process() instead."""
-    import sys
 
-    read_header = True
+    try:
-    if len(sys.argv) == 4 and sys.argv[1] == '--no-header':
+        # NOTE: See built-in `argparse` module for a more robust cli interface
-        read_header = False
+        *no_header, trace_event_path, trace_file_path = sys.argv[1:]
-        del sys.argv[1]
+        assert no_header == [] or no_header == ['--no-header'], 'Invalid no-header argument'
-    elif len(sys.argv) != 3:
+    except (AssertionError, ValueError):
-        sys.stderr.write('usage: %s [--no-header] <trace-events> ' \
+        raise SimpleException(f'usage: {sys.argv[0]} [--no-header] <trace-events> <trace-file>\n')
-                         '<trace-file>\n' % sys.argv[0])
-        sys.exit(1)
 
-    events = read_events(open(sys.argv[1], 'r'), sys.argv[1])
+    with open(trace_event_path, 'r') as events_fobj, open(trace_file_path, 'rb') as log_fobj:
-    process(events, sys.argv[2], analyzer, read_header=read_header)
+        process(events_fobj, log_fobj, analyzer, read_header=not no_header)
 
 if __name__ == '__main__':
-    class Formatter(Analyzer):
+    class Formatter2(Analyzer2):
         def __init__(self):
-            self.last_timestamp = None
+            self.last_timestamp_ns = None
 
-        def catchall(self, event, rec):
+        def catchall(self, *rec_args, event, timestamp_ns, pid, event_id):
-            timestamp = rec[1]
+            if self.last_timestamp_ns is None:
-            if self.last_timestamp is None:
+                self.last_timestamp_ns = timestamp_ns
-                self.last_timestamp = timestamp
+            delta_ns = timestamp_ns - self.last_timestamp_ns
-            delta_ns = timestamp - self.last_timestamp
+            self.last_timestamp_ns = timestamp_ns
-            self.last_timestamp = timestamp
 
-            fields = [event.name, '%0.3f' % (delta_ns / 1000.0),
+            fields = [
-                      'pid=%d' % rec[2]]
+                f'{name}={r}' if is_string(type) else f'{name}=0x{r:x}'
-            i = 3
+                for r, (type, name) in zip(rec_args, event.args)
-            for type, name in event.args:
+            ]
-                if is_string(type):
+            print(f'{event.name} {delta_ns / 1000:0.3f} {pid=} ' + ' '.join(fields))
-                    fields.append('%s=%s' % (name, rec[i]))
-                else:
-                    fields.append('%s=0x%x' % (name, rec[i]))
-                i += 1
-            print(' '.join(fields))
 
-    run(Formatter())
+    try:
+        run(Formatter2())
+    except SimpleException as e:
+        sys.stderr.write(str(e) + "\n")
+        sys.exit(1)