ftrace: Support trace-cmd record mode

The current implementation of the FtraceCollector only supports using
ftrace in its start-stop mode which keeps the traces in memory and then
writes to file at the end. Trace-cmd also supports a different mode -
record which writes to file periodically meaning that it allows
recording traces that would exceed the 'start' mode buffer size in
exchange for added noise.

This commit adds support for selecting which mode trace-cmd should be
run in. It adds a new collector parameter - 'trace_cmd_mode' which is
used to distinguish between the two approaches.

While at it, it also cleans up the collector in some places, e.g. the
teardown() method.

Signed-off-by: Kajetan Puchalski <[email protected]>

devlib/collector/ftrace.py

@@ -19,6 +19,7 @@
 import re
 import subprocess
 import sys
+import signal
 import contextlib
 from shlex import quote
 
@@ -51,6 +52,7 @@
 CPU_RE = re.compile(r'  Function \(CPU([0-9]+)\)')
 STATS_RE = re.compile(r'([^ ]*) +([0-9]+) +([0-9.]+) us +([0-9.]+) us +([0-9.]+) us')
 
+
 class FtraceCollector(CollectorBase):
 
     # pylint: disable=too-many-locals,too-many-branches,too-many-statements
@@ -71,6 +73,7 @@ def __init__(self, target,
                  report_on_target=False,
                  trace_clock='local',
                  saved_cmdlines_nr=4096,
+                 trace_cmd_mode='start',
                  ):
         super(FtraceCollector, self).__init__(target)
         self.events = events if events is not None else DEFAULT_EVENTS
@@ -85,6 +88,7 @@ def __init__(self, target,
         self.autoview = autoview
         self.strict = strict
         self.report_on_target = report_on_target
+        self.trace_cmd_mode = trace_cmd_mode
         self.target_output_file = target.path.join(self.target.working_directory, OUTPUT_TRACE_FILE)
         text_file_name = target.path.splitext(OUTPUT_TRACE_FILE)[0] + '.txt'
         self.target_text_file = target.path.join(self.target.working_directory, text_file_name)
@@ -98,6 +102,8 @@ def __init__(self, target,
         self.trace_clock = trace_clock
         self.saved_cmdlines_nr = saved_cmdlines_nr
         self._reset_needed = True
+        self.bg_cmd = None
+        self.tmp_output_dir = None
 
         # pylint: disable=bad-whitespace
         # Setup tracing paths
@@ -276,18 +282,35 @@ async def start(self):
         with contextlib.suppress(TargetStableError):
             self.target.write_value('/proc/sys/kernel/kptr_restrict', 0)
 
-        self.target.execute(
-            '{} start -B devlib {buffer_size} {cmdlines_size} {clock} {events} {tracer} {functions}'.format(
-                self.target_binary,
-                events=self.event_string,
-                tracer=tracer_string,
-                functions=tracecmd_functions,
-                buffer_size='-b {}'.format(self.buffer_size) if self.buffer_size is not None else '',
-                clock='-C {}'.format(self.trace_clock) if self.trace_clock else '',
-                cmdlines_size='--cmdlines-size {}'.format(self.saved_cmdlines_nr) if self.saved_cmdlines_nr is not None else '',
-            ),
-            as_root=True,
+        trace_cmd = '{} {command} -B devlib {buffer_size} {cmdlines_size} {clock} {events} {tracer} {functions}'.format(
+            self.target_binary,
+            command=self.trace_cmd_mode,
+            events=self.event_string,
+            tracer=tracer_string,
+            functions=tracecmd_functions,
+            buffer_size='-b {}'.format(self.buffer_size) if self.buffer_size is not None else '',
+            clock='-C {}'.format(self.trace_clock) if self.trace_clock else '',
+            cmdlines_size='--cmdlines-size {}'.format(self.saved_cmdlines_nr) if self.saved_cmdlines_nr is not None else '',
         )
+
+        if self.trace_cmd_mode == 'record':
+            # trace-cmd record needs to be run from a writeable directory
+            self.tmp_output_dir = self.target.execute("{} mktemp -p {output_dir} -d".format(
+                self.target.busybox,
+                output_dir=self.target.working_directory,
+            )).strip()
+            trace_cmd = "cd {} && {command} {output}".format(
+                self.tmp_output_dir,
+                command=trace_cmd,
+                output="-o {}".format(self.target_output_file)
+            )
+            if self.bg_cmd is None:
+                self.bg_cmd = self.target.background(trace_cmd, as_root=True)
+            else:
+                raise TargetStableError('ftrace collector is not re-entrant')
+        else:
+            self.target.execute(trace_cmd, as_root=True)
+
         if self.automark:
             self.mark_start()
         if 'cpufreq' in self.target.modules:
@@ -310,7 +333,6 @@ async def start(self):
                                     as_root=True),
             )
 
-
     def stop(self):
         # Disable kernel function profiling
         if self.functions and self.tracer is None:
@@ -322,8 +344,11 @@ def stop(self):
         self.stop_time = time.time()
         if self.automark:
             self.mark_stop()
-        self.target.execute('{} stop -B devlib'.format(self.target_binary),
-                            timeout=TIMEOUT, as_root=True)
+        if self.trace_cmd_mode == 'record':
+            self.bg_cmd.send_signal(signal.SIGINT)
+            self.bg_cmd = None
+        else:
+            self.target.execute('{} stop -B devlib'.format(self.target_binary), timeout=TIMEOUT, as_root=True)
         self._reset_needed = True
 
     def set_output(self, output_path):
@@ -334,15 +359,13 @@ def set_output(self, output_path):
     def get_data(self):
         if self.output_path is None:
             raise RuntimeError("Output path was not set.")
-        self.target.execute('{0} extract -B devlib -o {1}; chmod 666 {1}'.format(self.target_binary,
-                                                                       self.target_output_file),
-                            timeout=TIMEOUT, as_root=True)
-
-        # The size of trace.dat will depend on how long trace-cmd was running.
-        # Therefore timout for the pull command must also be adjusted
-        # accordingly.
-        pull_timeout = 10 * (self.stop_time - self.start_time)
-        self.target.pull(self.target_output_file, self.output_path, timeout=pull_timeout)
+
+        if self.trace_cmd_mode == 'start':
+            self.target.execute('{0} extract -B devlib -o {1}; chmod 666 {1}'.format(
+                self.target_binary, self.target_output_file
+            ), timeout=TIMEOUT, as_root=True)
+
+        self.target.pull(self.target_output_file, self.output_path)
         output = CollectorOutput()
         if not os.path.isfile(self.output_path):
             self.logger.warning('Binary trace not pulled from device.')
@@ -440,7 +463,11 @@ def view(self, binfile):
         check_output('{} {}'.format(self.kernelshark, binfile), shell=True)
 
     def teardown(self):
-        self.target.remove(self.target.path.join(self.target.working_directory, OUTPUT_TRACE_FILE))
+        self.target.remove(self.target_output_file)
+        if self.report_on_target:
+            self.target.remove(self.target_text_file)
+        if self.tmp_output_dir is not None:
+            self.target.remove(self.tmp_output_dir)
 
     def mark_start(self):
         self.target.write_value(self.marker_file, TRACE_MARKER_START, verify=False)