ftrace: Use named ftrace buffer

Use a buffer named "devlib" instead of using the top-level default
buffer. That will improve interop with other tools trying to collect a
trace at the same time as devlib.

Author: douglas-raillard-arm

devlib/collector/ftrace.py

@@ -237,7 +237,7 @@ def available_functions(self):
         return self.target.read_value(self.available_functions_file).splitlines()
 
     def reset(self):
-        self.target.execute('{} reset'.format(self.target_binary),
+        self.target.execute('{} reset -B devlib'.format(self.target_binary),
                             as_root=True, timeout=TIMEOUT)
         if self.functions:
             self.target.write_value(self.function_profile_file, 0, verify=False)
@@ -262,7 +262,7 @@ async def start(self):
             self.target.write_value('/proc/sys/kernel/kptr_restrict', 0)
 
         self.target.execute(
-            '{} start {buffer_size} {cmdlines_size} {clock} {events} {tracer} {functions}'.format(
+            '{} start -B devlib {buffer_size} {cmdlines_size} {clock} {events} {tracer} {functions}'.format(
                 self.target_binary,
                 events=self.event_string,
                 tracer=tracer_string,
@@ -307,7 +307,7 @@ def stop(self):
         self.stop_time = time.time()
         if self.automark:
             self.mark_stop()
-        self.target.execute('{} stop'.format(self.target_binary),
+        self.target.execute('{} stop -B devlib'.format(self.target_binary),
                             timeout=TIMEOUT, as_root=True)
         self._reset_needed = True