[PATCH 4/4] trace-cruncher: Update 'kprobe_open.py' example

["Yordan Karadzhov (VMware)" <y.karadz@gmail.com>]

The class kprobe has been refactored. Here we update the corresponding
example accordingly. We also add more comments, explaining the usage
of the APIs.

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
---
 examples/kprobe_open.py | 45 ++++++++++++++++++++++++++++++++---------
 1 file changed, 35 insertions(+), 10 deletions(-)

diff --git a/examples/kprobe_open.py b/examples/kprobe_open.py
index dff4861..141df66 100755
--- a/examples/kprobe_open.py
+++ b/examples/kprobe_open.py
@@ -11,24 +11,42 @@ import sys
 import tracecruncher.ftracepy as ft
 import tracecruncher.ft_utils as tc
 
-open_probe = tc.kprobe(name='open', func='do_sys_openat2')
+# We will define a kprobe event, to be recorded every time the function
+# 'do_sys_openat2' in the kernrl is called.
 
-open_probe.add_string_arg(name='file', param_id=2)
+# Add to the kprobe event a string field 'file', that will record the second
+# argument of the function.
+fields = tc.kprobe_add_string_arg(name='file', param_id=2)
 
-open_probe.add_ptr_arg(name='flags',
-                       param_id=3,
-                       param_type='x64')
+# Add to the kprobe event a field 'flags'. This field will take the third
+# argument of the function, which is a pointer to an object and will convert
+# its starting address into hexadecimal integer. This will decode the first
+# data field of the object.
+fields = tc.kprobe_add_ptr_arg(name='flags',
+                               param_id=3,
+                               param_type='x64',
+                               fields=fields)
 
-open_probe.add_ptr_arg(name='mode',
-                       param_id=3,
-                       param_type='x64',
-                       offset=8)
+# Add to the kprobe event a field 'flags'. This field will take the third
+# argument of the function, which is a pointer to an object and will convert
+# its starting address plus offset of 8 into hexadecimal integer. This will
+# decode the second data field of the object.
+fields = tc.kprobe_add_ptr_arg(name='mode',
+                               param_id=3,
+                               param_type='x64',
+                               offset=8,
+                               fields=fields)
 
-open_probe.register()
+# Create the kprobe event.
+open_probe = tc.kprobe(name='open',
+                       func='do_sys_openat2',
+                       fields=fields)
 
 tep = tc.local_tep()
 tc.short_kprobe_print(tep, [open_probe])
 
+# Define a callback function that will print
+# a short human-readable version.
 def callback(event, record):
     print(tep.info(event, record))
 
@@ -38,6 +56,13 @@ if __name__ == "__main__":
         print('Usage: ', sys.argv[0], ' [PROCESS]')
         sys.exit(1)
 
+    # Create new Ftrace instance to work in. The tracing in this new instance
+    # is not going to be enabled yet.
     inst = ft.create_instance(tracing_on=False)
+
+    # Enable the probe.
     open_probe.enable(instance=inst)
+
+    # Subscribe for the kprobe event (using the default function name 'callback')
+    # and trace the user process.
     ft.trace_process(instance=inst, argv=sys.argv[1:])
-- 
2.32.0