Tools fixes (#2009)

* tools: the argument of get_kprobe_functions() should be a bytes object

It fixes the following error:
Traceback (most recent call last):
  File "/usr/share/bcc/tools/ext4dist", line 189, in <module>
    if BPF.get_kprobe_functions('ext4_file_read_iter'):
  File "/usr/lib/python3.6/site-packages/bcc/__init__.py", line 519, in get_kprobe_functions
    if (t.lower() in [b't', b'w']) and re.match(event_re, fn) \
  File "/usr/lib64/python3.6/re.py", line 172, in match
    return _compile(pattern, flags).match(string)
TypeError: cannot use a string pattern on a bytes-like object

* tools: fix freeze in offwaketime

Since commit 47cecb65, the sigint signal is ignored
unconditionally which prevents offwaketime to be stopped by
pressing Ctrl-C when run without a specified duration.

tools/ext4dist.py

@@ -183,10 +183,10 @@ b = BPF(text=bpf_text)
 # Comment by Joe Yin 
 # From Linux 4.10, the function .read_iter at the ext4_file_operations has 
 # changed to ext4_file_read_iter.
-# So, I add get_kprobe_functions('ext4_file_read_iter'),it will first to attach ext4_file_read_iter,
+# So, I add get_kprobe_functions(b'ext4_file_read_iter'),it will first to attach ext4_file_read_iter,
 # if fails and will attach the generic_file_read_iter which used to pre-4.10.
 
-if BPF.get_kprobe_functions('ext4_file_read_iter'):
+if BPF.get_kprobe_functions(b'ext4_file_read_iter'):
 	b.attach_kprobe(event="ext4_file_read_iter", fn_name="trace_entry")
 else:
 	b.attach_kprobe(event="generic_file_read_iter", fn_name="trace_read_entry")

tools/offwaketime.py

@@ -277,11 +277,13 @@ if not folded:
     else:
         print("... Hit Ctrl-C to end.")
 
-# as cleanup can take many seconds, trap Ctrl-C:
-# print a newline for folded output on Ctrl-C
-signal.signal(signal.SIGINT, signal_ignore)
+try:
+    sleep(duration)
+except KeyboardInterrupt:
+    # as cleanup can take many seconds, trap Ctrl-C:
+    # print a newline for folded output on Ctrl-C
+    signal.signal(signal.SIGINT, signal_ignore)
 
-sleep(duration)
 
 if not folded:
     print()