Modify tools/ext4dist.py for 4.10+ (iovisor#1855)

based on kernel version, different kernel functions are kprobed.

tools/ext4dist.py

@@ -174,7 +174,16 @@
 b = BPF(text=bpf_text)
 
 # Common file functions. See earlier comment about generic_file_read_iter().
-b.attach_kprobe(event="generic_file_read_iter", fn_name="trace_read_entry")
+# 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,
+# 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'):
+ 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")
 b.attach_kprobe(event="ext4_file_write_iter", fn_name="trace_entry")
 b.attach_kprobe(event="ext4_file_open", fn_name="trace_entry")
 b.attach_kprobe(event="ext4_sync_file", fn_name="trace_entry")