2 files changed, 8 insertions, 4 deletions
diff --git a/runtime/probes/test4/README b/runtime/probes/test4/README
index 20a1ad23..75d4be10 100644
--- a/runtime/probes/test4/README
+++ b/runtime/probes/test4/README
@@ -1,7 +1,9 @@
-Sample probe.
-
-This is a translation of on an old dtr probe:
+/** @dir test4
+This example probe tracks file opens, reads and writes.
+It demonstrates maps, stats, and iterators.
 
+This is a translation of on an old dtr probe.  Original source is
+\verbatim
 global {
   long @opens[string];
   sum @reads[string], @writes[string];
@@ -18,3 +20,5 @@ probe sys_read:entry {
 probe sys_write:entry {
   @writes[current->comm] << count;
 }
+\endverbatim
+*/
diff --git a/runtime/probes/test4/dtr.c b/runtime/probes/test4/dtr.c
index 1c8d8f05..8c6257e2 100644
--- a/runtime/probes/test4/dtr.c
+++ b/runtime/probes/test4/dtr.c
@@ -15,7 +15,7 @@ MAP opens, reads, writes;
 asmlinkage long inst_sys_open (const char __user * filename, int flags, int mode)
 {
   _stp_map_key_str (opens, current->comm);
-  _stp_map_set_int64 (opens, _stp_map_get_int64(opens) + 1);
+  _stp_map_add_int64 (opens, 1);
   jprobe_return();
   return 0;
 }