trace: add trace event iterator APIs

Currently methods which want to iterate over trace events,
do so using the trace_event_count() and trace_event_id()
methods. This leaks the concept of a single ID enum to
the callers. There is an alternative trace_event_pattern()
method which can be used in an iteration context, but its
design is stateless, so is not easy to expand it in the
future.

This defines a formal iterator API will provide a future-
proof way of iterating over events.

The iterator is also able to apply a pattern match filter
to events, further removing the need for the pattern

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Lluís Vilanova <vilanova@ac.upc.edu>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 1475588159-30598-4-git-send-email-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

trace/control.c

@@ -125,6 +125,27 @@ TraceEvent *trace_event_pattern(const char *pat, TraceEvent *ev)
     return NULL;
 }
 
+void trace_event_iter_init(TraceEventIter *iter, const char *pattern)
+{
+    iter->event = 0;
+    iter->pattern = pattern;
+}
+
+TraceEvent *trace_event_iter_next(TraceEventIter *iter)
+{
+    while (iter->event < TRACE_EVENT_COUNT) {
+        TraceEvent *ev = &(trace_events[iter->event]);
+        iter->event++;
+        if (!iter->pattern ||
+            pattern_glob(iter->pattern,
+                         trace_event_get_name(ev))) {
+            return ev;
+        }
+    }
+
+    return NULL;
+}
+
 void trace_list_events(void)
 {
     int i;

trace/control.h

@@ -13,6 +13,10 @@
 #include "qemu-common.h"
 #include "trace/generated-events.h"
 
+typedef struct TraceEventIter {
+    size_t event;
+    const char *pattern;
+} TraceEventIter;
 
 /**
  * TraceEventID:
@@ -25,6 +29,29 @@
  */
 enum TraceEventID;
 
+
+/**
+ * trace_event_iter_init:
+ * @iter: the event iterator struct
+ * @pattern: optional pattern to filter events on name
+ *
+ * Initialize the event iterator struct @iter,
+ * optionally using @pattern to filter out events
+ * with non-matching names.
+ */
+void trace_event_iter_init(TraceEventIter *iter, const char *pattern);
+
+/**
+ * trace_event_iter_next:
+ * @iter: the event iterator struct
+ *
+ * Get the next event, if any. When this returns NULL,
+ * the iterator should no longer be used.
+ *
+ * Returns: the next event, or NULL if no more events exist
+ */
+TraceEvent *trace_event_iter_next(TraceEventIter *iter);
+
 /**
  * trace_event_id:
  * @id: Event identifier.