Re: [Qemu-devel] [PATCH 2/4] trace: Direct access of atomics is verboten, use the API

[Harsh Bora]

On 01/25/2013 09:13 PM, Markus Armbruster wrote:

The GLib Reference Manual says:

     It is very important that all accesses to a particular integer or
     pointer be performed using only this API and that different sizes
     of operation are not mixed or used on overlapping memory
     regions. Never read or assign directly from or to a value --
     always use this API.

Signed-off-by: Markus Armbruster <arm...@redhat.com>

Reviewed-by: Harsh Prateek Bora <ha...@linux.vnet.ibm.com>

---
  trace/simple.c | 9 +++++----
  1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/trace/simple.c b/trace/simple.c
index ccbdb6a..592ff48 100644
--- a/trace/simple.c
+++ b/trace/simple.c
@@ -166,13 +166,13 @@ static gpointer writeout_thread(gpointer opaque)
      for (;;) {
          wait_for_trace_records_available();

-        if (dropped_events) {
+        if (g_atomic_int_get(&dropped_events)) {
              dropped.rec.event = DROPPED_EVENT_ID,
              dropped.rec.timestamp_ns = get_clock();
              dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t),
              dropped.rec.reserved = 0;
              while (1) {
-                dropped_count = dropped_events;
+                dropped_count = g_atomic_int_get(&dropped_events);
                  if (g_atomic_int_compare_and_exchange(&dropped_events,
                                                        dropped_count, 0)) {
                      break;
@@ -214,7 +214,7 @@ int trace_record_start(TraceBufferRecord *rec, TraceEventID 
event, size_t datasi
      uint64_t timestamp_ns = get_clock();

      while (1) {
-        old_idx = trace_idx;
+        old_idx = g_atomic_int_get(&trace_idx);
          smp_rmb();
          new_idx = old_idx + rec_len;

@@ -275,7 +275,8 @@ void trace_record_finish(TraceBufferRecord *rec)
      record.event |= TRACE_RECORD_VALID;
      write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));

-    if ((trace_idx - writeout_idx) > TRACE_BUF_FLUSH_THRESHOLD) {
+    if ((g_atomic_int_get(&trace_idx) - writeout_idx)
+        > TRACE_BUF_FLUSH_THRESHOLD) {
          flush_trace_file(false);
      }
  }