[Qemu-devel] [PATCH v3 1/2] Add a simple mechanism to protect against error message floods.

["Richard W.M. Jones" <rjones@redhat.com>]

You can now write code like this:

  FLOOD_COUNTER(errcount, 100);
  ...
  NO_FLOOD(errcount,
           error_report("oops, something bad happened"),
           error_report("further errors suppressed"));

which would print the "oops, ..." error message up to 100 times,
followed by the "further errors suppressed" message once, and then
nothing else.

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 include/qemu/no-flood.h | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 include/qemu/no-flood.h

diff --git a/include/qemu/no-flood.h b/include/qemu/no-flood.h
new file mode 100644
index 0000000..90a24da
--- /dev/null
+++ b/include/qemu/no-flood.h
@@ -0,0 +1,34 @@
+/*
+ * Suppress error floods.
+ *
+ * Copyright (C) 2015 Red Hat, Inc.
+ *
+ * Author: Richard W.M. Jones <rjones@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef __QEMU_NO_FLOOD_H
+#define __QEMU_NO_FLOOD_H 1
+
+#include "qemu/atomic.h"
+
+/* Suggested initial value is 100 */
+#define FLOOD_COUNTER(counter_name, initial) \
+  static int counter_name = (initial)
+
+#define NO_FLOOD(counter_name, code, suppress_message)         \
+  do {                                                         \
+    int t_##counter_name = atomic_fetch_add(&counter_name, 0); \
+    if (t_##counter_name > 0) {                                \
+        code;                                                  \
+        if (t_##counter_name == 1) {                           \
+            suppress_message;                                  \
+        }                                                      \
+        atomic_dec(&counter_name);                             \
+    }                                                          \
+} while (0)
+
+#endif
-- 
2.3.1