qemu-error: add {error, warn}_report_once_cond

Add two functions to print an error/warning report once depending
on a passed-in condition variable and flip it if printed. This is
useful if you want to print a message not once-globally, but e.g.
once-per-device.

Inspired by warn_once() in hw/vfio/ccw.c, which has been replaced
with warn_report_once_cond().

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20180830145902.27376-2-cohuck@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Function comments reworded]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/util/qemu-error.c b/util/qemu-error.c
index a25d3b94c6..4ab428f7e4 100644
--- a/util/qemu-error.c
+++ b/util/qemu-error.c
@@ -310,3 +310,43 @@ void info_report(const char *fmt, ...)
     vreport(REPORT_TYPE_INFO, fmt, ap);
     va_end(ap);
 }
+
+/*
+ * Like error_report(), except print just once.
+ * If *printed is false, print the message, and flip *printed to true.
+ * Return whether the message was printed.
+ */
+bool error_report_once_cond(bool *printed, const char *fmt, ...)
+{
+    va_list ap;
+
+    assert(printed);
+    if (*printed) {
+        return false;
+    }
+    *printed = true;
+    va_start(ap, fmt);
+    vreport(REPORT_TYPE_ERROR, fmt, ap);
+    va_end(ap);
+    return true;
+}
+
+/*
+ * Like warn_report(), except print just once.
+ * If *printed is false, print the message, and flip *printed to true.
+ * Return whether the message was printed.
+ */
+bool warn_report_once_cond(bool *printed, const char *fmt, ...)
+{
+    va_list ap;
+
+    assert(printed);
+    if (*printed) {
+        return false;
+    }
+    *printed = true;
+    va_start(ap, fmt);
+    vreport(REPORT_TYPE_WARNING, fmt, ap);
+    va_end(ap);
+    return true;
+}