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>

3 files changed, 48 insertions, 15 deletions

diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
index e96bbdc..9246729 100644
--- a/hw/vfio/ccw.c
+++ b/hw/vfio/ccw.c
@@ -37,24 +37,12 @@ typedef struct VFIOCCWDevice {
     bool warned_orb_pfch;
 } VFIOCCWDevice;
 
-static inline void warn_once(bool *warned, const char *fmt, ...)
-{
-    va_list ap;
-
-    if (!warned || *warned) {
-        return;
-    }
-    *warned = true;
-    va_start(ap, fmt);
-    warn_vreport(fmt, ap);
-    va_end(ap);
-}
-
 static inline void warn_once_pfch(VFIOCCWDevice *vcdev, SubchDev *sch,
                                   const char *msg)
 {
-    warn_once(&vcdev->warned_orb_pfch, "vfio-ccw (devno %x.%x.%04x): %s",
-              sch->cssid, sch->ssid, sch->devno, msg);
+    warn_report_once_cond(&vcdev->warned_orb_pfch,
+                          "vfio-ccw (devno %x.%x.%04x): %s",
+                          sch->cssid, sch->ssid, sch->devno, msg);
 }
 
 static void vfio_ccw_compute_needs_reset(VFIODevice *vdev)
diff --git a/include/qemu/error-report.h b/include/qemu/error-report.h
index 72fab2b..e415128 100644
--- a/include/qemu/error-report.h
+++ b/include/qemu/error-report.h
@@ -44,6 +44,11 @@ void error_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 void warn_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 void info_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 
+bool error_report_once_cond(bool *printed, const char *fmt, ...)
+    GCC_FMT_ATTR(2, 3);
+bool warn_report_once_cond(bool *printed, const char *fmt, ...)
+    GCC_FMT_ATTR(2, 3);
+
 /*
  * Similar to error_report(), except it prints the message just once.
  * Return true when it prints, false otherwise.
diff --git a/util/qemu-error.c b/util/qemu-error.c
index a25d3b9..4ab428f 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;
+}