util/error: Introduce warn_report_err_once()

Depending on the configuration of the host and VM, a passthrough
device may generate recurring DMA mapping errors at runtime. In such
cases, reporting the issue once is sufficient.

We have already the warn/error_report_once() routines taking a format
and arguments. Using the same design pattern, add a new warning
variant taking an 'Error *' parameter.

Cc: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250206131438.1505542-2-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

include/qapi/error.h

@@ -466,6 +466,18 @@ void warn_reportf_err(Error *err, const char *fmt, ...)
 void error_reportf_err(Error *err, const char *fmt, ...)
     G_GNUC_PRINTF(2, 3);
 
+/*
+ * Similar to warn_report_err(), except it prints the message just once.
+ * Return true when it prints, false otherwise.
+ */
+bool warn_report_err_once_cond(bool *printed, Error *err);
+
+#define warn_report_err_once(err)                           \
+    ({                                                      \
+        static bool print_once_;                            \
+        warn_report_err_once_cond(&print_once_, err);       \
+    })
+
 /*
  * Just like error_setg(), except you get to specify the error class.
  * Note: use of error classes other than ERROR_CLASS_GENERIC_ERROR is

util/error.c

@@ -247,6 +247,17 @@ void warn_report_err(Error *err)
     error_free(err);
 }
 
+bool warn_report_err_once_cond(bool *printed, Error *err)
+{
+    if (*printed) {
+        error_free(err);
+        return false;
+    }
+    *printed = true;
+    warn_report_err(err);
+    return true;
+}
+
 void error_reportf_err(Error *err, const char *fmt, ...)
 {
     va_list ap;