diff --git a/tools/libs/util/libxlu_cfg.c b/tools/libs/util/libxlu_cfg.c
index 874f5abfb9..b2947cbfc9 100644
--- a/tools/libs/util/libxlu_cfg.c
+++ b/tools/libs/util/libxlu_cfg.c
@@ -18,12 +18,19 @@
 #define _GNU_SOURCE
 
 #include <limits.h>
+#include <stdarg.h>
 
 #include "libxlu_internal.h"
 #include "libxlu_cfg_y.h"
 #include "libxlu_cfg_l.h"
 #include "libxlu_cfg_i.h"
 
+struct XLU_Config {
+    XLU_ConfigSetting *settings;
+    FILE *report;
+    char *config_source;
+};
+
 XLU_Config *xlu_cfg_init(FILE *report, const char *report_source) {
     XLU_Config *cfg;
 
@@ -703,6 +710,24 @@ void xlu__cfg_yyerror(YYLTYPE *loc, CfgParseContext *ctx, char const *msg) {
     if (!ctx->err) ctx->err= EINVAL;
 }
 
+int xlu_cfg_printf(XLU_Config *cfg, const char *format, ...)
+{
+	va_list args;
+	int ret;
+
+	if (!cfg || !cfg->report)
+		return EFAULT;
+
+	fwrite(cfg->config_source, 1, strlen(cfg->config_source), cfg->report);
+	fwrite(": ", 2, 1, cfg->report);
+
+	va_start(args, format);
+	ret = vfprintf(cfg->report, format, args);
+	va_end(args);
+
+	return ret;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/tools/libs/util/libxlu_disk.c b/tools/libs/util/libxlu_disk.c
index 1de16a6a06..a4d08ab7e9 100644
--- a/tools/libs/util/libxlu_disk.c
+++ b/tools/libs/util/libxlu_disk.c
@@ -5,13 +5,10 @@
 
 void xlu__disk_err(DiskParseContext *dpc, const char *erroneous,
                    const char *message) {
-    fprintf(dpc->cfg->report,
-            "%s: config parsing error in disk specification: %s"
-            "%s%s%s"
-            " in `%s'\n",
-            dpc->cfg->config_source, message,
-            erroneous?": near `":"", erroneous?erroneous:"", erroneous?"'":"",
-            dpc->spec);
+    xlu_cfg_printf(dpc->cfg,
+            "config parsing error in disk specification: %s%s%s%s in `%s'\n",
+            message, erroneous?": near `":"", erroneous?erroneous:"",
+            erroneous?"'":"", dpc->spec);
     if (!dpc->err) dpc->err= EINVAL;
 }
 
@@ -29,8 +26,7 @@ static int dpc_prep(DiskParseContext *dpc, const char *spec) {
     return 0;
 
  fail:
-    fprintf(dpc->cfg->report, "cannot init disk scanner: %s\n",
-            strerror(errno));
+    xlu_cfg_printf(dpc->cfg, "cannot init disk scanner: %s\n", strerror(errno));
     return e;
 }
 
diff --git a/tools/libs/util/libxlu_internal.h b/tools/libs/util/libxlu_internal.h
index 1f7559ecd9..2ef5eb7f5e 100644
--- a/tools/libs/util/libxlu_internal.h
+++ b/tools/libs/util/libxlu_internal.h
@@ -57,12 +57,6 @@ typedef struct XLU_ConfigSetting { /* transparent */
     int lineno;
 } XLU_ConfigSetting;
 
-struct XLU_Config {
-    XLU_ConfigSetting *settings;
-    FILE *report;
-    char *config_source;
-};
-
 typedef struct {
     XLU_Config *cfg;
     int err, lexerrlineno, likely_python;
@@ -73,6 +67,9 @@ typedef struct {
 #define STRINGIFY(x) #x
 #define TOSTRING(x) STRINGIFY(x)
 
+extern int xlu_cfg_printf(XLU_Config *cfg, const char *format, ...)
+    __attribute__((__format__ (__printf__, 2, 3)));
+
 #endif /*LIBXLU_INTERNAL_H*/
 
 /*
diff --git a/tools/libs/util/libxlu_pci.c b/tools/libs/util/libxlu_pci.c
index 294482c6d7..d6abbc1c1f 100644
--- a/tools/libs/util/libxlu_pci.c
+++ b/tools/libs/util/libxlu_pci.c
@@ -5,8 +5,7 @@
 #include "libxlu_internal.h"
 
 
-#define XLU__PCI_ERR(_c, _x, _a...) \
-    if((_c) && (_c)->report) fprintf((_c)->report, _x, ##_a)
+#define XLU__PCI_ERR(_c, _x, _a...) xlu_cfg_printf((_c), _x, ##_a)
 
 static int parse_bdf(libxl_device_pci *pci, const char *str, const char **endp)
 {
diff --git a/tools/libs/util/libxlu_vif.c b/tools/libs/util/libxlu_vif.c
index ccf0cbdf57..93c449e213 100644
--- a/tools/libs/util/libxlu_vif.c
+++ b/tools/libs/util/libxlu_vif.c
@@ -6,9 +6,7 @@ static const char *vif_bytes_per_sec_re = "^[0-9]+[GMK]?[Bb]/s$";
 static const char *vif_internal_usec_re = "^[0-9]+[mu]?s?$";
 
 static void xlu__vif_err(XLU_Config *cfg, const char *msg, const char *rate) {
-    fprintf(cfg->report,
-            "%s: config parsing error in vif: %s in `%s'\n",
-            cfg->config_source, msg, rate);
+    xlu_cfg_printf(cfg, "config parsing error in vif: %s in `%s'\n", msg, rate);
 }
 
 static int vif_parse_rate_bytes_per_sec(XLU_Config *cfg, const char *bytes,
