Add dm_snprintf

WHATS_NEW_DM

@@ -1,6 +1,6 @@
 Version 1.02.10 - 
 ==============================
-  Add dm_split_words() and dm_split_lvm_name() to libdevmapper.
+  Add dm_snprintf(), dm_split_words() and dm_split_lvm_name() to libdevmapper.
   Reorder mm bounds_check code to reduce window for a dmeventd race.
 
 Version 1.02.09 - 15 Aug 2006

libdm/.exported_symbols

@@ -111,3 +111,4 @@ dm_set_selinux_context
 dm_task_set_geometry
 dm_split_lvm_name
 dm_split_words
+dm_snprintf

libdm/libdevmapper.h

@@ -17,6 +17,7 @@
 #define LIB_DEVICE_MAPPER_H
 
 #include <inttypes.h>
+#include <stdarg.h>
 #include <sys/types.h>
 
 #ifdef linux
@@ -601,4 +602,9 @@ int dm_split_words(char *buffer, unsigned max,
 		   unsigned ignore_comments, /* Not implemented */
 		   char **argv);
 
+/* 
+ * Returns -1 if buffer too small
+ */
+int dm_snprintf(char *buf, size_t bufsize, const char *format, ...);
+
 #endif				/* LIB_DEVICE_MAPPER_H */

libdm/libdm-string.c

@@ -99,3 +99,25 @@ int dm_split_lvm_name(struct dm_pool *mem, const char *dmname,
 
 	return 1;
 }
+
+/*
+ * On error, up to glibc 2.0.6, snprintf returned -1 if buffer was too small;
+ * From glibc 2.1 it returns number of chars (excl. trailing null) that would 
+ * have been written had there been room.
+ *
+ * dm_snprintf reverts to the old behaviour.
+ */
+int dm_snprintf(char *buf, size_t bufsize, const char *format, ...)
+{
+	int n;
+	va_list ap;
+
+	va_start(ap, format);
+	n = vsnprintf(buf, bufsize, format, ap);
+	va_end(ap);
+
+	if (n < 0 || (n > bufsize - 1))
+		return -1;
+
+	return n;
+}