Introduce dm_strncpy

Should be faster then strncpy - since we could avoid clearing 4KB pages
with each strncpy(...,PATH_MAX).
Also it's easy to check whether string fit - and eventually avoid
to continue working we incomplete string.

WHATS_NEW_DM

@@ -1,5 +1,6 @@
 Version 1.02.73 - 
 ====================================
+  Add dm_strncpy() function as a faster strncpy() replacement.
 
 Version 1.02.72 - 23rd February 2012
 ====================================

libdm/libdevmapper.h

@@ -1211,6 +1211,15 @@ void dm_unescape_colons_and_at_signs(char *src,
 				     char **substr_first_unquoted_colon,
 				     char **substr_first_unquoted_at_sign);
 
+/*
+ * Replacement for strncpy() function.
+ *
+ * Copies no more than n bytes from string pointed by src to the buffer
+ * pointed by dest and ensure string is finished with '\0'.
+ * Returns 0 if the whole string does not fit.
+ */
+int dm_strncpy(char *dest, const char *src, size_t n);
+
 /**************************
  * file/stream manipulation
  **************************/

libdm/libdm-string.c

@@ -410,3 +410,13 @@ void dm_unescape_colons_and_at_signs(char *src,
 		*substr_first_unquoted_at_sign = arr_substr_first_unquoted[1];
 }
 
+int dm_strncpy(char *dest, const char *src, size_t n)
+{
+	if (memccpy(dest, src, 0, n))
+		return 1;
+
+	if (n > 0)
+		dest[n - 1] = '\0';
+
+	return 0;
+}