shared: add nm_errno() and nm_utils_error_set_errno() helper

shared/nm-utils/nm-shared-utils.h

@@ -480,6 +480,19 @@ _nm_g_slice_free_fcn_define (16)
 
 /*****************************************************************************/
 
+static inline int
+nm_errno (int errsv)
+{
+	/* several API returns negative errno values as errors. Normalize
+	 * negative values to positive values.
+	 *
+	 * As a special case, map G_MININT to G_MAXINT. If you care about the
+	 * distinction, then check for G_MININT before. */
+	return errsv >= 0
+	       ? errsv
+	       : ((errsv == G_MININT) ? G_MAXINT : -errsv);
+}
+
 /**
  * NMUtilsError:
  * @NM_UTILS_ERROR_UNKNOWN: unknown or unclassified error
@@ -542,6 +555,14 @@ nm_utils_error_set_literal (GError **error, int error_code, const char *literal)
 #define nm_utils_error_set(error, error_code, ...) \
 	g_set_error ((error), NM_UTILS_ERROR, error_code, __VA_ARGS__)
 
+#define nm_utils_error_set_errno(error, errsv, fmt, ...) \
+	g_set_error ((error), \
+	             NM_UTILS_ERROR, \
+	             NM_UTILS_ERROR_UNKNOWN, \
+	             fmt, \
+	             ##__VA_ARGS__, \
+	             g_strerror (nm_errno (errsv)))
+
 /*****************************************************************************/
 
 gboolean nm_g_object_set_property (GObject *object,