ofp-util: Make ofputil_encode_set_protocol() able to return failure.

[openvswitch] / lib / ofp-util.c

diff --git a/lib/ofp-util.c b/lib/ofp-util.c
index 6ff9df894b72564f15693982d00a38aef96250e3..ad3fb369219fe8f666219719be1ef1fa40f4d9a4 100644 (file)
--- a/lib/ofp-util.c
+++ b/lib/ofp-util.c
@@ -1201,15 +1201,25 @@ ofputil_encode_hello(uint32_t allowed_versions)
  * connection if the switch processes the returned message correctly.  (If
  * '*next != want' then the caller will have to iterate.)
  *
- * If 'current == want', returns NULL and stores 'current' in '*next'. */
+ * If 'current == want', or if it is not possible to transition from 'current'
+ * to 'want' (because, for example, 'current' and 'want' use different OpenFlow
+ * protocol versions), returns NULL and stores 'current' in '*next'. */
 struct ofpbuf *
 ofputil_encode_set_protocol(enum ofputil_protocol current,
                             enum ofputil_protocol want,
                             enum ofputil_protocol *next)
 {
+    enum ofp_version cur_version, want_version;
     enum ofputil_protocol cur_base, want_base;
     bool cur_tid, want_tid;
 
+    cur_version = ofputil_protocol_to_ofp_version(current);
+    want_version = ofputil_protocol_to_ofp_version(want);
+    if (cur_version != want_version) {
+        *next = current;
+        return NULL;
+    }
+
     cur_base = ofputil_protocol_to_base(current);
     want_base = ofputil_protocol_to_base(want);
     if (cur_base != want_base) {