[ovs-dev] [PATCH] ofp-flow: Improve error message when cookie cannot be set.

[Ben Pfaff]

The "cookie" value has two meanings in "ovs-ofctl add-flow", etc.  With
a mask, it indicates a match; without a mask, it indicates that the
cookie should be set.  In some case, the cookie cannot be set, which may
mean that the user meant to indicate a match.  The error message for this
case was poor; this improves it.

Suggested-by: "Yi Yang (杨燚)-云服务集团" <yangyi01 at inspur.com>
Signed-off-by: Ben Pfaff <blp at ovn.org>
---
 lib/ofp-flow.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/ofp-flow.c b/lib/ofp-flow.c
index c45afd204f80..ff0396845a4e 100644
--- a/lib/ofp-flow.c
+++ b/lib/ofp-flow.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2017 Nicira, Inc.
+ * Copyright (c) 2008-2017, 2019 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -1660,7 +1660,9 @@ parse_ofp_str__(struct ofputil_flow_mod *fm, int command, char *string,
                     /* No mask means that the cookie is being set. */
                     if (command != OFPFC_ADD && command != OFPFC_MODIFY
                         && command != OFPFC_MODIFY_STRICT) {
-                        return xstrdup("cannot set cookie");
+                        return xasprintf("cannot set cookie (to match on a "
+                                         "cookie, specify a mask, e.g. "
+                                         "cookie=%s/-1)", value);
                     }
                     error = str_to_be64(value, &fm->new_cookie);
                     fm->modify_cookie = true;
-- 
2.20.1