Suggested-by: Justin Pettit <jpet...@nicira.com>
Signed-off-by: Ben Pfaff <b...@nicira.com>
---
lib/ofp-actions.h | 26 +++++++++++++++++++++++++-
1 files changed, 25 insertions(+), 1 deletions(-)
diff --git a/lib/ofp-actions.h b/lib/ofp-actions.h
index 75ccc26..46e2d79 100644
--- a/lib/ofp-actions.h
+++ b/lib/ofp-actions.h
@@ -108,7 +108,31 @@ enum {
*
* Each action is a structure "struct ofpact_*" that begins with "struct
* ofpact", usually followed by other data that describes the action. Actions
- * are padded out to a multiple of OFPACT_ALIGNTO bytes in length. */
+ * are padded out to a multiple of OFPACT_ALIGNTO bytes in length.
+ *
+ * The 'compat' member is special:
+ *
+ * - Most "struct ofpact"s correspond to one particular kind of OpenFlow
+ * action, at least in a given OpenFlow version. For example,
+ * OFPACT_SET_VLAN_VID corresponds to OFPAT10_SET_VLAN_VID in OpenFlow
+ * 1.0.
+ *
+ * For such actions, the 'compat' member is not meaningful and generally
+ * should be zero.
+ *
+ * - A few "struct ofpact"s correspond to multiple OpenFlow actions. For
+ * example, OFPACT_SET_TUNNEL can be NXAST_SET_TUNNEL or
+ * NXAST_SET_TUNNEL64. In these cases, if the "struct ofpact" originated
+ * from OpenFlow, then we want to make sure that, if it gets translated
+ * back to OpenFlow later, it is translated back to the same action type.
+ * (Otherwise, we'd violate the promise made in DESIGN, in the "Action
+ * Reproduction" section.)
+ *
+ * For such actions, the 'compat' member should be the original action
+ * type. (If the action didn't originate from OpenFlow, then setting
+ * 'compat' to zero should be fine: code to translate the ofpact to
+ * OpenFlow must tolerate this case.)
+ */
struct ofpact {
enum ofpact_type type; /* OFPACT_*. */
enum ofputil_action_code compat; /* Original type when added, if any. */
--
1.7.2.5
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