X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=DESIGN;h=b06751f1573588eb7ca4193e78941cbf61d512bf;hb=fd94a42c43ff4a0e57a44bdc9ded1b7e1e63faaa;hp=a3a62b2eeb7f29c8ec4833d128621d28de39186a;hpb=4550b6475456b7b2e44ab464434f03aacdb9f33d;p=openvswitch

diff --git a/DESIGN b/DESIGN
index a3a62b2e..b06751f1 100644
--- a/DESIGN
+++ b/DESIGN
@@ -612,6 +612,39 @@ The following are explicitly *not* supported by in-band control:
      gateway.
 
 
+Action Reproduction
+===================
+
+It seems likely that many controllers, at least at startup, use the
+OpenFlow "flow statistics" request to obtain existing flows, then
+compare the flows' actions against the actions that they expect to
+find.  Before version 1.8.0, Open vSwitch always returned exact,
+byte-for-byte copies of the actions that had been added to the flow
+table.  The current version of Open vSwitch does not always do this in
+some exceptional cases.  This section lists the exceptions that
+controller authors must keep in mind if they compare actual actions
+against desired actions in a bytewise fashion:
+
+        - Open vSwitch zeros padding bytes in action structures,
+          regardless of their values when the flows were added.
+
+        - Open vSwitch "normalizes" the instructions in OpenFlow 1.1
+          (and later) in the following way:
+
+              * OVS sorts the instructions into the following order:
+                Apply-Actions, Clear-Actions, Write-Actions,
+                Write-Metadata, Goto-Table.
+
+              * OVS drops Apply-Actions instructions that have empty
+                action lists.
+
+              * OVS drops Write-Actions instructions that have empty
+                action sets.
+
+Please report other discrepancies, if you notice any, so that we can
+fix or document them.
+
+
 Suggestions
 ===========