memory: Document the memory/show unixctl command.

[openvswitch] / DESIGN

diff --git a/DESIGN b/DESIGN
index f9345d16e45485131001248256a18fc176902eeb..b06751f1573588eb7ca4193e78941cbf61d512bf 100644 (file)
--- a/DESIGN
+++ b/DESIGN
@@ -17,8 +17,14 @@ given controller receives OpenFlow asynchronous messages.  This
 section describes how all of these features interact.
 
 First, a service controller never receives any asynchronous messages
-unless it explicitly configures a miss_send_len greater than zero with
-an OFPT_SET_CONFIG message.
+unless it changes its miss_send_len from the service controller
+default of zero in one of the following ways:
+
+    - Sending an OFPT_SET_CONFIG message with nonzero miss_send_len.
+
+    - Sending any NXT_SET_ASYNC_CONFIG message: as a side effect, this
+      message changes the miss_send_len to
+      OFP_DEFAULT_MISS_SEND_LEN (128) for service controllers.
 
 Second, OFPT_FLOW_REMOVED and NXT_FLOW_REMOVED messages are generated
 only if the flow that was removed had the OFPFF_SEND_FLOW_REM flag
@@ -606,6 +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
 ===========