ofproto: Limit OVS-assigned port numbers to 32767 and below.

A couple of controller vendors have mentioned to me that they would like to
have some part of the OpenFlow port number space reserved for the
controller to use.  This commit reserves 32768 and up (roughly the upper
half of the OF1.0 port range) to the controller.

Bug #18753.
Signed-off-by: Ben Pfaff <blp@nicira.com>

NEWS

@@ -6,6 +6,9 @@ Post-v2.0.0
      defaults.
    - OpenFlow:
      * The OpenFlow 1.1+ "Write-Actions" instruction is now supported.
+     * OVS limits the OpenFlow port numbers it assigns to port 32767 and
+       below, leaving port numbers above that range free for assignment
+       by the controller.
    - ovs-vswitchd.conf.db.5 man page will contain graphviz/dot
      diagram only if graphviz package was installed at the build time.
    - Support for Linux kernels up to 3.11

ofproto/ofproto.c

@@ -2004,9 +2004,13 @@ alloc_ofp_port(struct ofproto *ofproto, const char *netdev_name)
 
         /* Search for a free OpenFlow port number.  We try not to
          * immediately reuse them to prevent problems due to old
-         * flows. */
+         * flows.
+         *
+         * We limit the automatically assigned port numbers to the lower half
+         * of the port range, to reserve the upper half for assignment by
+         * controllers. */
         for (;;) {
-            if (++ofproto->alloc_port_no >= ofproto->max_ports) {
+            if (++ofproto->alloc_port_no >= MIN(ofproto->max_ports, 32768)) {
                 ofproto->alloc_port_no = 1;
             }
             last_used_at = ofport_get_usage(ofproto,

vswitchd/vswitch.xml

@@ -1254,33 +1254,54 @@
         address.</p>
       </column>
 
-      <column name="ofport">
+      <group title="OpenFlow Port Number">
-        <p>OpenFlow port number for this interface.  Unlike most columns, this
+	<p>
-        column's value should be set only by Open vSwitch itself.  Other
+	  When a client adds a new interface, Open vSwitch chooses an OpenFlow
-        clients should set this column to an empty set (the default) when
+	  port number for the new port.  If the client that adds the port fills
-        creating an <ref table="Interface"/>.</p>
+	  in <ref column="ofport_request"/>, then Open vSwitch tries to use its
-        <p>Open vSwitch populates this column when the port number becomes
+	  value as the OpenFlow port number.  Otherwise, or if the requested
-        known.  If the interface is successfully added,
+	  port number is already in use or cannot be used for another reason,
-        <ref column="ofport"/> will be set to a number between 1 and 65535
+	  Open vSwitch automatically assigns a free port number.  Regardless of
-        (generally either in the range 1 to 65279, inclusive, or 65534, the
+	  how the port number was obtained, Open vSwitch then reports in <ref
-        port number for the OpenFlow ``local port'').  If the interface
+	  column="ofport"/> the port number actually assigned.
-        cannot be added then Open vSwitch sets this column
+	</p>
-        to -1.</p>
-        <p>When <ref column="ofport_request"/> is not set, Open vSwitch picks
-        an appropriate value for this column and then tries to keep the value
-        constant across restarts.</p>
-      </column>
 
-      <column name="ofport_request">
+	<p>
-        <p>Requested OpenFlow port number for this interface.  The port
+	  Open vSwitch limits the port numbers that it automatically assigns to
-        number must be between 1 and 65279, inclusive.  Some datapaths
+	  the range 1 through 32,767, inclusive.  Controllers therefore have
-        cannot satisfy all requests for particular port numbers.  When
+	  free use of ports 32,768 and up.
-        this column is empty or the request cannot be fulfilled, the
+	</p>
-        system will choose a free port.  The <ref column="ofport"/>
+
-        column reports the assigned OpenFlow port number.</p>
+	<column name="ofport">
-        <p>The port number must be requested in the same transaction
+	  <p>
-        that creates the port.</p>
+	    OpenFlow port number for this interface.  Open vSwitch sets this
-      </column>
+	    column's value, so other clients should treat it as read-only.
+	  </p>
+	  <p>
+	    The OpenFlow ``local'' port (<code>OFPP_LOCAL</code>) is 65,534.
+	    The other valid port numbers are in the range 1 to 65,279,
+	    inclusive.  Value -1 indicates an error adding the interface.
+	  </p>
+	</column>
+
+	<column name="ofport_request"
+		type='{"type": "integer", "minInteger": 1, "maxInteger": 65279}'>
+	  <p>
+	    Requested OpenFlow port number for this interface.
+	  </p>
+
+	  <p>
+	    Open vSwitch currently assigns the OpenFlow port number for an
+	    interface once, when the client first adds the interface.  It does
+	    not change the port number later if the client sets or changes or
+	    clears <ref column="ofport_request"/>.  Therefore, to ensure that
+	    <ref column="ofport_request"/> takes effect, the client should set
+	    it in the same database transaction that creates the interface.
+	    (Future versions of Open vSwitch might honor changes to <ref
+	    column="ofport_request"/>.)
+	  </p>
+	</column>
+      </group>
     </group>
 
     <group title="System-Specific Details">