ofp-actions: Document that learn(limit=0) is no limit.

The documentation was unclear that specifying a limit of 0 is the same
as specifying no limit. Controllers that wish to set a learn limit so
that no more than 0 flows are learned may omit the learn action.

Signed-off-by: Joe Stringer <joe@ovn.org>
Acked-by: Jarno Rajahalme <jarno@ovn.org>

include/openvswitch/ofp-actions.h

@@ -762,7 +762,7 @@ struct ofpact_learn {
         uint16_t fin_idle_timeout; /* Idle timeout after FIN, if nonzero. */
         uint16_t fin_hard_timeout; /* Hard timeout after FIN, if nonzero. */
         /* If the number of flows on 'table_id' with 'cookie' exceeds this,
-         * the action will not add a new flow. */
+         * the action will not add a new flow. 0 indicates unlimited. */
         uint32_t limit;
         /* Used only if 'flags' has NX_LEARN_F_WRITE_RESULT.  If the execution
          * failed to install a new flow because 'limit' is exceeded,

lib/ofp-actions.c

@@ -4328,7 +4328,8 @@ OFP_ASSERT(sizeof(struct nx_action_learn) == 32);
 
 struct nx_action_learn2 {
     struct nx_action_learn up;  /* The wire format includes nx_action_learn. */
-    ovs_be32 limit;             /* Maximum number of learned flows. */
+    ovs_be32 limit;             /* Maximum number of learned flows.
+                                 * 0 indicates unlimited. */
 
     /* Where to store the result. */
     ovs_be16 result_dst_ofs;    /* Starting bit offset in destination. */

utilities/ovs-ofctl.8.in

@@ -1466,7 +1466,7 @@ This flag was added in Open vSwitch 2.4.
 .IP \fBlimit=\fInumber\fR
 If the number of flows in table \fBtable\fR with cookie id \fBcookie\fR exceeds
 \fInumber\fR, a new flow will not be learned by this action.  By default
-there's no limit.
+there's no limit. limit=0 is a long-hand for no limit.
 .
 .IP
 This flag was added in Open vSwitch 2.8.