openvswitch: Avoid assigning a NULL pointer to flow actions.

Flow SET can accept an empty set of actions, with the intended
semantics of leaving existing actions unmodified.  This seems to have
been brokin after OVS 1.7, as we have assigned the flow's actions
pointer to NULL in this case, but we never check for the NULL pointer
later on.  This patch restores the intended behavior and documents it
in the include/linux/openvswitch.h.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
index 970553cbbc8e..0b979ee4bfc0 100644
--- a/include/uapi/linux/openvswitch.h
+++ b/include/uapi/linux/openvswitch.h
@@ -395,7 +395,9 @@ struct ovs_key_nd {
  * @OVS_FLOW_ATTR_ACTIONS: Nested %OVS_ACTION_ATTR_* attributes specifying
  * the actions to take for packets that match the key.  Always present in
  * notifications.  Required for %OVS_FLOW_CMD_NEW requests, optional for
- * %OVS_FLOW_CMD_SET requests.
+ * %OVS_FLOW_CMD_SET requests.  An %OVS_FLOW_CMD_SET without
+ * %OVS_FLOW_ATTR_ACTIONS will not modify the actions.  To clear the actions,
+ * an %OVS_FLOW_ATTR_ACTIONS without any nested attributes must be given.
  * @OVS_FLOW_ATTR_STATS: &struct ovs_flow_stats giving statistics for this
  * flow.  Present in notifications if the stats would be nonzero.  Ignored in
  * requests.