conntrack: Remove nat_conn introducing key directionality.

The patch avoids the extra allocation for nat_conn.
Currently, when doing NAT, the userspace conntrack will use an extra
conn for the two directions in a flow. However, each conn has actually
the two keys for both orig and rev directions. This patch introduces a
key_node[CT_DIRS] member as per Aaron's suggestion in the conn which
consists of a key, direction, and a cmap_node for hash lookup so
addressing the feedback received by the original patch [0].

With this adjustment, we also remove the assertion that connections in
the table are DEFAULT while updating connection state and/or removing
connections.

[0] https://patchwork.ozlabs.org/project/openvswitch/patch/20201129033255.64647-2-hepeng.0320@bytedance.com/

[Aaron resolved 2 conflicts in conntrack.c due to missing commits
 501f665 ("conntrack: Extract l4 information for SCTP.")
 a3848d9 ("conntrack: Show parent key if present.")]

Reported-by: Michael Plato <michael.plato@tu-berlin.de>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2022-September/052065.html
Signed-off-by: Peng He <hepeng.0320@bytedance.com>
Co-authored-by: Paolo Valerio <pvalerio@redhat.com>
Signed-off-by: Paolo Valerio <pvalerio@redhat.com>
Tested-by: Frode Nordahl <frode.nordahl@canonical.com>
Acked-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Aaron Conole <aconole@redhat.com>

lib/conntrack-private.h

@@ -49,6 +49,12 @@ struct ct_endpoint {
  * hashing in ct_endpoint_hash_add(). */
 BUILD_ASSERT_DECL(sizeof(struct ct_endpoint) == sizeof(union ct_addr) + 4);
 
+enum key_dir {
+    CT_DIR_FWD = 0,
+    CT_DIR_REV,
+    CT_DIRS,
+};
+
 /* Changes to this structure need to be reflected in conn_key_hash()
  * and conn_key_cmp(). */
 struct conn_key {
@@ -112,20 +118,18 @@ enum ct_timeout {
 
 #define N_EXP_LISTS 100
 
-enum OVS_PACKED_ENUM ct_conn_type {
-    CT_CONN_TYPE_DEFAULT,
-    CT_CONN_TYPE_UN_NAT,
+struct conn_key_node {
+    enum key_dir dir;
+    struct conn_key key;
+    struct cmap_node cm_node;
 };
 
 struct conn {
     /* Immutable data. */
-    struct conn_key key;
-    struct conn_key rev_key;
+    struct conn_key_node key_node[CT_DIRS];
     struct conn_key parent_key; /* Only used for orig_tuple support. */
-    struct cmap_node cm_node;
     uint16_t nat_action;
     char *alg;
-    struct conn *nat_conn; /* The NAT 'conn' context, if there is one. */
     atomic_flag reclaimed; /* False during the lifetime of the connection,
                             * True as soon as a thread has started freeing
                             * its memory. */
@@ -150,7 +154,6 @@ struct conn {
 
     /* Immutable data. */
     bool alg_related; /* True if alg data connection. */
-    enum ct_conn_type conn_type;
 
     uint32_t tp_id; /* Timeout policy ID. */
 };

lib/conntrack-tp.c

@@ -253,7 +253,8 @@ conn_update_expiration(struct conntrack *ct, struct conn *conn,
     }
     VLOG_DBG_RL(&rl, "Update timeout %s zone=%u with policy id=%d "
                 "val=%u sec.",
-                ct_timeout_str[tm], conn->key.zone, conn->tp_id, val);
+                ct_timeout_str[tm], conn->key_node[CT_DIR_FWD].key.zone,
+                conn->tp_id, val);
 
     atomic_store_relaxed(&conn->expiration, now + val * 1000);
 }
@@ -273,7 +274,8 @@ conn_init_expiration(struct conntrack *ct, struct conn *conn,
     }
 
     VLOG_DBG_RL(&rl, "Init timeout %s zone=%u with policy id=%d val=%u sec.",
-                ct_timeout_str[tm], conn->key.zone, conn->tp_id, val);
+                ct_timeout_str[tm], conn->key_node[CT_DIR_FWD].key.zone,
+                conn->tp_id, val);
 
     conn->expiration = now + val * 1000;
 }