ofproto-dpif-xlate: Add "always" mode to priority tags

Configure "if-nonzero" priority tags to retain the 802.1Q header
when the VLAN ID is zero, except both the VLAN ID and priority are zero.
Add a "always" configuration option to retain the 802.1Q header in such
frames as well.

Signed-off-by: Eli Britstein <elibr@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

NEWS

@@ -21,6 +21,8 @@ Post-v2.11.0
      * New "ovs-appctl dpctl/ipf-get-status" command for userspace datapath
        conntrack fragmentation support.
      * New action "check_pkt_len".
+     * Port configuration with "other-config:priority-tags" now has a mode
+       that retains the 802.1Q header even if VLAN and priority are both zero.
    - OVSDB:
      * OVSDB clients can now resynchronize with clustered servers much more
        quickly after a brief disconnection, saving bandwidth and CPU time.

ofproto/ofproto-dpif-xlate.c

@@ -549,7 +549,8 @@ static void xvlan_copy(struct xvlan *dst, const struct xvlan *src);
 static void xvlan_pop(struct xvlan *src);
 static void xvlan_push_uninit(struct xvlan *src);
 static void xvlan_extract(const struct flow *, struct xvlan *);
-static void xvlan_put(struct flow *, const struct xvlan *);
+static void xvlan_put(struct flow *, const struct xvlan *,
+                      enum port_priority_tags_mode);
 static void xvlan_input_translate(const struct xbundle *,
                                   const struct xvlan *in,
                                   struct xvlan *xvlan);
@@ -2270,13 +2271,15 @@ xvlan_extract(const struct flow *flow, struct xvlan *xvlan)
 
 /* Put VLAN information (headers) to flow */
 static void
-xvlan_put(struct flow *flow, const struct xvlan *xvlan)
+xvlan_put(struct flow *flow, const struct xvlan *xvlan,
+          enum port_priority_tags_mode use_priority_tags)
 {
     ovs_be16 tci;
     int i;
     for (i = 0; i < FLOW_MAX_VLAN_HEADERS; i++) {
         tci = htons(xvlan->v[i].vid | (xvlan->v[i].pcp & VLAN_PCP_MASK));
-        if (tci) {
+        if (tci || ((use_priority_tags == PORT_PRIORITY_TAGS_ALWAYS) &&
+            xvlan->v[i].tpid)) {
             tci |= htons(VLAN_CFI);
             flow->vlans[i].tpid = xvlan->v[i].tpid ?
                                   htons(xvlan->v[i].tpid) :
@@ -2450,7 +2453,7 @@ output_normal(struct xlate_ctx *ctx, const struct xbundle *out_xbundle,
     }
 
     memcpy(&old_vlans, &ctx->xin->flow.vlans, sizeof(old_vlans));
-    xvlan_put(&ctx->xin->flow, &out_xvlan);
+    xvlan_put(&ctx->xin->flow, &out_xvlan, out_xbundle->use_priority_tags);
 
     compose_output_action(ctx, xport->ofp_port, use_recirc ? &xr : NULL,
                           false, false);

ofproto/ofproto.h

@@ -420,6 +420,7 @@ enum port_vlan_mode {
 enum port_priority_tags_mode {
     PORT_PRIORITY_TAGS_NEVER = 0,
     PORT_PRIORITY_TAGS_IF_NONZERO,
+    PORT_PRIORITY_TAGS_ALWAYS,
 };
 
 /* The behaviour of the port regarding priority tags */

vswitchd/bridge.c

@@ -1026,6 +1026,8 @@ port_configure(struct port *port)
     const char *pt = smap_get_def(&cfg->other_config, "priority-tags", "");
     if (!strcmp(pt, "if-nonzero") || !strcmp(pt, "true")) {
         s.use_priority_tags = PORT_PRIORITY_TAGS_IF_NONZERO;
+    } else if (!strcmp(pt, "always")) {
+        s.use_priority_tags = PORT_PRIORITY_TAGS_ALWAYS;
     } else {
         s.use_priority_tags = PORT_PRIORITY_TAGS_NEVER;
     }

vswitchd/vswitch.xml

@@ -1877,7 +1877,7 @@
 
       <column name="other_config" key="priority-tags"
               type='{"type": "string",
-                     "enum": ["set", ["never", "if-nonzero"]]}'>
+                     "enum": ["set", ["never", "if-nonzero", "always"]]}'>
         <p>
           An 802.1Q header contains two important pieces of information: a VLAN
           ID and a priority.  A frame with a zero VLAN ID, called a
@@ -1894,8 +1894,10 @@
         </p>
 
         <p>
-          Regardless of this setting, Open vSwitch omits the 802.1Q header on
+          For <code>if-nonzero</code> Open vSwitch omits the 802.1Q header on
-          output if both the VLAN ID and priority would be zero.
+          output if both the VLAN ID and priority would be zero. Set to
+          <code>always</code> to retain the 802.1Q header in such frames as
+          well.
         </p>
 
         <p>