ixgbe: Don't priority tag control frames in DCB mode

Certain types of control packets (LLDP, LACP, etc.) are not supposed to have a
priority tag or vlan tag inserted.  Ixgbe driver is currently priority
tagging everything (if packet is not on a VLAN interface).

This patch modifies DCB mode, so that packets marked with skb priority
TC_PRIO_CONTROL are not priority tagged.  It also transmits these packets on
the highest priority traffic class.
Programs (like dcbd) can set the skb priority using a socket option.  Or, a tc
filter can be configured to set the priority value. Using the value
TC_PRIO_CONTROL (7) has the benefit that it is already defined in the kernel,
and the bonding LACP code already sets the skb->priority field to this value.
Signed-off-by: Lucy Liu <lucy.liu@intel.com>
Acked-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ixgbe/ixgbe_main.c

@@ -34,6 +34,7 @@
 #include <linux/in.h>
 #include <linux/ip.h>
 #include <linux/tcp.h>
+#include <linux/pkt_sched.h>
 #include <linux/ipv6.h>
 #include <net/checksum.h>
 #include <net/ip6_checksum.h>
@@ -5126,9 +5127,6 @@ static int ixgbe_xmit_frame(struct sk_buff *skb, struct net_device *netdev)
 	int count = 0;
 	unsigned int f;
 
-	r_idx = skb->queue_mapping;
-	tx_ring = &adapter->tx_ring[r_idx];
-
 	if (adapter->vlgrp && vlan_tx_tag_present(skb)) {
 		tx_flags |= vlan_tx_tag_get(skb);
 		if (adapter->flags & IXGBE_FLAG_DCB_ENABLED) {
@@ -5138,10 +5136,18 @@ static int ixgbe_xmit_frame(struct sk_buff *skb, struct net_device *netdev)
 		tx_flags <<= IXGBE_TX_FLAGS_VLAN_SHIFT;
 		tx_flags |= IXGBE_TX_FLAGS_VLAN;
 	} else if (adapter->flags & IXGBE_FLAG_DCB_ENABLED) {
+		if (skb->priority != TC_PRIO_CONTROL) {
 			tx_flags |= (skb->queue_mapping << 13);
 			tx_flags <<= IXGBE_TX_FLAGS_VLAN_SHIFT;
 			tx_flags |= IXGBE_TX_FLAGS_VLAN;
+		} else {
+			skb->queue_mapping =
+				adapter->ring_feature[RING_F_DCB].indices-1;
 		}
+	}
+
+	r_idx = skb->queue_mapping;
+	tx_ring = &adapter->tx_ring[r_idx];
 
 	if ((adapter->flags & IXGBE_FLAG_FCOE_ENABLED) &&
 	    (skb->protocol == htons(ETH_P_FCOE)))