xen networking: add XDP offset adjustment to xen-netback

the patch basically adds the offset adjustment and netfront
state reading to make XDP work on netfront side.
Reviewed-by: Paul Durrant <paul@xen.org>
Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/common.h

@@ -281,6 +281,9 @@ struct xenvif {
 	u8 ipv6_csum:1;
 	u8 multicast_control:1;
 
+	/* headroom requested by xen-netfront */
+	u16 xdp_headroom;
+
 	/* Is this interface disabled? True when backend discovers
 	 * frontend is rogue.
 	 */
@@ -395,6 +398,7 @@ static inline pending_ring_idx_t nr_pending_reqs(struct xenvif_queue *queue)
 irqreturn_t xenvif_interrupt(int irq, void *dev_id);
 
 extern bool separate_tx_rx_irq;
+extern bool provides_xdp_headroom;
 
 extern unsigned int rx_drain_timeout_msecs;
 extern unsigned int rx_stall_timeout_msecs;

drivers/net/xen-netback/interface.c

@@ -483,6 +483,8 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
 	vif->queues = NULL;
 	vif->num_queues = 0;
 
+	vif->xdp_headroom = 0;
+
 	spin_lock_init(&vif->lock);
 	INIT_LIST_HEAD(&vif->fe_mcast_addr);
 

drivers/net/xen-netback/netback.c

@@ -96,6 +96,13 @@ unsigned int xenvif_hash_cache_size = XENVIF_HASH_CACHE_SIZE_DEFAULT;
 module_param_named(hash_cache_size, xenvif_hash_cache_size, uint, 0644);
 MODULE_PARM_DESC(hash_cache_size, "Number of flows in the hash cache");
 
+/* The module parameter tells that we have to put data
+ * for xen-netfront with the XDP_PACKET_HEADROOM offset
+ * needed for XDP processing
+ */
+bool provides_xdp_headroom = true;
+module_param(provides_xdp_headroom, bool, 0644);
+
 static void xenvif_idx_release(struct xenvif_queue *queue, u16 pending_idx,
 			       u8 status);
 

drivers/net/xen-netback/rx.c

@@ -258,6 +258,19 @@ static void xenvif_rx_next_skb(struct xenvif_queue *queue,
 		pkt->extra_count++;
 	}
 
+	if (queue->vif->xdp_headroom) {
+		struct xen_netif_extra_info *extra;
+
+		extra = &pkt->extras[XEN_NETIF_EXTRA_TYPE_XDP - 1];
+
+		memset(extra, 0, sizeof(struct xen_netif_extra_info));
+		extra->u.xdp.headroom = queue->vif->xdp_headroom;
+		extra->type = XEN_NETIF_EXTRA_TYPE_XDP;
+		extra->flags = 0;
+
+		pkt->extra_count++;
+	}
+
 	if (skb->sw_hash) {
 		struct xen_netif_extra_info *extra;
 
@@ -356,7 +369,7 @@ static void xenvif_rx_data_slot(struct xenvif_queue *queue,
 				struct xen_netif_rx_request *req,
 				struct xen_netif_rx_response *rsp)
 {
-	unsigned int offset = 0;
+	unsigned int offset = queue->vif->xdp_headroom;
 	unsigned int flags;
 
 	do {

drivers/net/xen-netback/xenbus.c

@@ -393,6 +393,24 @@ static void set_backend_state(struct backend_info *be,
 	}
 }
 
+static void read_xenbus_frontend_xdp(struct backend_info *be,
+				      struct xenbus_device *dev)
+{
+	struct xenvif *vif = be->vif;
+	u16 headroom;
+	int err;
+
+	err = xenbus_scanf(XBT_NIL, dev->otherend,
+			   "xdp-headroom", "%hu", &headroom);
+	if (err != 1) {
+		vif->xdp_headroom = 0;
+		return;
+	}
+	if (headroom > XEN_NETIF_MAX_XDP_HEADROOM)
+		headroom = XEN_NETIF_MAX_XDP_HEADROOM;
+	vif->xdp_headroom = headroom;
+}
+
 /**
  * Callback received when the frontend's state changes.
  */
@@ -417,6 +435,11 @@ static void frontend_changed(struct xenbus_device *dev,
 		set_backend_state(be, XenbusStateConnected);
 		break;
 
+	case XenbusStateReconfiguring:
+		read_xenbus_frontend_xdp(be, dev);
+		xenbus_switch_state(dev, XenbusStateReconfigured);
+		break;
+
 	case XenbusStateClosing:
 		set_backend_state(be, XenbusStateClosing);
 		break;
@@ -947,6 +970,8 @@ static int read_xenbus_vif_flags(struct backend_info *be)
 	vif->ipv6_csum = !!xenbus_read_unsigned(dev->otherend,
 						"feature-ipv6-csum-offload", 0);
 
+	read_xenbus_frontend_xdp(be, dev);
+
 	return 0;
 }
 
@@ -1036,6 +1061,15 @@ static int netback_probe(struct xenbus_device *dev,
 			goto abort_transaction;
 		}
 
+		/* we can adjust a headroom for netfront XDP processing */
+		err = xenbus_printf(xbt, dev->nodename,
+				    "feature-xdp-headroom", "%d",
+				    provides_xdp_headroom);
+		if (err) {
+			message = "writing feature-xdp-headroom";
+			goto abort_transaction;
+		}
+
 		/* We don't support rx-flip path (except old guests who
 		 * don't grok this feature flag).
 		 */