xen: netif.h: add a new extra type for XDP

The patch adds a new extra type to be able to diffirentiate
between RX responses on xen-netfront side with the adjusted offset
required for XDP processing.

The offset value from a guest is passed via xenstore.

Signed-off-by: Denis Kirjanov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/xen/interface/io/netif.h

···
  */
 
 /*
+ * "xdp-headroom" is used to request that extra space is added
+ * for XDP processing.  The value is measured in bytes and passed by
+ * the frontend to be consistent between both ends.
+ * If the value is greater than zero that means that
+ * an RX response is going to be passed to an XDP program for processing.
+ * XEN_NETIF_MAX_XDP_HEADROOM defines the maximum headroom offset in bytes
+ *
+ * "feature-xdp-headroom" is set to "1" by the netback side like other features
+ * so a guest can check if an XDP program can be processed.
+ */
+#define XEN_NETIF_MAX_XDP_HEADROOM 0x7FFF
+
+/*
  * Control ring
  * ============
  *
···
 #define XEN_NETIF_EXTRA_TYPE_MCAST_ADD (2)	/* u.mcast */
 #define XEN_NETIF_EXTRA_TYPE_MCAST_DEL (3)	/* u.mcast */
 #define XEN_NETIF_EXTRA_TYPE_HASH      (4)	/* u.hash */
-#define XEN_NETIF_EXTRA_TYPE_MAX       (5)
+#define XEN_NETIF_EXTRA_TYPE_XDP       (5)	/* u.xdp */
+#define XEN_NETIF_EXTRA_TYPE_MAX       (6)
 
 /* xen_netif_extra_info_t flags. */
 #define _XEN_NETIF_EXTRA_FLAG_MORE (0)
···
 			uint8_t algorithm;
 			uint8_t value[4];
 		} hash;
+		struct {
+			uint16_t headroom;
+			uint16_t pad[2];
+		} xdp;
 		uint16_t pad[3];
 	} u;
 };