[NET] front: Added feature-rx-notify

This patch adds support to the frontend for notifying the backend whenever
the rx ring is refilled.  This is required in order for the backend to
get a tx queue.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Modified to only send notification if req_event index is set
appropriately.

Signed-off-by: Keir Fraser <keir@xensource.com>

linux-2.6-xen-sparse/drivers/xen/netfront/netfront.c

@@ -326,6 +326,12 @@ again:
 		goto abort_transaction;
 	}
 
+	err = xenbus_printf(xbt, dev->nodename, "feature-rx-notify", "%d", 1);
+	if (err) {
+		message = "writing feature-rx-notify";
+		goto abort_transaction;
+	}
+
 	err = xenbus_transaction_end(xbt, 0);
 	if (err) {
 		if (err == -EAGAIN)
@@ -569,7 +575,7 @@ static void network_alloc_rx_buffers(struct net_device *dev)
 	unsigned short id;
 	struct netfront_info *np = netdev_priv(dev);
 	struct sk_buff *skb;
-	int i, batch_target;
+	int i, batch_target, notify;
 	RING_IDX req_prod = np->rx.req_prod_pvt;
 	struct xen_memory_reservation reservation;
 	grant_ref_t ref;
@@ -682,7 +688,9 @@ static void network_alloc_rx_buffers(struct net_device *dev)
 	/* Above is a suitable barrier to ensure backend will see requests. */
 	np->rx.req_prod_pvt = req_prod + i;
  push:
-	RING_PUSH_REQUESTS(&np->rx);
+	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&np->rx, notify);
+	if (notify)
+		notify_remote_via_irq(np->irq);
 }
 
 static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,

xen/include/public/io/netif.h

@@ -13,10 +13,11 @@
 #include "../grant_table.h"
 
 /*
- * Note that there is *never* any need to notify the backend when
- * enqueuing receive requests (struct netif_rx_request). Notifications
- * after enqueuing any other type of message should be conditional on
+ * Notifications after enqueuing any type of message should be conditional on
  * the appropriate req_event or rsp_event field in the shared ring.
+ * If the client sends notification for rx requests then it should specify
+ * feature 'feature-rx-notify' via xenbus. Otherwise the backend will assume
+ * that it cannot safely queue packets (as it may not be kicked to send them).
  */
 
 /*