[PATCH] Add a new style of passing GSO packets to frontends.

[Paul Durrant <paul.durrant@citrix.com>]

feature-gso-tcpv4-prefix uses precedes the packet data passed to
the frontend with a ring entry that contains the necessary
metadata. This style of GSO passing is required for Citrix
Windows PV Drivers.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
---
 drivers/xen/netback/common.h     |    3 +-
 drivers/xen/netback/netback.c    |   43 ++++++++++++++++++++++++++++++++++---
 drivers/xen/netback/xenbus.c     |   17 +++++++++++---
 include/xen/interface/io/netif.h |    4 +++
 4 files changed, 58 insertions(+), 9 deletions(-)

diff --git a/drivers/xen/netback/common.h b/drivers/xen/netback/common.h
index 857778c..1cbc4ff 100644
--- a/drivers/xen/netback/common.h
+++ b/drivers/xen/netback/common.h
@@ -82,7 +82,8 @@ struct xen_netif {
 	int smart_poll;
 
 	/* Internal feature information. */
-	u8 can_queue:1;	/* can queue packets for receiver? */
+	u8 can_queue:1;	    /* can queue packets for receiver? */
+	u8 gso_prefix:1;    /* use a prefix segment for GSO information */
 
 	/* Allow netif_be_start_xmit() to peek ahead in the rx request
 	 * ring.  This is a prediction of what rx_req_cons will be once
diff --git a/drivers/xen/netback/netback.c b/drivers/xen/netback/netback.c
index c8f5c1b..93f0686 100644
--- a/drivers/xen/netback/netback.c
+++ b/drivers/xen/netback/netback.c
@@ -313,8 +313,12 @@ int netif_be_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	netbk = &xen_netbk[netif->group];
 
+	/* Drop the packet if the netif is not up or there is no carrier. */
+	if (unlikely(!netif_schedulable(netif)))
+		goto drop;
+
 	/* Drop the packet if the target domain has no receive buffers. */
-	if (unlikely(!netif_schedulable(netif) || netbk_queue_full(netif)))
+	if (unlikely(netbk_queue_full(netif)))
 		goto drop;
 
 	/*
@@ -432,6 +436,7 @@ static void netbk_gop_frag_copy(struct xen_netif *netif,
 			/* Overflowed this request, go to the next one */
 			req = RING_GET_REQUEST(&netif->rx, netif->rx.req_cons++);
 			meta = npo->meta + npo->meta_prod++;
+			meta->gso_size = 0;
 			meta->size = 0;
 			meta->id = req->id;
 			npo->copy_off = 0;
@@ -492,9 +497,23 @@ static int netbk_gop_skb(struct sk_buff *skb,
 
 	old_meta_prod = npo->meta_prod;
 
+	/* Set up a GSO prefix descriptor, if necessary */
+	if (skb_shinfo(skb)->gso_size && netif->gso_prefix) {
+		req = RING_GET_REQUEST(&netif->rx, netif->rx.req_cons++);
+		meta = npo->meta + npo->meta_prod++;
+		meta->gso_size = skb_shinfo(skb)->gso_size;
+		meta->size = 0;
+		meta->id = req->id;
+	}
+
 	req = RING_GET_REQUEST(&netif->rx, netif->rx.req_cons++);
 	meta = npo->meta + npo->meta_prod++;
-	meta->gso_size = skb_shinfo(skb)->gso_size;
+
+	if (!netif->gso_prefix)
+		meta->gso_size = skb_shinfo(skb)->gso_size;
+	else
+		meta->gso_size = 0;
+
 	meta->size = 0;
 	meta->id = req->id;
 	npo->copy_off = 0;
@@ -506,7 +525,7 @@ static int netbk_gop_skb(struct sk_buff *skb,
 			    offset_in_page(skb->data), 1);
 
 	/* Leave a gap for the GSO descriptor. */
-	if (skb_shinfo(skb)->gso_size)
+	if (skb_shinfo(skb)->gso_size && !netif->gso_prefix)
 		netif->rx.req_cons++;
 
 	for (i = 0; i < nr_frags; i++) {
@@ -623,6 +642,21 @@ static void net_rx_action(unsigned long data)
 
 		netif = netdev_priv(skb->dev);
 
+		if (netbk->meta[npo.meta_cons].gso_size && netif->gso_prefix) {
+			resp = RING_GET_RESPONSE(&netif->rx,
+						netif->rx.rsp_prod_pvt++);
+
+			resp->flags = NETRXF_gso_prefix | NETRXF_more_data;
+
+			resp->offset = netbk->meta[npo.meta_cons].gso_size;
+			resp->id = netbk->meta[npo.meta_cons].id;
+			resp->status = sco->meta_slots_used;
+
+			npo.meta_cons++;
+			sco->meta_slots_used--;
+		}
+
+
 		netif->stats.tx_bytes += skb->len;
 		netif->stats.tx_packets++;
 
@@ -633,6 +667,7 @@ static void net_rx_action(unsigned long data)
 			flags = 0;
 		else
 			flags = NETRXF_more_data;
+
 		if (skb->ip_summed == CHECKSUM_PARTIAL) /* local packet? */
 			flags |= NETRXF_csum_blank | NETRXF_data_validated;
 		else if (skb->ip_summed == CHECKSUM_UNNECESSARY)
@@ -645,7 +680,7 @@ static void net_rx_action(unsigned long data)
 					netbk->meta[npo.meta_cons].size,
 					flags);
 
-		if (netbk->meta[npo.meta_cons].gso_size) {
+		if (netbk->meta[npo.meta_cons].gso_size && !netif->gso_prefix) {
 			struct xen_netif_extra_info *gso =
 				(struct xen_netif_extra_info *)
 				RING_GET_RESPONSE(&netif->rx,
diff --git a/drivers/xen/netback/xenbus.c b/drivers/xen/netback/xenbus.c
index ba7b1de..74c035b 100644
--- a/drivers/xen/netback/xenbus.c
+++ b/drivers/xen/netback/xenbus.c
@@ -465,16 +465,25 @@ static int connect_rings(struct backend_info *be)
 			be->netif->dev->mtu = ETH_DATA_LEN;
 	}
 
-	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4", "%d",
-			 &val) < 0)
+	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4",
+			"%d", &val) < 0)
 		val = 0;
 	if (val) {
 		be->netif->features |= NETIF_F_TSO;
 		be->netif->dev->features |= NETIF_F_TSO;
 	}
 
+	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-gso-tcpv4-prefix",
+			"%d", &val) < 0)
+		val = 0;
+	if (val) {
+		be->netif->features |= NETIF_F_TSO;
+		be->netif->dev->features |= NETIF_F_TSO;
+		be->netif->gso_prefix = 1;
+	}
+
 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-no-csum-offload",
-			 "%d", &val) < 0)
+			"%d", &val) < 0)
 		val = 0;
 	if (val) {
 		be->netif->features &= ~NETIF_F_IP_CSUM;
@@ -482,7 +491,7 @@ static int connect_rings(struct backend_info *be)
 	}
 
 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-smart-poll",
-			 "%d", &val) < 0)
+			"%d", &val) < 0)
 		val = 0;
 	if (val)
 		be->netif->smart_poll = 1;
diff --git a/include/xen/interface/io/netif.h b/include/xen/interface/io/netif.h
index 518481c..8309344 100644
--- a/include/xen/interface/io/netif.h
+++ b/include/xen/interface/io/netif.h
@@ -131,6 +131,10 @@ struct xen_netif_rx_request {
 #define _NETRXF_extra_info     (3)
 #define  NETRXF_extra_info     (1U<<_NETRXF_extra_info)
 
+/* GSO Prefix descriptor. */
+#define _NETRXF_gso_prefix     (4)
+#define  NETRXF_gso_prefix     (1U<<_NETRXF_gso_prefix)
+
 struct xen_netif_rx_response {
     uint16_t id;
     uint16_t offset;       /* Offset in page of start of received packet  */
-- 
1.5.6.5