From: Steven Smith <ssmith@weybridge.uk.xensource.com>
Date: Fri, 2 Oct 2009 11:58:57 +0000 (+0100)
Subject: It turns out that Windows occasionally generates packets in which the
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=8347bd9dd052bff6a2d117d87b57ecbc362e9577;p=people%2Fssmith%2Fnc2-2.6.27.git

It turns out that Windows occasionally generates packets in which the
IP and TCP headers are in different fragments.  Make sure that the
backends can handle this.
---

diff --git a/drivers/xen/netback/xenbus.c b/drivers/xen/netback/xenbus.c
index 31cef720..b5099d6c 100644
--- a/drivers/xen/netback/xenbus.c
+++ b/drivers/xen/netback/xenbus.c
@@ -112,6 +112,16 @@ static int netback_probe(struct xenbus_device *dev,
 			goto abort_transaction;
 		}
 
+		/* We can cope with transmit checksum offload packets
+		   in which the TCP and IP headers are in separate
+		   fragments. */
+		err = xenbus_printf(xbt, dev->nodename,
+				    "feature-tx-csum-split-header", "%d", 1);
+		if (err) {
+			message = "writing feature-tx-csum-split-header";
+			goto abort_transaction;
+		}
+
 		/*
 		 * We don't support rx-flip path (except old guests who don't
 		 * grok this feature flag).
diff --git a/net/core/dev.c b/net/core/dev.c
index 226bb6ba..f84eed15 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1753,6 +1753,18 @@ static struct netdev_queue *dev_pick_tx(struct net_device *dev,
 }
 
 #if defined(CONFIG_XEN) || defined(CONFIG_PARAVIRT_XEN)
+static int skb_pull_up_to(struct sk_buff *skb, void *ptr)
+{
+	if (ptr < (void *)skb_tail_pointer(skb))
+		return 1;
+	if (__pskb_pull_tail(skb,
+			     ptr - (void *)skb->data - skb_headlen(skb))) {
+		return 1;
+	} else {
+		return 0;
+	}
+}
+
 inline int skb_checksum_setup(struct sk_buff *skb)
 {
 	struct iphdr *iph;
@@ -1768,10 +1780,10 @@ inline int skb_checksum_setup(struct sk_buff *skb)
 		goto out;
 
 	iph = ip_hdr(skb);
-	th = skb_network_header(skb) + 4 * iph->ihl;
-	if (th >= skb_tail_pointer(skb))
+	if (!skb_pull_up_to(skb, iph + 1))
 		goto out;
 
+	th = skb_network_header(skb) + 4 * iph->ihl;
 	skb->csum_start = th - skb->head;
 	switch (iph->protocol) {
 	case IPPROTO_TCP:
@@ -1788,7 +1800,7 @@ inline int skb_checksum_setup(struct sk_buff *skb)
 		goto out;
 	}
 
-	if ((th + skb->csum_offset + 2) > skb_tail_pointer(skb))
+	if (!skb_pull_up_to(skb, th + skb->csum_offset + 2))
 		goto out;
 
 #ifdef CONFIG_XEN