From: ack@localhost.localdomain <ack@localhost.localdomain>
Date: Tue, 15 Aug 2006 14:48:31 +0000 (+0100)
Subject: Don't copy all incoming fragmented packets.
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~15710^2~105
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=7df96ad1456a1608cabebe2322418590b3949e09;p=xen.git

Don't copy all incoming fragmented packets.
Some drivers (ie the e1000) hand up packets with the header in
the main area and the data in a fragment. Unless there are
multiple references on any of the data, we don't need to
make a full copy of those packets.
Signed-off-by: Emmanuel Ackaouy <ack@xensource.com>
---

diff --git a/linux-2.6-xen-sparse/drivers/xen/netback/netback.c b/linux-2.6-xen-sparse/drivers/xen/netback/netback.c
index c7c4c3d752..8d8e71bca9 100644
--- a/linux-2.6-xen-sparse/drivers/xen/netback/netback.c
+++ b/linux-2.6-xen-sparse/drivers/xen/netback/netback.c
@@ -143,6 +143,31 @@ static inline int is_xen_skb(struct sk_buff *skb)
 	return (cp == skbuff_cachep);
 }
 
+/*
+ * We can flip without copying the packet unless:
+ *  1. The data is not allocated from our special cache; or
+ *  2. The main data area is shared; or
+ *  3. One or more fragments are shared; or
+ *  4. There are chained fragments.
+ */
+static inline int is_flippable_skb(struct sk_buff *skb)
+{
+	int frag;
+
+	if (!is_xen_skb(skb) || skb_cloned(skb))
+		return 0;
+
+	for (frag = 0; frag < skb_shinfo(skb)->nr_frags; frag++) {
+		if (page_count(skb_shinfo(skb)->frags[frag].page) > 1)
+			return 0;
+	}
+
+	if (skb_shinfo(skb)->frag_list != NULL)
+		return 0;
+
+	return 1;
+}
+
 static struct sk_buff *netbk_copy_skb(struct sk_buff *skb)
 {
 	struct skb_shared_info *ninfo;
@@ -152,6 +177,8 @@ static struct sk_buff *netbk_copy_skb(struct sk_buff *skb)
 	int len;
 	int headlen;
 
+	BUG_ON(skb_shinfo(skb)->frag_list != NULL);
+
 	nskb = alloc_skb(SKB_MAX_HEAD(0), GFP_ATOMIC);
 	if (unlikely(!nskb))
 		goto err;
@@ -252,11 +279,10 @@ int netif_be_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	/*
 	 * We do not copy the packet unless:
-	 *  1. The data is shared; or
+	 *  1. The data -- including any in fragments -- is shared; or
 	 *  2. The data is not allocated from our special cache.
-	 *  3. The data is fragmented.
 	 */
-	if (skb_cloned(skb) || skb_is_nonlinear(skb) || !is_xen_skb(skb)) {
+	if (!is_flippable_skb(skb)) {
 		struct sk_buff *nskb = netbk_copy_skb(skb);
 		if ( unlikely(nskb == NULL) )
 			goto drop;