netback: Copy skbuffs that are presented to the start_xmit() function

with a multi-page head buffer. The new skbuff will not have a
multi-page head buffer, which is a necessary restriction until this is
supported by the internals of the netback driver.
Signed-off-by: Steven Smith <ssmith@xensource.com>
Signed-off-by: Keir Fraser <keir@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 98072726cb8c92858c58b7b05ae05e98cdc3d83c..5873b43c93d2f5890d414549ba3746c0ee44be6e 100644 (file)
--- a/linux-2.6-xen-sparse/drivers/xen/netback/netback.c
+++ b/linux-2.6-xen-sparse/drivers/xen/netback/netback.c
@@ -252,8 +252,11 @@ int netif_be_start_xmit(struct sk_buff *skb, struct net_device *dev)
        /*
         * Copy the packet here if it's destined for a flipping interface
         * but isn't flippable (e.g. extra references to data).
+        * XXX For now we also copy skbuffs whose head crosses a page
+        * boundary, because netbk_gop_skb can't handle them.
         */
-       if (!netif->copying_receiver) {
+       if (!netif->copying_receiver ||
+           ((skb_headlen(skb) + offset_in_page(skb->data)) >= PAGE_SIZE)) {
                struct sk_buff *nskb = netbk_copy_skb(skb);
                if ( unlikely(nskb == NULL) )
                        goto drop;
@@ -425,8 +428,9 @@ static void netbk_gop_skb(struct sk_buff *skb,
        }
 
        /*
-        * This must occur at the end to ensure that we don't trash
-        * skb_shinfo until we're done.
+        * This must occur at the end to ensure that we don't trash skb_shinfo
+        * until we're done. We know that the head doesn't cross a page
+        * boundary because such packets get copied in netif_be_start_xmit.
         */
        head_meta->id = netbk_gop_frag(netif, head_meta, 0, npo,
                                       virt_to_page(skb->data),