1 files changed, 64 insertions, 30 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 956130c70036..f3e591c611de 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -212,6 +212,49 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
         return false;
 }
 
+struct xenvif_count_slot_state {
+        unsigned long copy_off;
+        bool head;
+};
+
+unsigned int xenvif_count_frag_slots(struct xenvif *vif,
+                                     unsigned long offset, unsigned long size,
+                                     struct xenvif_count_slot_state *state)
+{
+        unsigned count = 0;
+
+        offset &= ~PAGE_MASK;
+
+        while (size > 0) {
+                unsigned long bytes;
+
+                bytes = PAGE_SIZE - offset;
+
+                if (bytes > size)
+                        bytes = size;
+
+                if (start_new_rx_buffer(state->copy_off, bytes, state->head)) {
+                        count++;
+                        state->copy_off = 0;
+                }
+
+                if (state->copy_off + bytes > MAX_BUFFER_OFFSET)
+                        bytes = MAX_BUFFER_OFFSET - state->copy_off;
+
+                state->copy_off += bytes;
+
+                offset += bytes;
+                size -= bytes;
+
+                if (offset == PAGE_SIZE)
+                        offset = 0;
+
+                state->head = false;
+        }
+
+        return count;
+}
+
 /*
  * Figure out how many ring slots we're going to need to send @skb to
  * the guest. This function is essentially a dry run of
@@ -219,48 +262,39 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
  */
 unsigned int xenvif_count_skb_slots(struct xenvif *vif, struct sk_buff *skb)
 {
+        struct xenvif_count_slot_state state;
         unsigned int count;
-        int i, copy_off;
+        unsigned char *data;
+        unsigned i;
 
-        count = DIV_ROUND_UP(skb_headlen(skb), PAGE_SIZE);
+        state.head = true;
+        state.copy_off = 0;
 
-        copy_off = skb_headlen(skb) % PAGE_SIZE;
+        /* Slot for the first (partial) page of data. */
+        count = 1;
 
+        /* Need a slot for the GSO prefix for GSO extra data? */
         if (skb_shinfo(skb)->gso_size)
                 count++;
 
-        for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
-                unsigned long size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
-                unsigned long offset = skb_shinfo(skb)->frags[i].page_offset;
-                unsigned long bytes;
-
-                offset &= ~PAGE_MASK;
-
-                while (size > 0) {
-                        BUG_ON(offset >= PAGE_SIZE);
-                        BUG_ON(copy_off > MAX_BUFFER_OFFSET);
-
-                        bytes = PAGE_SIZE - offset;
-
-                        if (bytes > size)
-                                bytes = size;
+        data = skb->data;
+        while (data < skb_tail_pointer(skb)) {
+                unsigned long offset = offset_in_page(data);
+                unsigned long size = PAGE_SIZE - offset;
 
-                        if (start_new_rx_buffer(copy_off, bytes, 0)) {
-                                count++;
-                                copy_off = 0;
-                        }
+                if (data + size > skb_tail_pointer(skb))
+                        size = skb_tail_pointer(skb) - data;
 
-                        if (copy_off + bytes > MAX_BUFFER_OFFSET)
-                                bytes = MAX_BUFFER_OFFSET - copy_off;
+                count += xenvif_count_frag_slots(vif, offset, size, &state);
 
-                        copy_off += bytes;
+                data += size;
+        }
 
-                        offset += bytes;
-                        size -= bytes;
+        for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+                unsigned long size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
+                unsigned long offset = skb_shinfo(skb)->frags[i].page_offset;
 
-                        if (offset == PAGE_SIZE)
-                                offset = 0;
-                }
+                count += xenvif_count_frag_slots(vif, offset, size, &state);
         }
         return count;
 }