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;
 }