tipc: extract bundled buffers by cloning instead of copying

When we currently extract a bundled buffer from a message bundle in
the function tipc_msg_extract(), we allocate a new buffer and explicitly
copy the linear data area.

This is unnecessary, since we can just clone the buffer and do
skb_pull() on the clone to move the data pointer to the correct
position.

This is what we do in this commit.
Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/link.c

 /*
  * net/tipc/link.c: TIPC link code
  *
- * Copyright (c) 1996-2007, 2012-2014, Ericsson AB
+ * Copyright (c) 1996-2007, 2012-2015, Ericsson AB
  * Copyright (c) 2004-2007, 2010-2013, Wind River Systems
  * All rights reserved.
  *
@@ -1117,7 +1117,7 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b_ptr)
 		ackd = msg_ack(msg);
 
 		/* Release acked messages */
-		if (n_ptr->bclink.recv_permitted)
+		if (likely(n_ptr->bclink.recv_permitted))
 			tipc_bclink_acknowledge(n_ptr, msg_bcast_ack(msg));
 
 		released = 0;
@@ -1712,45 +1712,24 @@ void tipc_link_dup_queue_xmit(struct tipc_link *l_ptr,
 	}
 }
 
-/**
- * buf_extract - extracts embedded TIPC message from another message
- * @skb: encapsulating message buffer
- * @from_pos: offset to extract from
- *
- * Returns a new message buffer containing an embedded message.  The
- * encapsulating buffer is left unchanged.
- */
-static struct sk_buff *buf_extract(struct sk_buff *skb, u32 from_pos)
-{
-	struct tipc_msg *msg = (struct tipc_msg *)(skb->data + from_pos);
-	u32 size = msg_size(msg);
-	struct sk_buff *eb;
-
-	eb = tipc_buf_acquire(size);
-	if (eb)
-		skb_copy_to_linear_data(eb, msg, size);
-	return eb;
-}
-
 /* tipc_link_dup_rcv(): Receive a tunnelled DUPLICATE_MSG packet.
  * Owner node is locked.
  */
-static void tipc_link_dup_rcv(struct tipc_link *l_ptr,
-			      struct sk_buff *t_buf)
+static void tipc_link_dup_rcv(struct tipc_link *link,
+			      struct sk_buff *skb)
 {
-	struct sk_buff *buf;
+	struct sk_buff *iskb;
+	int pos = 0;
 
-	if (!tipc_link_is_up(l_ptr))
+	if (!tipc_link_is_up(link))
 		return;
 
-	buf = buf_extract(t_buf, INT_H_SIZE);
-	if (buf == NULL) {
+	if (!tipc_msg_extract(skb, &iskb, &pos)) {
 		pr_warn("%sfailed to extract inner dup pkt\n", link_co_err);
 		return;
 	}
-
-	/* Add buffer to deferred queue, if applicable: */
-	link_handle_out_of_seq_msg(l_ptr, buf);
+	/* Append buffer to deferred queue, if applicable: */
+	link_handle_out_of_seq_msg(link, iskb);
 }
 
 /*  tipc_link_failover_rcv(): Receive a tunnelled ORIGINAL_MSG packet
@@ -1762,6 +1741,7 @@ static struct sk_buff *tipc_link_failover_rcv(struct tipc_link *l_ptr,
 	struct tipc_msg *t_msg = buf_msg(t_buf);
 	struct sk_buff *buf = NULL;
 	struct tipc_msg *msg;
+	int pos = 0;
 
 	if (tipc_link_is_up(l_ptr))
 		tipc_link_reset(l_ptr);
@@ -1773,8 +1753,7 @@ static struct sk_buff *tipc_link_failover_rcv(struct tipc_link *l_ptr,
 	/* Should there be an inner packet? */
 	if (l_ptr->exp_msg_count) {
 		l_ptr->exp_msg_count--;
-		buf = buf_extract(t_buf, INT_H_SIZE);
-		if (buf == NULL) {
+		if (!tipc_msg_extract(t_buf, &buf, &pos)) {
 			pr_warn("%sno inner failover pkt\n", link_co_err);
 			goto exit;
 		}

net/tipc/msg.c

@@ -372,38 +372,40 @@ bool tipc_msg_bundle(struct sk_buff_head *list, struct sk_buff *skb, u32 mtu)
 
 /**
  *  tipc_msg_extract(): extract bundled inner packet from buffer
- *  @skb: linear outer buffer, to be extracted from.
+ *  @skb: buffer to be extracted from.
  *  @iskb: extracted inner buffer, to be returned
- *  @pos: position of msg to be extracted. Returns with pointer of next msg
+ *  @pos: position in outer message of msg to be extracted.
+ *        Returns position of next msg
  *  Consumes outer buffer when last packet extracted
  *  Returns true when when there is an extracted buffer, otherwise false
  */
 bool tipc_msg_extract(struct sk_buff *skb, struct sk_buff **iskb, int *pos)
 {
 	struct tipc_msg *msg;
-	int imsz;
-	struct tipc_msg *imsg;
+	int imsz, offset;
 
+	*iskb = NULL;
 	if (unlikely(skb_linearize(skb)))
-		return false;
+		goto none;
+
 	msg = buf_msg(skb);
-	imsg = (struct tipc_msg *)(msg_data(msg) + *pos);
-	/* Is there space left for shortest possible message? */
-	if (*pos > (msg_data_sz(msg) - SHORT_H_SIZE))
+	offset = msg_hdr_sz(msg) + *pos;
+	if (unlikely(offset > (msg_size(msg) - MIN_H_SIZE)))
 		goto none;
-	imsz = msg_size(imsg);
 
-	/* Is there space left for current message ? */
-	if ((*pos + imsz) > msg_data_sz(msg))
+	*iskb = skb_clone(skb, GFP_ATOMIC);
+	if (unlikely(!*iskb))
 		goto none;
-	*iskb = tipc_buf_acquire(imsz);
-	if (!*iskb)
+	skb_pull(*iskb, offset);
+	imsz = msg_size(buf_msg(*iskb));
+	skb_trim(*iskb, imsz);
+	if (unlikely(!tipc_msg_validate(*iskb)))
 		goto none;
-	skb_copy_to_linear_data(*iskb, imsg, imsz);
 	*pos += align(imsz);
 	return true;
 none:
 	kfree_skb(skb);
+	kfree_skb(*iskb);
 	*iskb = NULL;
 	return false;
 }