From 1d0c0b328a63826b7c80c27d1c4f2b04e8225273 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Fri, 27 Apr 2012 02:10:03 +0000
Subject: [PATCH] net: makes skb_splice_bits() aware of skb->head_frag
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__skb_splice_bits() can check if skb to be spliced has its skb->head
mapped to a page fragment, instead of a kmalloc() area.

If so we can avoid a copy of the skb head and get a reference on
underlying page.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: Matt Carlson <mcarlson@broadcom.com>
Cc: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 net/core/skbuff.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 09cc386..52ba2b5 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1699,14 +1699,18 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
 			      struct splice_pipe_desc *spd, struct sock *sk)
 {
 	int seg;
+	bool head_is_linear = !skb->head_frag;
 
-	/*
-	 * map the linear part
+	/* map the linear part :
+	 * If skb->head_frag is set, this 'linear' part is backed
+	 * by a fragment, and we can avoid a copy.
 	 */
 	if (__splice_segment(virt_to_page(skb->data),
 			     (unsigned long) skb->data & (PAGE_SIZE - 1),
 			     skb_headlen(skb),
-			     offset, len, skb, spd, true, sk, pipe))
+			     offset, len, skb, spd,
+			     head_is_linear,
+			     sk, pipe))
 		return true;
 
 	/*
-- 
2.7.4