netdev - [RFC][PATCH v4 08/18] Ignore skb_reserve() when device is using external buffer.

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Message-Id: <1272187206-18534-8-git-send-email-xiaohui.xin@intel.com>
Date:	Sun, 25 Apr 2010 17:19:55 +0800
From:	xiaohui.xin@...el.com
To:	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mst@...hat.com, mingo@...e.hu,
	davem@...emloft.net, jdike@...ux.intel.com
Cc:	Xin Xiaohui <xiaohui.xin@...el.com>
Subject: [RFC][PATCH v4 08/18] Ignore skb_reserve() when device is using external buffer.

From: Xin Xiaohui <xiaohui.xin@...el.com>

Make the skb->data and skb->head from external buffer
to be consistent, we ignore the room reserved by driver
for kernel skb.

Signed-off-by: Xin Xiaohui <xiaohui.xin@...el.com>
Signed-off-by: Zhao Yu <yzhao81@...il.com>
Reviewed-by: Jeff Dike <jdike@...ux.intel.com>
---
 include/linux/skbuff.h |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8949b15..4458dc8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1206,6 +1206,15 @@ static inline int skb_tailroom(const struct sk_buff *skb)
  */
 static inline void skb_reserve(struct sk_buff *skb, int len)
 {
+	/* Since skb_reserve() is only for an empty buffer,
+	 * and when the skb is getting external buffer, we cannot
+	 * retain the external buffer has the same reserved space
+	 * in the header which kernel allocatd skb has, so have to
+	 * ignore this. And we have recorded the external buffer
+	 * info in the destructor_arg field, so use it as indicator.
+	 */
+	if (skb_shinfo(skb)->destructor_arg)
+		return;
 	skb->data += len;
 	skb->tail += len;
 }
-- 
1.5.4.4

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