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authorHerbert Xu <herbert@gondor.apana.org.au>2007-09-16 16:21:16 -0700
committerDavid S. Miller <davem@davemloft.net>2007-09-16 16:21:16 -0700
commitd9cc20484e5e48c6a5deb4387c20fd45bfbdde8c (patch)
treef0a9f05ad00b8a506abeb3b42cb3346cef7d2155
parente081e1e3ef4682802ac63b1e5e26158fb9ca9e90 (diff)
downloadlinux-linaro-d9cc20484e5e48c6a5deb4387c20fd45bfbdde8c.tar.gz
[NET] skbuff: Add skb_cow_head
This patch adds an optimised version of skb_cow that avoids the copy if the header can be modified even if the rest of the payload is cloned. This can be used in encapsulating paths where we only need to modify the header. As it is, this can be used in PPPOE and bridging. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--drivers/net/pppoe.c2
-rw-r--r--include/linux/skbuff.h40
-rw-r--r--net/bridge/br_netfilter.c2
3 files changed, 33 insertions, 11 deletions
diff --git a/drivers/net/pppoe.c b/drivers/net/pppoe.c
index bac36546e0b..0d7f570b9a5 100644
--- a/drivers/net/pppoe.c
+++ b/drivers/net/pppoe.c
@@ -860,7 +860,7 @@ static int __pppoe_xmit(struct sock *sk, struct sk_buff *skb)
/* Copy the data if there is no space for the header or if it's
* read-only.
*/
- if (skb_cow(skb, sizeof(*ph) + dev->hard_header_len))
+ if (skb_cow_head(skb, sizeof(*ph) + dev->hard_header_len))
goto abort;
__skb_push(skb, sizeof(*ph));
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 93c27f71122..a656cecd373 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1352,6 +1352,22 @@ static inline int skb_clone_writable(struct sk_buff *skb, int len)
skb_headroom(skb) + len <= skb->hdr_len;
}
+static inline int __skb_cow(struct sk_buff *skb, unsigned int headroom,
+ int cloned)
+{
+ int delta = 0;
+
+ if (headroom < NET_SKB_PAD)
+ headroom = NET_SKB_PAD;
+ if (headroom > skb_headroom(skb))
+ delta = headroom - skb_headroom(skb);
+
+ if (delta || cloned)
+ return pskb_expand_head(skb, ALIGN(delta, NET_SKB_PAD), 0,
+ GFP_ATOMIC);
+ return 0;
+}
+
/**
* skb_cow - copy header of skb when it is required
* @skb: buffer to cow
@@ -1366,16 +1382,22 @@ static inline int skb_clone_writable(struct sk_buff *skb, int len)
*/
static inline int skb_cow(struct sk_buff *skb, unsigned int headroom)
{
- int delta = (headroom > NET_SKB_PAD ? headroom : NET_SKB_PAD) -
- skb_headroom(skb);
-
- if (delta < 0)
- delta = 0;
+ return __skb_cow(skb, headroom, skb_cloned(skb));
+}
- if (delta || skb_cloned(skb))
- return pskb_expand_head(skb, (delta + (NET_SKB_PAD-1)) &
- ~(NET_SKB_PAD-1), 0, GFP_ATOMIC);
- return 0;
+/**
+ * skb_cow_head - skb_cow but only making the head writable
+ * @skb: buffer to cow
+ * @headroom: needed headroom
+ *
+ * This function is identical to skb_cow except that we replace the
+ * skb_cloned check by skb_header_cloned. It should be used when
+ * you only need to push on some header and do not need to modify
+ * the data.
+ */
+static inline int skb_cow_head(struct sk_buff *skb, unsigned int headroom)
+{
+ return __skb_cow(skb, headroom, skb_header_cloned(skb));
}
/**
diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index 3ee2022928e..fc13130035e 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -183,7 +183,7 @@ int nf_bridge_copy_header(struct sk_buff *skb)
int err;
int header_size = ETH_HLEN + nf_bridge_encap_header_len(skb);
- err = skb_cow(skb, header_size);
+ err = skb_cow_head(skb, header_size);
if (err)
return err;