dect
/
linux-2.6
Archived
13
0
Fork 0
Code Releases Activity

[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>
This commit is contained in:
Herbert Xu 2007-09-16 16:21:16 -07:00 committed by David S. Miller
parent e081e1e3ef
commit d9cc20484e
3 changed files with 33 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/net/pppoe.c
View File

@ -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 /* Copy the data if there is no space for the header or if it's
* read-only. * 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; goto abort;
__skb_push(skb, sizeof(*ph)); __skb_push(skb, sizeof(*ph));

40
include/linux/skbuff.h
View File

@ -1352,6 +1352,22 @@ static inline int skb_clone_writable(struct sk_buff *skb, int len)
skb_headroom(skb) + len <= skb->hdr_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_cow - copy header of skb when it is required
* @skb: buffer to cow * @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) static inline int skb_cow(struct sk_buff *skb, unsigned int headroom)
{ {
int delta = (headroom > NET_SKB_PAD ? headroom : NET_SKB_PAD) - return __skb_cow(skb, headroom, skb_cloned(skb));
skb_headroom(skb); }
if (delta < 0) /**
delta = 0; * skb_cow_head - skb_cow but only making the head writable
* @skb: buffer to cow
if (delta || skb_cloned(skb)) * @headroom: needed headroom
return pskb_expand_head(skb, (delta + (NET_SKB_PAD-1)) & *
~(NET_SKB_PAD-1), 0, GFP_ATOMIC); * This function is identical to skb_cow except that we replace the
return 0; * 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));
} }
/** /**

2
net/bridge/br_netfilter.c
View File

@ -183,7 +183,7 @@ int nf_bridge_copy_header(struct sk_buff *skb)
int err; int err;
int header_size = ETH_HLEN + nf_bridge_encap_header_len(skb); 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) if (err)
return err; return err;