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Commit d6301d3d authored by David S. Miller's avatar David S. Miller
Browse files

net: Increase default NET_SKB_PAD to 32. 



Several devices need to insert some "pre headers" in front of the
main packet data when they transmit a packet.

Currently we allocate only 16 bytes of pad room and this ends up not
being enough for some types of hardware (NIU, usb-net, s390 qeth,
etc.)

So increase this to 32.

Note that drivers still need to check in their transmit routine
whether enough headroom exists, and if not use skb_realloc_headroom().
Tunneling, IPSEC, and other encapsulation methods can cause the
padding area to be used up.

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 409f0a90

include/linux/skbuff.h

+3 −3
Original line number Diff line number Diff line
@@ -1287,7 +1287,7 @@ static inline int skb_network_offset(const struct sk_buff *skb) 
 * The networking layer reserves some headroom in skb data (via

 * dev_alloc_skb). This is used to avoid having to reallocate skb data when

 * the header has to grow. In the default case, if the header has to grow

 * 16 bytes or less we avoid the reallocation.

 * 32 bytes or less we avoid the reallocation.

 *

 * Unfortunately this headroom changes the DMA alignment of the resulting

 * network packet. As for NET_IP_ALIGN, this unaligned DMA is expensive
@@ -1295,11 +1295,11 @@ static inline int skb_network_offset(const struct sk_buff *skb) 
 * perhaps setting it to a cacheline in size (since that will maintain

 * cacheline alignment of the DMA). It must be a power of 2.

 *

 * Various parts of the networking layer expect at least 16 bytes of

 * Various parts of the networking layer expect at least 32 bytes of

 * headroom, you should not reduce this.

 */

#ifndef NET_SKB_PAD

#define NET_SKB_PAD	16

#define NET_SKB_PAD	32

#endif



extern int ___pskb_trim(struct sk_buff *skb, unsigned int len);