From d6301d3dd1c287b32132dda15272a50c11e92a14 Mon Sep 17 00:00:00 2001 From: "David S. Miller" Date: Sun, 8 Feb 2009 19:24:13 -0800 Subject: [PATCH] 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: David S. Miller --- include/linux/skbuff.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 08670d017479..5eba4007e07f 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -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); -- 2.20.1