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 <davem@davemloft.net>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 08670d0..5eba400 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1287,7 +1287,7 @@
* 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 @@
* 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);