[PATCH] add skb_pad/skb_padto functionality

This is the stuff in 2.4 which DaveM has been over so I hope is ok for 2.5.
It provides a simple API for driver writers with hardware that doesn't
do packet padding to say 'make sure n bytes beyond the data is all clear'
for DMA etc.

1 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f94999dcfb1c..e364ce6c003c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -287,6 +287,7 @@ extern struct sk_buff *skb_realloc_headroom(struct sk_buff *skb,
 extern struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
 				       int newheadroom, int newtailroom,
 				       int priority);
+extern struct sk_buff *		skb_pad(struct sk_buff *skb, int pad);
 #define dev_kfree_skb(a)	kfree_skb(a)
 extern void	      skb_over_panic(struct sk_buff *skb, int len,
 				     void *here);
@@ -1088,6 +1089,26 @@ static inline int skb_cow(struct sk_buff *skb, unsigned int headroom)
 }
 
 /**
+ *	skb_padto	- pad an skbuff up to a minimal size
+ *	@skb: buffer to pad
+ *	@len: minimal length
+ *
+ *	Pads up a buffer to ensure the trailing bytes exist and are
+ *	blanked. If the buffer already contains sufficient data it
+ *	is untouched. Returns the buffer, which may be a replacement
+ *	for the original, or NULL for out of memory - in which case
+ *	the original buffer is still freed.
+ */
+ 
+static inline struct sk_buff *skb_padto(struct sk_buff *skb, unsigned int len)
+{
+	unsigned int size = skb->len + skb->data_len;
+	if (likely(size >= len))
+		return skb;
+	return skb_pad(skb, len-size);
+}
+
+/**
  *	skb_linearize - convert paged skb to linear one
  *	@skb: buffer to linarize
  *	@gfp: allocation mode