[NET]: Zerocopy sequential reading of skb data

Implements sequential reading for both linear and non-linear
skb data at zerocopy cost. The data is returned in chunks of
arbitary length, therefore random access is not possible.

Usage:
	from	 := 0
	to	 := 128
	state	 := undef
	data	 := undef
	len	 := undef
	consumed := 0

	skb_prepare_seq_read(skb, from, to, &state)
	while (len = skb_seq_read(consumed, &data, &state)) != 0 do
		/* do something with 'data' of length 'len' */
		if abort then
			/* abort read if we don't wait for
			 * skb_seq_read() to return 0 */
			skb_abort_seq_read(&state)
			return
		endif
		/* not necessary to consume all of 'len' */
		consumed += len
	done

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index d7c839a21842..171a37dff83a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -321,6 +321,24 @@ extern void	      skb_over_panic(struct sk_buff *skb, int len,
 extern void           skb_under_panic(struct sk_buff *skb, int len,
                                       void *here);
 
+struct skb_seq_state
+{
+        __u32           lower_offset;
+        __u32           upper_offset;
+        __u32           frag_idx;
+        __u32           stepped_offset;
+        struct sk_buff  *root_skb;
+        struct sk_buff  *cur_skb;
+        __u8            *frag_data;
+};
+
+extern void           skb_prepare_seq_read(struct sk_buff *skb,
+                                           unsigned int from, unsigned int to,
+                                           struct skb_seq_state *st);
+extern unsigned int   skb_seq_read(unsigned int consumed, const u8 **data,
+                                   struct skb_seq_state *st);
+extern void           skb_abort_seq_read(struct skb_seq_state *st);
+
 /* Internal */
 #define skb_shinfo(SKB)         ((struct skb_shared_info *)((SKB)->end))