Re: [PATCH 7/7] net,ipv4,ipv6: Correct assignment of skb->network_header to skb->tail

This corrects an regression introduced by "net: Use 16bits for *_headers
fields of struct skbuff" when NET_SKBUFF_DATA_USES_OFFSET is not set. In
that case skb->tail will be a pointer however skb->network_header is now
an offset.

This patch corrects the problem by adding a wrapper to return skb tail as
an offset regardless of the value of NET_SKBUFF_DATA_USES_OFFSET. It seems
that skb->tail that this offset may be more than 64k and some care has been
taken to treat such cases as an error.

Signed-off-by: Simon Horman <horms@verge.net.au>
---
 include/linux/skbuff.h |    9 +++++++++
 net/core/netpoll.c     |    9 ++++++++-
 net/core/pktgen.c      |   16 ++++++++++++++--
 net/ipv4/ipmr.c        |    8 +++++++-
 4 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8f2b830..26ed287 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h

@@ -1391,6 +1391,11 @@ static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
 	skb_reset_tail_pointer(skb);
 	skb->tail += offset;
 }
+
+static inline __u64 skb_tail_offset(const struct sk_buff *skb)
+{
+	return skb->tail;
+}
 #else /* NET_SKBUFF_DATA_USES_OFFSET */
 static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
 {

@@ -1407,6 +1412,10 @@ static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
 	skb->tail = skb->data + offset;
 }
 
+static inline __u64 skb_tail_offset(const struct sk_buff *skb)
+{
+	return skb->tail - skb->head;
+}
 #endif /* NET_SKBUFF_DATA_USES_OFFSET */