[SK_BUFF]: Convert skb->tail to sk_buff_data_t

So that it is also an offset from skb->head, reduces its size from 8 to 4 bytes
on 64bit architectures, allowing us to combine the 4 bytes hole left by the
layer headers conversion, reducing struct sk_buff size to 256 bytes, i.e. 4
64byte cachelines, and since the sk_buff slab cache is SLAB_HWCACHE_ALIGN...
:-)

Many calculations that previously required that skb->{transport,network,
mac}_header be first converted to a pointer now can be done directly, being
meaningful as offsets or pointers.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 51 insertions, 18 deletions

diff --git a/include/linux/netfilter/nfnetlink.h b/include/linux/netfilter/nfnetlink.h
index 6179648a014e..e1ea5dfbbbd4 100644
--- a/include/linux/netfilter/nfnetlink.h
+++ b/include/linux/netfilter/nfnetlink.h
@@ -62,11 +62,11 @@ struct nfattr
 #define NFA_DATA(nfa)   ((void *)(((char *)(nfa)) + NFA_LENGTH(0)))
 #define NFA_PAYLOAD(nfa) ((int)((nfa)->nfa_len) - NFA_LENGTH(0))
 #define NFA_NEST(skb, type) \
-({      struct nfattr *__start = (struct nfattr *) (skb)->tail; \
+({      struct nfattr *__start = (struct nfattr *)skb_tail_pointer(skb); \
         NFA_PUT(skb, (NFNL_NFA_NEST | type), 0, NULL); \
         __start;  })
 #define NFA_NEST_END(skb, start) \
-({      (start)->nfa_len = ((skb)->tail - (unsigned char *) (start)); \
+({      (start)->nfa_len = skb_tail_pointer(skb) - (unsigned char *)(start); \
         (skb)->len; })
 #define NFA_NEST_CANCEL(skb, start) \
 ({      if (start) \
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index a9d3ad5bc80f..68a632b372ec 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -229,7 +229,7 @@ __nlmsg_put(struct sk_buff *skb, u32 pid, u32 seq, int type, int len, int flags)
                   (cb)->nlh->nlmsg_seq, type, len, flags)
 
 #define NLMSG_END(skb, nlh) \
-({      (nlh)->nlmsg_len = (skb)->tail - (unsigned char *) (nlh); \
+({      (nlh)->nlmsg_len = skb_tail_pointer(skb) - (unsigned char *)(nlh); \
         (skb)->len; })
 
 #define NLMSG_CANCEL(skb, nlh) \
diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 4a629ea70cc4..3a4cb242ecd2 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -605,7 +605,7 @@ extern void __rta_fill(struct sk_buff *skb, int attrtype, int attrlen, const voi
 
 #define RTA_PUT_NOHDR(skb, attrlen, data) \
 ({      RTA_APPEND(skb, RTA_ALIGN(attrlen), data); \
-        memset(skb->tail - (RTA_ALIGN(attrlen) - attrlen), 0, \
+        memset(skb_tail_pointer(skb) - (RTA_ALIGN(attrlen) - attrlen), 0, \
                RTA_ALIGN(attrlen) - attrlen); })
 
 #define RTA_PUT_U8(skb, attrtype, value) \
@@ -637,12 +637,12 @@ extern void __rta_fill(struct sk_buff *skb, int attrtype, int attrlen, const voi
         RTA_PUT(skb, attrtype, 0, NULL);
 
 #define RTA_NEST(skb, type) \
-({      struct rtattr *__start = (struct rtattr *) (skb)->tail; \
+({      struct rtattr *__start = (struct rtattr *)skb_tail_pointer(skb); \
         RTA_PUT(skb, type, 0, NULL); \
         __start;  })
 
 #define RTA_NEST_END(skb, start) \
-({      (start)->rta_len = ((skb)->tail - (unsigned char *) (start)); \
+({      (start)->rta_len = skb_tail_pointer(skb) - (unsigned char *)(start); \
         (skb)->len; })
 
 #define RTA_NEST_CANCEL(skb, start) \
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2e7405500626..e1c2392ecb56 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -246,9 +246,6 @@ struct sk_buff {
         int                     iif;
         /* 4 byte hole on 64 bit*/
 
-        sk_buff_data_t          transport_header;
-        sk_buff_data_t          network_header;
-        sk_buff_data_t          mac_header;
         struct  dst_entry       *dst;
         struct  sec_path        *sp;
 
@@ -303,13 +300,16 @@ struct sk_buff {
 
         __u32                   mark;
 
+        sk_buff_data_t          transport_header;
+        sk_buff_data_t          network_header;
+        sk_buff_data_t          mac_header;
         /* These elements must be at the end, see alloc_skb() for details.  */
-        unsigned int            truesize;
-        atomic_t                users;
+        sk_buff_data_t          tail;
         unsigned char           *head,
                                 *data,
-                                *tail,
                                 *end;
+        unsigned int            truesize;
+        atomic_t                users;
 };
 
 #ifdef __KERNEL__
@@ -812,12 +812,45 @@ static inline void skb_fill_page_desc(struct sk_buff *skb, int i,
 #define SKB_FRAG_ASSERT(skb)    BUG_ON(skb_shinfo(skb)->frag_list)
 #define SKB_LINEAR_ASSERT(skb)  BUG_ON(skb_is_nonlinear(skb))
 
+#ifdef NET_SKBUFF_DATA_USES_OFFSET
+static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
+{
+        return skb->head + skb->tail;
+}
+
+static inline void skb_reset_tail_pointer(struct sk_buff *skb)
+{
+        skb->tail = skb->data - skb->head;
+}
+
+static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
+{
+        skb_reset_tail_pointer(skb);
+        skb->tail += offset;
+}
+#else /* NET_SKBUFF_DATA_USES_OFFSET */
+static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
+{
+        return skb->tail;
+}
+
+static inline void skb_reset_tail_pointer(struct sk_buff *skb)
+{
+        skb->tail = skb->data;
+}
+
+static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
+{
+        skb->tail = skb->data + offset;
+}
+#endif /* NET_SKBUFF_DATA_USES_OFFSET */
+
 /*
  *      Add data to an sk_buff
  */
 static inline unsigned char *__skb_put(struct sk_buff *skb, unsigned int len)
 {
-        unsigned char *tmp = skb->tail;
+        unsigned char *tmp = skb_tail_pointer(skb);
         SKB_LINEAR_ASSERT(skb);
         skb->tail += len;
         skb->len  += len;
@@ -835,11 +868,11 @@ static inline unsigned char *__skb_put(struct sk_buff *skb, unsigned int len)
  */
 static inline unsigned char *skb_put(struct sk_buff *skb, unsigned int len)
 {
-        unsigned char *tmp = skb->tail;
+        unsigned char *tmp = skb_tail_pointer(skb);
         SKB_LINEAR_ASSERT(skb);
         skb->tail += len;
         skb->len  += len;
-        if (unlikely(skb->tail>skb->end))
+        if (unlikely(skb_tail_pointer(skb) > skb->end))
                 skb_over_panic(skb, len, current_text_addr());
         return tmp;
 }
@@ -935,7 +968,7 @@ static inline int skb_headroom(const struct sk_buff *skb)
  */
 static inline int skb_tailroom(const struct sk_buff *skb)
 {
-        return skb_is_nonlinear(skb) ? 0 : skb->end - skb->tail;
+        return skb_is_nonlinear(skb) ? 0 : skb->end - skb_tail_pointer(skb);
 }
 
 /**
@@ -1127,8 +1160,8 @@ static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
                 WARN_ON(1);
                 return;
         }
-        skb->len  = len;
-        skb->tail = skb->data + len;
+        skb->len = len;
+        skb_set_tail_pointer(skb, len);
 }
 
 /**