[NETFILTER]: reduce netfilter sk_buff enlargement

As discussed at netconf'05, we're trying to save every bit in sk_buff.
The patch below makes sk_buff 8 bytes smaller.  I did some basic
testing on my notebook and it seems to work.

The only real in-tree user of nfcache was IPVS, who only needs a
single bit.  Unfortunately I couldn't find some other free bit in
sk_buff to stuff that bit into, so I introduced a separate field for
them.  Maybe the IPVS guys can resolve that to further save space.

Initially I wanted to shrink pkt_type to three bits (PACKET_HOST and
alike are only 6 values defined), but unfortunately the bluetooth code
overloads pkt_type :(

The conntrack-event-api (out-of-tree) uses nfcache, but Rusty just
came up with a way how to do it without any skb fields, so it's safe
to remove it.

- remove all never-implemented 'nfcache' code
- don't have ipvs code abuse 'nfcache' field. currently get's their own
  compile-conditional skb->ipvs_property field.  IPVS maintainers can
  decide to move this bit elswhere, but nfcache needs to die.
- remove skb->nfcache field to save 4 bytes
- move skb->nfctinfo into three unused bits to save further 4 bytes

Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 17 insertions, 5 deletions

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index 2e2045482cb1..ec60856408fd 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -21,10 +21,13 @@
 #define NF_STOP 5
 #define NF_MAX_VERDICT NF_STOP
 
+/* only for userspace compatibility */
+#ifndef __KERNEL__
 /* Generic cache responses from hook functions.
    <= 0x2000 is used for protocol-flags. */
 #define NFC_UNKNOWN 0x4000
 #define NFC_ALTERED 0x8000
+#endif
 
 #ifdef __KERNEL__
 #include <linux/config.h>
diff --git a/include/linux/netfilter_decnet.h b/include/linux/netfilter_decnet.h
index 3064eec9cb8e..018979484150 100644
--- a/include/linux/netfilter_decnet.h
+++ b/include/linux/netfilter_decnet.h
@@ -9,6 +9,8 @@
 
 #include <linux/netfilter.h>
 
+/* only for userspace compatibility */
+#ifndef __KERNEL__
 /* IP Cache bits. */
 /* Src IP address. */
 #define NFC_DN_SRC              0x0001
@@ -18,6 +20,7 @@
 #define NFC_DN_IF_IN            0x0004
 /* Output device. */
 #define NFC_DN_IF_OUT           0x0008
+#endif /* ! __KERNEL__ */
 
 /* DECnet Hooks */
 /* After promisc drops, checksum checks. */
diff --git a/include/linux/netfilter_ipv4.h b/include/linux/netfilter_ipv4.h
index 3ebc36afae1a..552815b8193e 100644
--- a/include/linux/netfilter_ipv4.h
+++ b/include/linux/netfilter_ipv4.h
@@ -8,6 +8,8 @@
 #include <linux/config.h>
 #include <linux/netfilter.h>
 
+/* only for userspace compatibility */
+#ifndef __KERNEL__
 /* IP Cache bits. */
 /* Src IP address. */
 #define NFC_IP_SRC              0x0001
@@ -35,6 +37,7 @@
 #define NFC_IP_DST_PT           0x0400
 /* Something else about the proto */
 #define NFC_IP_PROTO_UNKNOWN    0x2000
+#endif /* ! __KERNEL__ */
 
 /* IP Hooks */
 /* After promisc drops, checksum checks. */
diff --git a/include/linux/netfilter_ipv6.h b/include/linux/netfilter_ipv6.h
index bee7a5ec7c66..20c069a5e4ac 100644
--- a/include/linux/netfilter_ipv6.h
+++ b/include/linux/netfilter_ipv6.h
@@ -10,6 +10,8 @@
 
 #include <linux/netfilter.h>
 
+/* only for userspace compatibility */
+#ifndef __KERNEL__
 /* IP Cache bits. */
 /* Src IP address. */
 #define NFC_IP6_SRC              0x0001
@@ -38,6 +40,7 @@
 #define NFC_IP6_DST_PT           0x0400
 /* Something else about the proto */
 #define NFC_IP6_PROTO_UNKNOWN    0x2000
+#endif /* ! __KERNEL__ */
 
 
 /* IP6 Hooks */
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2e40f4c9f7a6..4b929c3c1a98 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -190,7 +190,6 @@ struct skb_shared_info {
  *      @end: End pointer
  *      @destructor: Destruct function
  *      @nfmark: Can be used for communication between hooks
- *      @nfcache: Cache info
  *      @nfct: Associated connection, if any
  *      @nfctinfo: Relationship of this skb to the connection
  *      @nf_bridge: Saved data about a bridged frame - see br_netfilter.c
@@ -252,17 +251,18 @@ struct sk_buff {
         __u8                    local_df:1,
                                 cloned:1,
                                 ip_summed:2,
-                                nohdr:1;
-                                /* 3 bits spare */
+                                nohdr:1,
+                                nfctinfo:3;
         __u8                    pkt_type;
         __be16                  protocol;
 
         void                    (*destructor)(struct sk_buff *skb);
 #ifdef CONFIG_NETFILTER
         __u32                   nfmark;
-        __u32                   nfcache;
-        __u32                   nfctinfo;
         struct nf_conntrack     *nfct;
+#if defined(CONFIG_IP_VS) || defined(CONFIG_IP_VS_MODULE)
+        __u8                    ipvs_property:1;
+#endif
 #ifdef CONFIG_BRIDGE_NETFILTER
         struct nf_bridge_info   *nf_bridge;
 #endif