netfilter: move nat hlist_head to nf_conn
The nat extension structure is 32bytes in size on x86_64:
struct nf_conn_nat {
struct hlist_node bysource; /* 0 16 */
struct nf_conn * ct; /* 16 8 */
union nf_conntrack_nat_help help; /* 24 4 */
int masq_index; /* 28 4 */
/* size: 32, cachelines: 1, members: 4 */
/* last cacheline: 32 bytes */
};
The hlist is needed to quickly check for possible tuple collisions
when installing a new nat binding. Storing this in the extension
area has two drawbacks:
1. We need ct backpointer to get the conntrack struct from the extension.
2. When reallocation of extension area occurs we need to fixup the bysource
hash head via hlist_replace_rcu.
We can avoid both by placing the hlist_head in nf_conn and place nf_conn in
the bysource hash rather than the extenstion.
We can also remove the ->move support; no other extension needs it.
Moving the entire nat extension into nf_conn would be possible as well but
then we have to add yet another callback for deletion from the bysource
hash table rather than just using nat extension ->destroy hook for this.
nf_conn size doesn't increase due to aligment, followup patch replaces
hlist_node with single pointer.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
5 files changed