On Thu, 2012-04-12 at 16:42 +0900, Simon Horman wrote:
> This hook is based on a hook of the same name provided by UDP. It provides
> a way for to receive packets that have a TCP header and treat them in some
> alternate way.
>
> It is intended to be used by an implementation of the STT tunneling
> protocol within Open vSwtich's datapath. A prototype of such an
> implementation has been made.
>
> The STT draft is available at
> http://tools.ietf.org/html/draft-davie-stt-01
>
> My prototype STT implementation has been posted to the [email protected].
> The first version can be found at:
> http://www.mail-archive.com/[email protected]/msg08877.html
>
> Signed-off-by: Simon Horman <[email protected]>
>
Hi Simon
Oh well, this is insane :(
> ---
> include/linux/tcp.h | 3 +++
> net/ipv4/tcp_ipv4.c | 23 ++++++++++++++++++++++-
> 2 files changed, 25 insertions(+), 1 deletion(-)
>
> v3
> * First post to netdev
> * Replace more UDP references with TCP
> * Move socket accesses to inside socket lock
> and release lock on return.
>
> v2
> * Fix comment to refer to TCP rather than UDP
> * Allow skb to continue traversing the stack if
> the encap_rcv callback returns a positive value.
> This is the same behaviour as the UDP hook.
>
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index b6c62d2..7210b23 100644
> --- a/include/linux/tcp.h
> +++ b/include/linux/tcp.h
> @@ -472,6 +472,9 @@ struct tcp_sock {
> * contains related tcp_cookie_transactions fields.
> */
> struct tcp_cookie_values *cookie_values;
> +
> + /* For encapsulation sockets. */
> + int (*encap_rcv)(struct sock *sk, struct sk_buff *skb);
> };
>
This adds a new cache miss for all incoming tcp frames...
> static inline struct tcp_sock *tcp_sk(const struct sock *sk)
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 3a25cf7..9898f71 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1666,8 +1666,10 @@ int tcp_v4_rcv(struct sk_buff *skb)
> const struct iphdr *iph;
> const struct tcphdr *th;
> struct sock *sk;
> + struct tcp_sock *tp;
> int ret;
> struct net *net = dev_net(skb->dev);
> + int (*encap_rcv)(struct sock *sk, struct sk_buff *skb);
>
> if (skb->pkt_type != PACKET_HOST)
> goto discard_it;
> @@ -1726,9 +1728,27 @@ process:
>
> bh_lock_sock_nested(sk);
> ret = 0;
> +
> + tp = tcp_sk(sk);
> + encap_rcv = ACCESS_ONCE(tp->encap_rcv);
> + if (encap_rcv != NULL) {
and a new conditional...
> + /*
> + * This is an encapsulation socket so pass the skb to
> + * the socket's tcp_encap_rcv() hook. Otherwise, just
> + * fall through and pass this up the TCP socket.
> + * up->encap_rcv() returns the following value:
> + * <=0 if skb was successfully passed to the encap
> + * handler or was discarded by it.
> + * >0 if skb should be passed on to TCP.
> + */
> + if (encap_rcv(sk, skb) <= 0) {
> + ret = 0;
> + goto unlock_sock;
> + }
> + }
> +
> if (!sock_owned_by_user(sk)) {
> #ifdef CONFIG_NET_DMA
> - struct tcp_sock *tp = tcp_sk(sk);
> if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
> tp->ucopy.dma_chan = dma_find_channel(DMA_MEMCPY);
> if (tp->ucopy.dma_chan)
> @@ -1744,6 +1764,7 @@ process:
> NET_INC_STATS_BH(net, LINUX_MIB_TCPBACKLOGDROP);
> goto discard_and_relse;
> }
> +unlock_sock:
> bh_unlock_sock(sk);
>
> sock_put(sk);
I dont know, this sounds as a hack. Since you obviously spent a lot of
time on this stuff, lets be constructive.
I really suggest you take a look at <linux/static_key.h>
So that on machines without any need for this encap_rcv, we dont even
need to fetch tp->encap_rcv
if (static_key_false(&stt_active)) {
/* stt might be used on this socket */
encap_rcv = ACCESS_ONCE(tp->encap_rcv);
if (encap_rcv) {
...
}
}
This way, if stt is not used/loaded, we have a single NOP
If stt is used, NOP is patched to a JMP stt_code
I probably implement this idea on UDP shortly so that you can have a
reference for your implementation.
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