[PATCH] net-tcp: TCP/IP stack bypass for loopback connections

Bruce "Brutus" Curtis
2012-08-07T21:09:02Z

From: "Bruce \"Brutus\" Curtis" <brutus@google.com>

TCP/IP loopback socket pair stack bypass, based on an idea by, and
rough upstream patch from, David Miller <davem@davemloft.net> called
"friends", the data structure modifcations and connection scheme are
reused with extensive data-path changes.

A new sysctl, net.ipv4.tcp_friends, is added:
0: disable friends and use the stock data path.
1: enable friends and bypass the stack data path, the default.

Note, when friends is enabled any loopback interpose, e.g. tcpdump,
will only see the TCP/IP packets during connection establishment and
finish, all data bypasses the stack and instead is delivered to the
destination socket directly.

Testing done on a 4 socket 2.2GHz "Quad-Core AMD Opteron(tm) Processor
8354 CPU" based system, netperf results for a single connection show
increased TCP_STREAM throughput, increased TCP_RR and TCP_CRR transaction
rate for most message sizes vs baseline and comparable to AF_UNIX.

Significant increase (up to 5x) in aggregate throughput for multiple
netperf runs (STREAM 32KB I/O x N) is seen.

Some results:

Default netperf: netperf
netperf -t STREAM_STREAM
netperf -t STREAM_STREAM -- -s 51882 -m 16384 -M 87380
netperf

Baseline AF_UNIX AF_UNIX Friends
Mbits/S Mbits/S Mbits/S Mbits/S
6860 714 8% 9444 138% 1323% 10576 154% 1481% 112%

Note, for the AF_UNIX (STREAM_STREAM) test 2 results are listed, 1st
with no options but as the defaults for AF_UNIX sockets are much lower
performaning a 2nd set of runs with a socket buffer size and send/recv
buffer sizes equivalent to AF_INET (TCP_STREAM) are done.

Note, all subsequent AF_UNIX (STREAM_STREAM, STREAM_RR) tests are done
with "-s 51882" such that the same total effective socket buffering is
used as for the AF_INET runs defaults (16384+NNNNN/2).

STREAM 32KB I/O x N: netperf -l 100 -t TCP_STREAM -- -m 32K -M 32K
netperf -l 100 -t STREAM_STREAM -- -s 51882 -m 32K -M 32K
netperf -l 100 -t TCP_STREAM -- -m 32K -M 32K

Baseline AF_UNIX Friends
N COC Mbits/S Mbits/S Mbits/S
1 - 8616 9416 109% 11116 129% 118%
2 - 15419 17076 111% 20267 131% 119%
16 2 59497 303029 509% 347349 584% 115%
32 4 54223 273637 505% 272891 503% 100%
256 32 58244 85476 147% 273696 470% 320%
512 64 58745 87402 149% 260837 444% 298%
1600 200 83161 158915 191% 383947 462% 242%

COC = Cpu Over Commit ratio (16 core platform)

STREAM: netperf -l 100 -t TCP_STREAM
netperf -l 100 -t STREAM_STREAM -- -s 51882
netperf -l 100 -t TCP_STREAM

netperf Baseline AF_UNIX Friends
-m/-M N Mbits/S Mbits/S Mbits/S
64 1020 445 44% 515 50% 116%
1K 4881 4340 89% 5070 104% 117%
8K 5933 8387 141% 9770 165% 116%
32K 8168 9538 117% 11067 135% 116%
64K 9116 9774 107% 11515 126% 118%
128K 9053 10044 111% 13082 145% 130%
256K 9642 10351 107% 13470 140% 130%
512K 10050 10142 101% 13327 133% 131%
1M 8640 9843 114% 12201 141% 124%
16M 7179 9619 134% 11316 158% 118%

RR: netperf -l 100 -t TCP_RR
netperf -l 100 -t STREAM_RR -- -s 51882 -m 16384 -M 87380
netperf -l 100 -t TCP_RR

netperf Baseline AF_UNIX Friends
-r N,N Trans./S Trans./S Trans./S
64 47913 99681 208% 98225 205% 99%
1K 44045 92327 210% 91608 208% 99%
8K 26732 33201 124% 33025 124% 99%
32K 10903 11972 110% 13574 124% 113%
64K 7113 6718 94% 7176 101% 107%
128K 4191 3431 82% 3695 88% 108%
256K 2324 1937 83% 2147 92% 111%
512K 958 1056 110% 1202 125% 114%
1M 404 508 126% 497 123% 98%
16M 26.1 34.1 131% 32.9 126% 96%

CRR: netperf -l 100 -t TCP_CRR
netperf -l 100 -t TCP_CRR

netperf Baseline AF_UNIX Friends
-r N Trans./S Trans./S Trans./S
64 14690 - 18191 124% -
1K 14258 - 17492 123% -
8K 11535 - 14012 121% -
32K 7035 - 8974 128% -
64K 4312 - 5654 131% -
128K 2252 - 3179 141% -
256K 1237 - 2008 162% -
512K 17.5* - 1079 ? -
1M 4.93* - 458 ? -
16M 8.29* - 32.5 ? -

Note, "-" denotes test not supported for transport.
"*" denotes test results reported without statistical confidence.
"?" denotes results not comparable.

SPLICE 32KB I/O:

Source
Sink Baseline Friends
FSFS Mbits/S Mbits/S
---- 8042 10810 134%
Z--- 7071 9773 138%
--N- 8039 10820 135%
Z-N- 7902 9796 124%
-S-- 17326 37496 216%
ZS-- 9008 9573 106%
-SN- 16154 36269 225%
ZSN- 9531 9640 101%
---S 8466 9933 117%
Z--S 8000 9453 118%
--NS 12783 11379 89%
Z-NS 11055 9489 86%
-S-S 12741 24380 191%
ZS-S 8097 10242 126%
-SNS 16657 30954 186%
ZSNS 12108 12763 105%

Note, "Z" source File /dev/zero, "-" source user memory
"N" sink File /dev/null, "-" sink user memory
"S" Splice on, "-" Splice off

Signed-off-by: Bruce \"Brutus\" Curtis <brutus@google.com>
---
include/linux/skbuff.h | 2 +
include/net/request_sock.h | 1 +
include/net/sock.h | 32 +++-
include/net/tcp.h | 3 +-
net/core/skbuff.c | 1 +
net/core/sock.c | 1 +
net/core/stream.c | 36 +++
net/ipv4/inet_connection_sock.c | 20 ++
net/ipv4/sysctl_net_ipv4.c | 7 +
net/ipv4/tcp.c | 500 ++++++++++++++++++++++++++++++++++-----
net/ipv4/tcp_input.c | 22 ++-
net/ipv4/tcp_ipv4.c | 2 +
net/ipv4/tcp_minisocks.c | 5 +
net/ipv4/tcp_output.c | 18 ++-
net/ipv6/tcp_ipv6.c | 1 +
15 files changed, 576 insertions(+), 75 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 642cb73..2fbca93 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -332,6 +332,7 @@ typedef unsigned char *sk_buff_data_t;
* @cb: Control buffer. Free for use by every layer. Put private vars here
* @_skb_refdst: destination entry (with norefcount bit)
* @sp: the security path, used for xfrm
+ * @friend: loopback friend socket
* @len: Length of actual data
* @data_len: Data length
* @mac_len: Length of link layer header
@@ -407,6 +408,7 @@ struct sk_buff {
#ifdef CONFIG_XFRM
struct sec_path *sp;
#endif
+ struct sock *friend;
unsigned int len,
data_len;
__u16 mac_len,
diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index 4c0766e..2c74420 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -63,6 +63,7 @@ struct request_sock {
unsigned long expires;
const struct request_sock_ops *rsk_ops;
struct sock *sk;
+ struct sock *friend;
u32 secid;
u32 peer_secid;
};
diff --git a/include/net/sock.h b/include/net/sock.h
index dcb54a0..3b371f5 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -197,6 +197,7 @@ struct cg_proto;
* @sk_userlocks: %SO_SNDBUF and %SO_RCVBUF settings
* @sk_lock: synchronizer
* @sk_rcvbuf: size of receive buffer in bytes
+ * @sk_friend: loopback friend socket
* @sk_wq: sock wait queue and async head
* @sk_rx_dst: receive input route used by early tcp demux
* @sk_dst_cache: destination cache
@@ -286,6 +287,14 @@ struct sock {
socket_lock_t sk_lock;
struct sk_buff_head sk_receive_queue;
/*
+ * If socket has a friend (sk_friend != NULL) then a send skb is
+ * enqueued directly to the friend's sk_receive_queue such that:
+ *
+ * sk_sndbuf -> sk_sndbuf + sk_friend->sk_rcvbuf
+ * sk_wmem_queued -> sk_friend->sk_rmem_alloc
+ */
+ struct sock *sk_friend;
+ /*
* The backlog queue is special, it is always used with
* the per-socket spinlock held and requires low latency
* access. Therefore we special case it's implementation.
@@ -673,24 +682,40 @@ static inline bool sk_acceptq_is_full(const struct sock *sk)
return sk->sk_ack_backlog > sk->sk_max_ack_backlog;
}

+static inline int sk_wmem_queued_get(const struct sock *sk)
+{
+ if (sk->sk_friend)
+ return atomic_read(&sk->sk_friend->sk_rmem_alloc);
+ else
+ return sk->sk_wmem_queued;
+}
+
+static inline int sk_sndbuf_get(const struct sock *sk)
+{
+ if (sk->sk_friend)
+ return sk->sk_sndbuf + sk->sk_friend->sk_rcvbuf;
+ else
+ return sk->sk_sndbuf;
+}
+
/*
* Compute minimal free write space needed to queue new packets.
*/
static inline int sk_stream_min_wspace(const struct sock *sk)
{
- return sk->sk_wmem_queued >> 1;
+ return sk_wmem_queued_get(sk) >> 1;
}

static inline int sk_stream_wspace(const struct sock *sk)
{
- return sk->sk_sndbuf - sk->sk_wmem_queued;
+ return sk_sndbuf_get(sk) - sk_wmem_queued_get(sk);
}

extern void sk_stream_write_space(struct sock *sk);

static inline bool sk_stream_memory_free(const struct sock *sk)
{
- return sk->sk_wmem_queued < sk->sk_sndbuf;
+ return sk_wmem_queued_get(sk) < sk_sndbuf_get(sk);
}

/* OOB backlog add */
@@ -794,6 +819,7 @@ static inline void sock_rps_reset_rxhash(struct sock *sk)
})

extern int sk_stream_wait_connect(struct sock *sk, long *timeo_p);
+extern int sk_stream_wait_friend(struct sock *sk, long *timeo_p);
extern int sk_stream_wait_memory(struct sock *sk, long *timeo_p);
extern void sk_stream_wait_close(struct sock *sk, long timeo_p);
extern int sk_stream_error(struct sock *sk, int flags, int err);
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 53fb7d8..011ba42 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -253,6 +253,7 @@ extern int sysctl_tcp_cookie_size;
extern int sysctl_tcp_thin_linear_timeouts;
extern int sysctl_tcp_thin_dupack;
extern int sysctl_tcp_early_retrans;
+extern int sysctl_tcp_friends;

extern atomic_long_t tcp_memory_allocated;
extern struct percpu_counter tcp_sockets_allocated;
@@ -978,7 +979,7 @@ static inline bool tcp_prequeue(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);

- if (sysctl_tcp_low_latency || !tp->ucopy.task)
+ if (sysctl_tcp_low_latency || !tp->ucopy.task || sk->sk_friend)
return false;

__skb_queue_tail(&tp->ucopy.prequeue, skb);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 5a789a8..5702145 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -634,6 +634,7 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
#ifdef CONFIG_XFRM
new->sp = secpath_get(old->sp);
#endif
+ new->friend = old->friend;
memcpy(new->cb, old->cb, sizeof(old->cb));
new->csum = old->csum;
new->local_df = old->local_df;
diff --git a/net/core/sock.c b/net/core/sock.c
index 929bdcc..2e4a77d 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2078,6 +2078,7 @@ void sock_init_data(struct socket *sock, struct sock *sk)
#ifdef CONFIG_NET_DMA
skb_queue_head_init(&sk->sk_async_wait_queue);
#endif
+ sk->sk_friend = NULL;

sk->sk_send_head = NULL;

diff --git a/net/core/stream.c b/net/core/stream.c
index f5df85d..85e5b03 100644
--- a/net/core/stream.c
+++ b/net/core/stream.c
@@ -83,6 +83,42 @@ int sk_stream_wait_connect(struct sock *sk, long *timeo_p)
EXPORT_SYMBOL(sk_stream_wait_connect);

/**
+ * sk_stream_wait_friend - Wait for a socket to make friends
+ * @sk: sock to wait on
+ * @timeo_p: for how long to wait
+ *
+ * Must be called with the socket locked.
+ */
+int sk_stream_wait_friend(struct sock *sk, long *timeo_p)
+{
+ struct task_struct *tsk = current;
+ DEFINE_WAIT(wait);
+ int done;
+
+ do {
+ int err = sock_error(sk);
+ if (err)
+ return err;
+ if (!sk->sk_friend)
+ return -EBADFD;
+ if (!*timeo_p)
+ return -EAGAIN;
+ if (signal_pending(tsk))
+ return sock_intr_errno(*timeo_p);
+
+ prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
+ sk->sk_write_pending++;
+ done = sk_wait_event(sk, timeo_p,
+ !sk->sk_err &&
+ sk->sk_friend->sk_friend);
+ finish_wait(sk_sleep(sk), &wait);
+ sk->sk_write_pending--;
+ } while (!done);
+ return 0;
+}
+EXPORT_SYMBOL(sk_stream_wait_friend);
+
+/**
* sk_stream_closing - Return 1 if we still have things to send in our buffers.
* @sk: socket to verify
*/
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 034ddbe..9e16d10 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -626,6 +626,26 @@ struct sock *inet_csk_clone_lock(const struct sock *sk,
if (newsk != NULL) {
struct inet_connection_sock *newicsk = inet_csk(newsk);

+ if (req->friend) {
+ /*
+ * Make friends with the requestor but the ACK of
+ * the request is already in-flight so the race is
+ * on to make friends before the ACK is processed.
+ * If the requestor's sk_friend value is != NULL
+ * then the requestor has already processed the
+ * ACK so indicate state change to wake'm up.
+ */
+ struct sock *was;
+
+ sock_hold(req->friend);
+ newsk->sk_friend = req->friend;
+ sock_hold(newsk);
+ was = xchg(&req->friend->sk_friend, newsk);
+ /* If requester already connect()ed, maybe sleeping */
+ if (was && !sock_flag(req->friend, SOCK_DEAD))
+ sk->sk_state_change(req->friend);
+ }
+
newsk->sk_state = TCP_SYN_RECV;
newicsk->icsk_bind_hash = NULL;

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 12aa0c5..3fc3d50 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -716,6 +716,13 @@ static struct ctl_table ipv4_table[] = {
.proc_handler = proc_dointvec_minmax,
.extra1 = &zero
},
+ {
+ .procname = "tcp_friends",
+ .data = &sysctl_tcp_friends,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec
+ },
{ }
};

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3ba605f..a87f0f5 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -309,6 +309,38 @@ struct tcp_splice_state {
};

/*
+ * Friends? If not a friend return 0, else if friend is also a friend
+ * return 1, else wait for friend to be ready and return 1 if friends
+ * else -errno. In all cases if *friendp != NULL return friend pointer
+ * else NULL.
+ */
+static inline int tcp_friends(struct sock *sk, struct sock **friendp,
+ long *timeo)
+{
+ struct sock *friend = sk->sk_friend;
+ int ret = 0;
+
+ if (!friend)
+ goto out;
+ if (unlikely(!friend->sk_friend)) {
+ /* Friendship not complete, wait? */
+ if (!timeo) {
+ ret = -EAGAIN;
+ goto out;
+ }
+ ret = sk_stream_wait_friend(sk, timeo);
+ if (ret != 0)
+ goto out;
+ friend = sk->sk_friend;
+ }
+ ret = 1;
+out:
+ if (friendp)
+ *friendp = friend;
+ return ret;
+}
+
+/*
* Pressure flag: try to collapse.
* Technical note: it is used by multiple contexts non atomically.
* All the __sk_mem_schedule() is of this nature: accounting
@@ -587,6 +619,73 @@ int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg)
}
EXPORT_SYMBOL(tcp_ioctl);

+static inline struct sk_buff *tcp_friend_tail(struct sock *sk, int *copy)
+{
+ struct sock *friend = sk->sk_friend;
+ struct sk_buff *skb = NULL;
+ int sz = 0;
+
+ if (skb_peek_tail(&friend->sk_receive_queue)) {
+ spin_lock_bh(&friend->sk_lock.slock);
+ skb = skb_peek_tail(&friend->sk_receive_queue);
+ if (skb && skb->friend) {
+ if (!*copy)
+ sz = skb_tailroom(skb);
+ else
+ sz = *copy - skb->len;
+ }
+ if (!skb || sz <= 0)
+ spin_unlock_bh(&friend->sk_lock.slock);
+ }
+
+ *copy = sz;
+ return skb;
+}
+
+static inline void tcp_friend_seq(struct sock *sk, int copy, int charge)
+{
+ struct sock *friend = sk->sk_friend;
+ struct tcp_sock *tp = tcp_sk(friend);
+
+ if (charge) {
+ sk_mem_charge(friend, charge);
+ atomic_add(charge, &friend->sk_rmem_alloc);
+ }
+ tp->rcv_nxt += copy;
+ tp->rcv_wup += copy;
+ spin_unlock_bh(&friend->sk_lock.slock);
+
+ friend->sk_data_ready(friend, copy);
+
+ tp = tcp_sk(sk);
+ tp->snd_nxt += copy;
+ tp->pushed_seq += copy;
+ tp->snd_una += copy;
+ tp->snd_up += copy;
+}
+
+static inline int tcp_friend_push(struct sock *sk, struct sk_buff *skb)
+{
+ struct sock *friend = sk->sk_friend;
+ int ret = 0;
+
+ if (friend->sk_shutdown & RCV_SHUTDOWN) {
+ __kfree_skb(skb);
+ return -ECONNRESET;
+ }
+
+ spin_lock_bh(&friend->sk_lock.slock);
+ skb->friend = sk;
+ skb_set_owner_r(skb, friend);
+ __skb_queue_tail(&friend->sk_receive_queue, skb);
+ if (!sk_rmem_schedule(friend, skb->truesize))
+ ret = 1;
+
+ tcp_friend_seq(sk, skb->len, 0);
+
+ return ret;
+}
+
static inline void tcp_mark_push(struct tcp_sock *tp, struct sk_buff *skb)
{
TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
@@ -603,8 +702,12 @@ static inline void skb_entail(struct sock *sk, struct sk_buff *skb)
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);

- skb->csum = 0;
tcb->seq = tcb->end_seq = tp->write_seq;
+ if (sk->sk_friend) {
+ skb->friend = sk->sk_friend;
+ return;
+ }
+ skb->csum = 0;
tcb->tcp_flags = TCPHDR_ACK;
tcb->sacked = 0;
skb_header_release(skb);
@@ -756,6 +859,21 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
}
EXPORT_SYMBOL(tcp_splice_read);

+static inline struct sk_buff *tcp_friend_alloc_skb(struct sock *sk, int size)
+{
+ struct sk_buff *skb;
+
+ skb = alloc_skb(size, sk->sk_allocation);
+ if (skb)
+ skb->avail_size = skb_tailroom(skb);
+ else {
+ sk->sk_prot->enter_memory_pressure(sk);
+ sk_stream_moderate_sndbuf(sk);
+ }
+
+ return skb;
+}
+
struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp)
{
struct sk_buff *skb;
@@ -813,13 +931,47 @@ static unsigned int tcp_xmit_size_goal(struct sock *sk, u32 mss_now,
return max(xmit_size_goal, mss_now);
}

+static unsigned int tcp_friend_xmit_size_goal(struct sock *sk, int size_goal)
+{
+ u32 tmp = SKB_TRUESIZE(size_goal);
+
+ /*
+ * If goal is zero (for non linear) or truesize of goal >= largest
+ * skb return largest, else for tail fill find smallest order that
+ * fits 8 or more truesized, else use requested truesize.
+ */
+ if (size_goal == 0 || tmp >= SKB_MAX_ORDER(0, 3))
+ tmp = SKB_MAX_ORDER(0, 3);
+ else if (tmp <= (SKB_MAX_ORDER(0, 0) >> 3))
+ tmp = SKB_MAX_ORDER(0, 0);
+ else if (tmp <= (SKB_MAX_ORDER(0, 1) >> 3))
+ tmp = SKB_MAX_ORDER(0, 1);
+ else if (tmp <= (SKB_MAX_ORDER(0, 2) >> 3))
+ tmp = SKB_MAX_ORDER(0, 2);
+ else if (tmp <= (SKB_MAX_ORDER(0, 3) >> 3))
+ tmp = SKB_MAX_ORDER(0, 3);
+
+ /* At least 2 truesized in sk_buf */
+ if (tmp > (sk_sndbuf_get(sk) >> 1))
+ tmp = (sk_sndbuf_get(sk) >> 1) - SKB_TRUESIZE(0);
+
+ return tmp;
+}
+
static int tcp_send_mss(struct sock *sk, int *size_goal, int flags)
{
int mss_now;
+ int tmp;

- mss_now = tcp_current_mss(sk);
- *size_goal = tcp_xmit_size_goal(sk, mss_now, !(flags & MSG_OOB));
+ if (sk->sk_friend) {
+ mss_now = tcp_friend_xmit_size_goal(sk, *size_goal);
+ tmp = mss_now;
+ } else {
+ mss_now = tcp_current_mss(sk);
+ tmp = tcp_xmit_size_goal(sk, mss_now, !(flags & MSG_OOB));
+ }

+ *size_goal = tmp;
return mss_now;
}

@@ -830,6 +982,8 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page **pages, int poffse
int mss_now, size_goal;
int err;
ssize_t copied;
+ struct sock *friend;
+ bool friend_tail = false;
long timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);

/* Wait for a connection to finish. */
@@ -837,6 +991,10 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page **pages, int poffse
if ((err = sk_stream_wait_connect(sk, &timeo)) != 0)
goto out_err;

+ err = tcp_friends(sk, &friend, &timeo);
+ if (err < 0)
+ goto out_err;
+
clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);

mss_now = tcp_send_mss(sk, &size_goal, flags);
@@ -847,19 +1005,40 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page **pages, int poffse
goto out_err;

while (psize > 0) {
- struct sk_buff *skb = tcp_write_queue_tail(sk);
+ struct sk_buff *skb;
struct page *page = pages[poffset / PAGE_SIZE];
int copy, i;
int offset = poffset % PAGE_SIZE;
int size = min_t(size_t, psize, PAGE_SIZE - offset);
bool can_coalesce;

- if (!tcp_send_head(sk) || (copy = size_goal - skb->len) <= 0) {
+ if (sk->sk_friend) {
+ if (sk->sk_friend->sk_shutdown & RCV_SHUTDOWN) {
+ sk->sk_err = ECONNRESET;
+ err = -EPIPE;
+ goto out_err;
+ }
+ copy = size_goal;
+ skb = tcp_friend_tail(sk, &copy);
+ if (copy > 0)
+ friend_tail = true;
+ } else if (!tcp_send_head(sk)) {
+ copy = 0;
+ } else {
+ skb = tcp_write_queue_tail(sk);
+ copy = size_goal - skb->len;
+ }
+
+ if (copy <= 0) {
new_segment:
if (!sk_stream_memory_free(sk))
goto wait_for_sndbuf;

- skb = sk_stream_alloc_skb(sk, 0, sk->sk_allocation);
+ if (sk->sk_friend)
+ skb = tcp_friend_alloc_skb(sk, 0);
+ else
+ skb = sk_stream_alloc_skb(sk, 0,
+ sk->sk_allocation);
if (!skb)
goto wait_for_memory;

@@ -873,10 +1052,16 @@ new_segment:
i = skb_shinfo(skb)->nr_frags;
can_coalesce = skb_can_coalesce(skb, i, page, offset);
if (!can_coalesce && i >= MAX_SKB_FRAGS) {
- tcp_mark_push(tp, skb);
+ if (friend) {
+ if (friend_tail) {
+ tcp_friend_seq(sk, 0, 0);
+ friend_tail = false;
+ }
+ } else
+ tcp_mark_push(tp, skb);
goto new_segment;
}
- if (!sk_wmem_schedule(sk, copy))
+ if (!friend && !sk_wmem_schedule(sk, copy))
goto wait_for_memory;

if (can_coalesce) {
@@ -889,19 +1074,40 @@ new_segment:
skb->len += copy;
skb->data_len += copy;
skb->truesize += copy;
- sk->sk_wmem_queued += copy;
- sk_mem_charge(sk, copy);
- skb->ip_summed = CHECKSUM_PARTIAL;
tp->write_seq += copy;
TCP_SKB_CB(skb)->end_seq += copy;
skb_shinfo(skb)->gso_segs = 0;

- if (!copied)
- TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
-
copied += copy;
poffset += copy;
- if (!(psize -= copy))
+ psize -= copy;
+
+ if (friend) {
+ if (friend_tail) {
+ tcp_friend_seq(sk, copy, copy);
+ friend_tail = false;
+ } else {
+ err = tcp_friend_push(sk, skb);
+ if (err < 0) {
+ sk->sk_err = -err;
+ goto out_err;
+ }
+ if (err > 0)
+ goto wait_for_sndbuf;
+ }
+ if (!psize)
+ goto out;
+ continue;
+ }
+
+ sk->sk_wmem_queued += copy;
+ sk_mem_charge(sk, copy);
+ skb->ip_summed = CHECKSUM_PARTIAL;
+
+ if (copied == copy)
+ TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
+
+ if (!psize)
goto out;

if (skb->len < size_goal || (flags & MSG_OOB))
@@ -922,6 +1128,7 @@ wait_for_memory:
if ((err = sk_stream_wait_memory(sk, &timeo)) != 0)
goto do_error;

+ size_goal = -mss_now;
mss_now = tcp_send_mss(sk, &size_goal, flags);
}

@@ -984,8 +1191,9 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
int iovlen, flags, err, copied;
- int mss_now = 0, size_goal;
- bool sg;
+ int mss_now = 0, size_goal = size;
+ struct sock *friend;
+ bool sg, friend_tail = false;
long timeo;

lock_sock(sk);
@@ -998,6 +1206,10 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
if ((err = sk_stream_wait_connect(sk, &timeo)) != 0)
goto out_err;

+ err = tcp_friends(sk, &friend, &timeo);
+ if (err < 0)
+ goto out_err;
+
if (unlikely(tp->repair)) {
if (tp->repair_queue == TCP_RECV_QUEUE) {
copied = tcp_send_rcvq(sk, msg, size);
@@ -1037,24 +1249,40 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
int copy = 0;
int max = size_goal;

- skb = tcp_write_queue_tail(sk);
- if (tcp_send_head(sk)) {
- if (skb->ip_summed == CHECKSUM_NONE)
- max = mss_now;
- copy = max - skb->len;
+ if (friend) {
+ if (friend->sk_shutdown & RCV_SHUTDOWN) {
+ sk->sk_err = ECONNRESET;
+ err = -EPIPE;
+ goto out_err;
+ }
+ skb = tcp_friend_tail(sk, &copy);
+ if (copy)
+ friend_tail = true;
+ } else {
+ skb = tcp_write_queue_tail(sk);
+ if (tcp_send_head(sk)) {
+ if (skb->ip_summed == CHECKSUM_NONE)
+ max = mss_now;
+ copy = max - skb->len;
+ }
}

if (copy <= 0) {
new_segment:
- /* Allocate new segment. If the interface is SG,
- * allocate skb fitting to single page.
- */
if (!sk_stream_memory_free(sk))
goto wait_for_sndbuf;

- skb = sk_stream_alloc_skb(sk,
- select_size(sk, sg),
- sk->sk_allocation);
+ if (friend)
+ skb = tcp_friend_alloc_skb(sk, max);
+ else {
+ /* Allocate new segment. If the
+ * interface is SG, allocate skb
+ * fitting to single page.
+ */
+ skb = sk_stream_alloc_skb(sk,
+ select_size(sk, sg),
+ sk->sk_allocation);
+ }
if (!skb)
goto wait_for_memory;

@@ -1086,6 +1314,8 @@ new_segment:
struct page *page = sk->sk_sndmsg_page;
int off;

+ BUG_ON(friend);
+
if (page && page_count(page) == 1)
sk->sk_sndmsg_off = 0;

@@ -1155,16 +1385,34 @@ new_segment:
sk->sk_sndmsg_off = off + copy;
}

- if (!copied)
- TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
-
tp->write_seq += copy;
TCP_SKB_CB(skb)->end_seq += copy;
skb_shinfo(skb)->gso_segs = 0;

from += copy;
copied += copy;
- if ((seglen -= copy) == 0 && iovlen == 0)
+ seglen -= copy;
+
+ if (friend) {
+ if (friend_tail) {
+ tcp_friend_seq(sk, copy, 0);
+ friend_tail = false;
+ } else {
+ err = tcp_friend_push(sk, skb);
+ if (err < 0) {
+ sk->sk_err = -err;
+ goto out_err;
+ }
+ if (err > 0)
+ goto wait_for_sndbuf;
+ }
+ continue;
+ }
+
+ if (copied == copy)
+ TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
+
+ if (seglen == 0 && iovlen == 0)
goto out;

if (skb->len < max || (flags & MSG_OOB) || unlikely(tp->repair))
@@ -1186,6 +1434,7 @@ wait_for_memory:
if ((err = sk_stream_wait_memory(sk, &timeo)) != 0)
goto do_error;

+ size_goal = -mss_now;
mss_now = tcp_send_mss(sk, &size_goal, flags);
}
}
@@ -1197,13 +1446,19 @@ out:
return copied;

do_fault:
- if (!skb->len) {
- tcp_unlink_write_queue(skb, sk);
- /* It is the one place in all of TCP, except connection
- * reset, where we can be unlinking the send_head.
- */
- tcp_check_send_head(sk, skb);
- sk_wmem_free_skb(sk, skb);
+ if (friend_tail)
+ spin_unlock_bh(&friend->sk_lock.slock);
+ else if (!skb->len) {
+ if (friend) {
+ __kfree_skb(skb);
+ } else {
+ tcp_unlink_write_queue(skb, sk);
+ /* It is the one place in all of TCP, except connection
+ * reset, where we can be unlinking the send_head.
+ */
+ tcp_check_send_head(sk, skb);
+ sk_wmem_free_skb(sk, skb);
+ }
}

do_error:
@@ -1216,6 +1471,13 @@ out_err:
}
EXPORT_SYMBOL(tcp_sendmsg);

+static inline void tcp_friend_write_space(struct sock *sk)
+{
+ /* Queued data below 1/4th of sndbuf? */
+ if ((sk_sndbuf_get(sk) >> 2) > sk_wmem_queued_get(sk))
+ sk->sk_friend->sk_write_space(sk->sk_friend);
+}
+
/*
* Handle reading urgent data. BSD has very simple semantics for
* this, no blocking and very strange errors 8)
@@ -1294,7 +1556,12 @@ void tcp_cleanup_rbuf(struct sock *sk, int copied)
struct tcp_sock *tp = tcp_sk(sk);
bool time_to_ack = false;

- struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
+ struct sk_buff *skb;
+
+ if (sk->sk_friend)
+ return;
+
+ skb = skb_peek(&sk->sk_receive_queue);

WARN(skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq),
"cleanup rbuf bug: copied %X seq %X rcvnxt %X\n",
@@ -1405,9 +1672,9 @@ static inline struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)

skb_queue_walk(&sk->sk_receive_queue, skb) {
offset = seq - TCP_SKB_CB(skb)->seq;
- if (tcp_hdr(skb)->syn)
+ if (!skb->friend && tcp_hdr(skb)->syn)
offset--;
- if (offset < skb->len || tcp_hdr(skb)->fin) {
+ if (offset < skb->len || (!skb->friend && tcp_hdr(skb)->fin)) {
*off = offset;
return skb;
}
@@ -1434,14 +1701,27 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
u32 seq = tp->copied_seq;
u32 offset;
int copied = 0;
+ struct sock *friend = sk->sk_friend;

if (sk->sk_state == TCP_LISTEN)
return -ENOTCONN;
+
+ if (friend) {
+ int err;
+ long timeo = sock_rcvtimeo(sk, false);
+
+ err = tcp_friends(sk, &friend, &timeo);
+ if (err < 0)
+ return err;
+ spin_lock_bh(&sk->sk_lock.slock);
+ }
+
while ((skb = tcp_recv_skb(sk, seq, &offset)) != NULL) {
if (offset < skb->len) {
int used;
size_t len;

+ again:
len = skb->len - offset;
/* Stop reading if we hit a patch of urgent data */
if (tp->urg_data) {
@@ -1451,7 +1731,13 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
if (!len)
break;
}
+ if (sk->sk_friend)
+ spin_unlock_bh(&sk->sk_lock.slock);
+
used = recv_actor(desc, skb, offset, len);
+
+ if (sk->sk_friend)
+ spin_lock_bh(&sk->sk_lock.slock);
if (used < 0) {
if (!copied)
copied = used;
@@ -1461,17 +1747,31 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
copied += used;
offset += used;
}
- /*
- * If recv_actor drops the lock (e.g. TCP splice
- * receive) the skb pointer might be invalid when
- * getting here: tcp_collapse might have deleted it
- * while aggregating skbs from the socket queue.
- */
- skb = tcp_recv_skb(sk, seq-1, &offset);
- if (!skb || (offset+1 != skb->len))
- break;
+ if (skb->friend) {
+ if (offset < skb->len) {
+ /*
+ * Friend did an skb_put() while we
+ * were away so process the same skb.
+ */
+ tp->copied_seq = seq;
+ if (!desc->count)
+ break;
+ goto again;
+ }
+ } else {
+ /*
+ * If recv_actor drops the lock (e.g. TCP
+ * splice receive) the skb pointer might be
+ * invalid when getting here: tcp_collapse
+ * might have deleted it while aggregating
+ * skbs from the socket queue.
+ */
+ skb = tcp_recv_skb(sk, seq-1, &offset);
+ if (!skb || (offset+1 != skb->len))
+ break;
+ }
}
- if (tcp_hdr(skb)->fin) {
+ if (!skb->friend && tcp_hdr(skb)->fin) {
sk_eat_skb(sk, skb, false);
++seq;
break;
@@ -1483,11 +1783,16 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
}
tp->copied_seq = seq;

- tcp_rcv_space_adjust(sk);
+ if (sk->sk_friend) {
+ spin_unlock_bh(&sk->sk_lock.slock);
+ tcp_friend_write_space(sk);
+ } else {
+ tcp_rcv_space_adjust(sk);

- /* Clean up data we have read: This will do ACK frames. */
- if (copied > 0)
- tcp_cleanup_rbuf(sk, copied);
+ /* Clean up data we have read: This will do ACK frames. */
+ if (copied > 0)
+ tcp_cleanup_rbuf(sk, copied);
+ }
return copied;
}
EXPORT_SYMBOL(tcp_read_sock);
@@ -1515,6 +1820,9 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
bool copied_early = false;
struct sk_buff *skb;
u32 urg_hole = 0;
+ int skb_len;
+ struct sock *friend;
+ bool locked = false;

lock_sock(sk);

@@ -1524,6 +1832,10 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,

timeo = sock_rcvtimeo(sk, nonblock);

+ err = tcp_friends(sk, &friend, &timeo);
+ if (err < 0)
+ goto out;
+
/* Urgent data needs to be handled specially. */
if (flags & MSG_OOB)
goto recv_urg;
@@ -1562,7 +1874,7 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
available = TCP_SKB_CB(skb)->seq + skb->len - (*seq);
if ((available < target) &&
(len > sysctl_tcp_dma_copybreak) && !(flags & MSG_PEEK) &&
- !sysctl_tcp_low_latency &&
+ !sysctl_tcp_low_latency && !friends &&
net_dma_find_channel()) {
preempt_enable_no_resched();
tp->ucopy.pinned_list =
@@ -1586,9 +1898,30 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
}
}

- /* Next get a buffer. */
+ /*
+ * Next get a buffer. Note, for socket friends a sk_friend
+ * sendmsg() can either skb_queue_tail() a new skb directly
+ * or skb_put() to the tail skb while holding sk_lock.slock.
+ */
+ if (friend && !locked) {
+ spin_lock_bh(&sk->sk_lock.slock);
+ locked = true;
+ }

skb_queue_walk(&sk->sk_receive_queue, skb) {
+ offset = *seq - TCP_SKB_CB(skb)->seq;
+ skb_len = skb->len;
+ if (friend) {
+ spin_unlock_bh(&sk->sk_lock.slock);
+ locked = false;
+ if (skb->friend) {
+ if (offset < skb_len)
+ goto found_ok_skb;
+ BUG_ON(!(flags & MSG_PEEK));
+ break;
+ }
+ }
+
/* Now that we have two receive queues this
* shouldn't happen.
*/
@@ -1598,10 +1931,9 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
flags))
break;

- offset = *seq - TCP_SKB_CB(skb)->seq;
if (tcp_hdr(skb)->syn)
offset--;
- if (offset < skb->len)
+ if (offset < skb_len)
goto found_ok_skb;
if (tcp_hdr(skb)->fin)
goto found_fin_ok;
@@ -1612,6 +1944,11 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,

/* Well, if we have backlog, try to process it now yet. */

+ if (friend && locked) {
+ spin_unlock_bh(&sk->sk_lock.slock);
+ locked = false;
+ }
+
if (copied >= target && !sk->sk_backlog.tail)
break;

@@ -1658,7 +1995,8 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,

tcp_cleanup_rbuf(sk, copied);

- if (!sysctl_tcp_low_latency && tp->ucopy.task == user_recv) {
+ if (!sysctl_tcp_low_latency && !friend &&
+ tp->ucopy.task == user_recv) {
/* Install new reader */
if (!user_recv && !(flags & (MSG_TRUNC | MSG_PEEK))) {
user_recv = current;
@@ -1753,7 +2091,7 @@ do_prequeue:

found_ok_skb:
/* Ok so how much can we use? */
- used = skb->len - offset;
+ used = skb_len - offset;
if (len < used)
used = len;

@@ -1799,7 +2137,7 @@ do_prequeue:

dma_async_memcpy_issue_pending(tp->ucopy.dma_chan);

- if ((offset + used) == skb->len)
+ if ((offset + used) == skb_len)
copied_early = true;

} else
@@ -1819,6 +2157,7 @@ do_prequeue:
*seq += used;
copied += used;
len -= used;
+ offset += used;

tcp_rcv_space_adjust(sk);

@@ -1827,11 +2166,36 @@ skip_copy:
tp->urg_data = 0;
tcp_fast_path_check(sk);
}
- if (used + offset < skb->len)
+
+ if (friend) {
+ spin_lock_bh(&sk->sk_lock.slock);
+ locked = true;
+ skb_len = skb->len;
+ if (offset < skb_len) {
+ if (skb->friend && len > 0) {
+ /*
+ * Friend did an skb_put() while we
+ * were away so process the same skb.
+ */
+ spin_unlock_bh(&sk->sk_lock.slock);
+ locked = false;
+ goto found_ok_skb;
+ }
+ continue;
+ }
+ if (!(flags & MSG_PEEK)) {
+ __skb_unlink(skb, &sk->sk_receive_queue);
+ __kfree_skb(skb);
+ tcp_friend_write_space(sk);
+ }
continue;
+ }

- if (tcp_hdr(skb)->fin)
+ if (offset < skb_len)
+ continue;
+ else if (tcp_hdr(skb)->fin)
goto found_fin_ok;
+
if (!(flags & MSG_PEEK)) {
sk_eat_skb(sk, skb, copied_early);
copied_early = false;
@@ -1848,6 +2212,9 @@ skip_copy:
break;
} while (len > 0);

+ if (friend && locked)
+ spin_unlock_bh(&sk->sk_lock.slock);
+
if (user_recv) {
if (!skb_queue_empty(&tp->ucopy.prequeue)) {
int chunk;
@@ -2026,6 +2393,9 @@ void tcp_close(struct sock *sk, long timeout)
goto adjudge_to_death;
}

+ if (sk->sk_friend)
+ sock_put(sk->sk_friend);
+
/* We need to flush the recv. buffs. We do this only on the
* descriptor close, not protocol-sourced closes, because the
* reader process may not have drained the data yet!
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index ca0d0e7..d31a8d5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -524,6 +524,9 @@ void tcp_rcv_space_adjust(struct sock *sk)
int time;
int space;

+ if (sk->sk_friend)
+ return;
+
if (tp->rcvq_space.time == 0)
goto new_measure;

@@ -4516,8 +4519,9 @@ static int tcp_prune_queue(struct sock *sk);

static int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
{
- if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
- !sk_rmem_schedule(sk, size)) {
+ if (!sk->sk_friend &&
+ (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
+ !sk_rmem_schedule(sk, size))) {

if (tcp_prune_queue(sk) < 0)
return -1;
@@ -5839,6 +5843,16 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
* state to ESTABLISHED..."
*/

+ if (skb->friend) {
+ /*
+ * If friends haven't been made yet, our sk_friend
+ * still == NULL, then update with the ACK's friend
+ * value (the listen()er's sock addr) which is used
+ * as a place holder.
+ */
+ cmpxchg(&sk->sk_friend, NULL, skb->friend);
+ }
+
TCP_ECN_rcv_synack(tp, th);

tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
@@ -5911,9 +5925,9 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,

tcp_finish_connect(sk, skb);

- if (sk->sk_write_pending ||
+ if (!skb->friend && (sk->sk_write_pending ||
icsk->icsk_accept_queue.rskq_defer_accept ||
- icsk->icsk_ack.pingpong) {
+ icsk->icsk_ack.pingpong)) {
/* Save one ACK. Data will be ready after
* several ticks, if write_pending is set.
*
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 64568fa..45ccafd 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1314,6 +1314,8 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
tcp_rsk(req)->af_specific = &tcp_request_sock_ipv4_ops;
#endif

+ req->friend = skb->friend;
+
tcp_clear_options(&tmp_opt);
tmp_opt.mss_clamp = TCP_MSS_DEFAULT;
tmp_opt.user_mss = tp->rx_opt.user_mss;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 72b7c63..4ff285b 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -315,6 +315,11 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
bool recycle_ok = false;
bool recycle_on = false;

+ if (sk->sk_friend) {
+ tcp_done(sk);
+ return;
+ }
+
if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp) {
recycle_ok = tcp_remember_stamp(sk);
recycle_on = true;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c465d3e..542b34a 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -65,6 +65,9 @@ int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
int sysctl_tcp_cookie_size __read_mostly = 0; /* TCP_COOKIE_MAX */
EXPORT_SYMBOL_GPL(sysctl_tcp_cookie_size);

+/* TCP loopback bypass */
+int sysctl_tcp_friends __read_mostly = 1;
+

/* Account for new data that has been sent to the network. */
static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
@@ -829,9 +832,14 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
tcb = TCP_SKB_CB(skb);
memset(&opts, 0, sizeof(opts));

- if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
+ if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
+ if (sysctl_tcp_friends) {
+ /* Only try to make friends if enabled */
+ skb->friend = sk;
+ }
+
tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
- else
+ } else
tcp_options_size = tcp_established_options(sk, skb, &opts,
&md5);
tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
@@ -2506,6 +2514,12 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
}

memset(&opts, 0, sizeof(opts));
+
+ if (sysctl_tcp_friends) {
+ /* Only try to make friends if enabled */
+ skb->friend = sk;
+ }
+
#ifdef CONFIG_SYN_COOKIES
if (unlikely(req->cookie_ts))
TCP_SKB_CB(skb)->when = cookie_init_timestamp(req);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 6cc67ed..33f9d47 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1066,6 +1066,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
tcp_rsk(req)->af_specific = &tcp_request_sock_ipv6_ops;
#endif

+ req->friend = skb->friend;
tcp_clear_options(&tmp_opt);
tmp_opt.mss_clamp = IPV6_MIN_MTU - sizeof(struct tcphdr) - sizeof(struct ipv6hdr);
tmp_opt.user_mss = tp->rx_opt.user_mss;
--
1.7.7.3