Merge branch 'tcp-zero-copy-receive'

Eric Dumazet says:

====================
tcp: add zero copy receive

This patch series add mmap() support to TCP sockets for RX zero copy.

While tcp_mmap() patch itself is quite small (~100 LOC), optimal support
for asynchronous mmap() required better SO_RCVLOWAT behavior, and a
test program to demonstrate how mmap() on TCP sockets can be used.

Note that mmap() (and associated munmap()) calls are adding more
pressure on per-process VM semaphore, so might not show benefit
for processus with high number of threads.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/net.h

@@ -197,6 +197,7 @@ struct proto_ops {
 					   int offset, size_t size, int flags);
 	int		(*sendmsg_locked)(struct sock *sk, struct msghdr *msg,
 					  size_t size);
+	int		(*set_rcvlowat)(struct sock *sk, int val);
 };
 
 #define DECLARE_SOCKADDR(type, dst, src)	\

include/net/tcp.h

@@ -402,6 +402,10 @@ void tcp_set_keepalive(struct sock *sk, int val);
 void tcp_syn_ack_timeout(const struct request_sock *req);
 int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
 		int flags, int *addr_len);
+int tcp_set_rcvlowat(struct sock *sk, int val);
+void tcp_data_ready(struct sock *sk);
+int tcp_mmap(struct file *file, struct socket *sock,
+	     struct vm_area_struct *vma);
 void tcp_parse_options(const struct net *net, const struct sk_buff *skb,
 		       struct tcp_options_received *opt_rx,
 		       int estab, struct tcp_fastopen_cookie *foc);

net/core/sock.c

@@ -905,7 +905,10 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 	case SO_RCVLOWAT:
 		if (val < 0)
 			val = INT_MAX;
-		sk->sk_rcvlowat = val ? : 1;
+		if (sock->ops->set_rcvlowat)
+			ret = sock->ops->set_rcvlowat(sk, val);
+		else
+			sk->sk_rcvlowat = val ? : 1;
 		break;
 
 	case SO_RCVTIMEO:

net/ipv4/af_inet.c

@@ -994,7 +994,7 @@ const struct proto_ops inet_stream_ops = {
 	.getsockopt	   = sock_common_getsockopt,
 	.sendmsg	   = inet_sendmsg,
 	.recvmsg	   = inet_recvmsg,
-	.mmap		   = sock_no_mmap,
+	.mmap		   = tcp_mmap,
 	.sendpage	   = inet_sendpage,
 	.splice_read	   = tcp_splice_read,
 	.read_sock	   = tcp_read_sock,
@@ -1006,6 +1006,7 @@ const struct proto_ops inet_stream_ops = {
 	.compat_getsockopt = compat_sock_common_getsockopt,
 	.compat_ioctl	   = inet_compat_ioctl,
 #endif
+	.set_rcvlowat	   = tcp_set_rcvlowat,
 };
 EXPORT_SYMBOL(inet_stream_ops);
 

net/ipv4/tcp.c

@@ -1701,6 +1701,144 @@ int tcp_peek_len(struct socket *sock)
 }
 EXPORT_SYMBOL(tcp_peek_len);
 
+/* Make sure sk_rcvbuf is big enough to satisfy SO_RCVLOWAT hint */
+int tcp_set_rcvlowat(struct sock *sk, int val)
+{
+	sk->sk_rcvlowat = val ? : 1;
+
+	/* Check if we need to signal EPOLLIN right now */
+	tcp_data_ready(sk);
+
+	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK)
+		return 0;
+
+	/* val comes from user space and might be close to INT_MAX */
+	val <<= 1;
+	if (val < 0)
+		val = INT_MAX;
+
+	val = min(val, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
+	if (val > sk->sk_rcvbuf) {
+		sk->sk_rcvbuf = val;
+		tcp_sk(sk)->window_clamp = tcp_win_from_space(sk, val);
+	}
+	return 0;
+}
+EXPORT_SYMBOL(tcp_set_rcvlowat);
+
+/* When user wants to mmap X pages, we first need to perform the mapping
+ * before freeing any skbs in receive queue, otherwise user would be unable
+ * to fallback to standard recvmsg(). This happens if some data in the
+ * requested block is not exactly fitting in a page.
+ *
+ * We only support order-0 pages for the moment.
+ * mmap() on TCP is very strict, there is no point
+ * trying to accommodate with pathological layouts.
+ */
+int tcp_mmap(struct file *file, struct socket *sock,
+	     struct vm_area_struct *vma)
+{
+	unsigned long size = vma->vm_end - vma->vm_start;
+	unsigned int nr_pages = size >> PAGE_SHIFT;
+	struct page **pages_array = NULL;
+	u32 seq, len, offset, nr = 0;
+	struct sock *sk = sock->sk;
+	const skb_frag_t *frags;
+	struct tcp_sock *tp;
+	struct sk_buff *skb;
+	int ret;
+
+	if (vma->vm_pgoff || !nr_pages)
+		return -EINVAL;
+
+	if (vma->vm_flags & VM_WRITE)
+		return -EPERM;
+	/* TODO: Maybe the following is not needed if pages are COW */
+	vma->vm_flags &= ~VM_MAYWRITE;
+
+	lock_sock(sk);
+
+	ret = -ENOTCONN;
+	if (sk->sk_state == TCP_LISTEN)
+		goto out;
+
+	sock_rps_record_flow(sk);
+
+	if (tcp_inq(sk) < size) {
+		ret = sock_flag(sk, SOCK_DONE) ? -EIO : -EAGAIN;
+		goto out;
+	}
+	tp = tcp_sk(sk);
+	seq = tp->copied_seq;
+	/* Abort if urgent data is in the area */
+	if (unlikely(tp->urg_data)) {
+		u32 urg_offset = tp->urg_seq - seq;
+
+		ret = -EINVAL;
+		if (urg_offset < size)
+			goto out;
+	}
+	ret = -ENOMEM;
+	pages_array = kvmalloc_array(nr_pages, sizeof(struct page *),
+				     GFP_KERNEL);
+	if (!pages_array)
+		goto out;
+	skb = tcp_recv_skb(sk, seq, &offset);
+	ret = -EINVAL;
+skb_start:
+	/* We do not support anything not in page frags */
+	offset -= skb_headlen(skb);
+	if ((int)offset < 0)
+		goto out;
+	if (skb_has_frag_list(skb))
+		goto out;
+	len = skb->data_len - offset;
+	frags = skb_shinfo(skb)->frags;
+	while (offset) {
+		if (frags->size > offset)
+			goto out;
+		offset -= frags->size;
+		frags++;
+	}
+	while (nr < nr_pages) {
+		if (len) {
+			if (len < PAGE_SIZE)
+				goto out;
+			if (frags->size != PAGE_SIZE || frags->page_offset)
+				goto out;
+			pages_array[nr++] = skb_frag_page(frags);
+			frags++;
+			len -= PAGE_SIZE;
+			seq += PAGE_SIZE;
+			continue;
+		}
+		skb = skb->next;
+		offset = seq - TCP_SKB_CB(skb)->seq;
+		goto skb_start;
+	}
+	/* OK, we have a full set of pages ready to be inserted into vma */
+	for (nr = 0; nr < nr_pages; nr++) {
+		ret = vm_insert_page(vma, vma->vm_start + (nr << PAGE_SHIFT),
+				     pages_array[nr]);
+		if (ret)
+			goto out;
+	}
+	/* operation is complete, we can 'consume' all skbs */
+	tp->copied_seq = seq;
+	tcp_rcv_space_adjust(sk);
+
+	/* Clean up data we have read: This will do ACK frames. */
+	tcp_recv_skb(sk, seq, &offset);
+	tcp_cleanup_rbuf(sk, size);
+
+	ret = 0;
+out:
+	release_sock(sk);
+	kvfree(pages_array);
+	return ret;
+}
+EXPORT_SYMBOL(tcp_mmap);
+
 static void tcp_update_recv_tstamps(struct sk_buff *skb,
 				    struct scm_timestamping *tss)
 {

net/ipv4/tcp_input.c

@@ -4576,6 +4576,17 @@ int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
 
 }
 
+void tcp_data_ready(struct sock *sk)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+	int avail = tp->rcv_nxt - tp->copied_seq;
+
+	if (avail < sk->sk_rcvlowat && !sock_flag(sk, SOCK_DONE))
+		return;
+
+	sk->sk_data_ready(sk);
+}
+
 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -4633,7 +4644,7 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
 		if (eaten > 0)
 			kfree_skb_partial(skb, fragstolen);
 		if (!sock_flag(sk, SOCK_DEAD))
-			sk->sk_data_ready(sk);
+			tcp_data_ready(sk);
 		return;
 	}
 
@@ -5026,9 +5037,12 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
 	    /* More than one full frame received... */
 	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
 	     /* ... and right edge of window advances far enough.
-	      * (tcp_recvmsg() will send ACK otherwise). Or...
+	      * (tcp_recvmsg() will send ACK otherwise).
+	      * If application uses SO_RCVLOWAT, we want send ack now if
+	      * we have not received enough bytes to satisfy the condition.
 	      */
-	     __tcp_select_window(sk) >= tp->rcv_wnd) ||
+	    (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
+	     __tcp_select_window(sk) >= tp->rcv_wnd)) ||
 	    /* We ACK each frame or... */
 	    tcp_in_quickack_mode(sk) ||
 	    /* We have out of order data. */
@@ -5431,7 +5445,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 no_ack:
 			if (eaten)
 				kfree_skb_partial(skb, fragstolen);
-			sk->sk_data_ready(sk);
+			tcp_data_ready(sk);
 			return;
 		}
 	}

net/ipv6/af_inet6.c

@@ -579,7 +579,7 @@ const struct proto_ops inet6_stream_ops = {
 	.getsockopt	   = sock_common_getsockopt,	/* ok		*/
 	.sendmsg	   = inet_sendmsg,		/* ok		*/
 	.recvmsg	   = inet_recvmsg,		/* ok		*/
-	.mmap		   = sock_no_mmap,
+	.mmap		   = tcp_mmap,
 	.sendpage	   = inet_sendpage,
 	.sendmsg_locked    = tcp_sendmsg_locked,
 	.sendpage_locked   = tcp_sendpage_locked,
@@ -590,6 +590,7 @@ const struct proto_ops inet6_stream_ops = {
 	.compat_setsockopt = compat_sock_common_setsockopt,
 	.compat_getsockopt = compat_sock_common_getsockopt,
 #endif
+	.set_rcvlowat	   = tcp_set_rcvlowat,
 };
 
 const struct proto_ops inet6_dgram_ops = {

tools/testing/selftests/net/Makefile

@@ -8,9 +8,11 @@ TEST_PROGS := run_netsocktests run_afpackettests test_bpf.sh netdevice.sh rtnetl
 TEST_PROGS += fib_tests.sh fib-onlink-tests.sh pmtu.sh
 TEST_GEN_FILES =  socket
 TEST_GEN_FILES += psock_fanout psock_tpacket msg_zerocopy
+TEST_GEN_FILES += tcp_mmap
 TEST_GEN_PROGS = reuseport_bpf reuseport_bpf_cpu reuseport_bpf_numa
 TEST_GEN_PROGS += reuseport_dualstack reuseaddr_conflict
 
 include ../lib.mk
 
 $(OUTPUT)/reuseport_bpf_numa: LDFLAGS += -lnuma
+$(OUTPUT)/tcp_mmap: LDFLAGS += -lpthread

tools/testing/selftests/net/tcp_mmap.c

+/*
+ * Copyright 2018 Google Inc.
+ * Author: Eric Dumazet (edumazet@google.com)
+ *
+ * Reference program demonstrating tcp mmap() usage,
+ * and SO_RCVLOWAT hints for receiver.
+ *
+ * Note : NIC with header split is needed to use mmap() on TCP :
+ * Each incoming frame must be a multiple of PAGE_SIZE bytes of TCP payload.
+ *
+ * How to use on loopback interface :
+ *
+ *  ifconfig lo mtu 61512  # 15*4096 + 40 (ipv6 header) + 32 (TCP with TS option header)
+ *  tcp_mmap -s -z &
+ *  tcp_mmap -H ::1 -z
+ *
+ *  Or leave default lo mtu, but use -M option to set TCP_MAXSEG option to (4096 + 12)
+ *      (4096 : page size on x86, 12: TCP TS option length)
+ *  tcp_mmap -s -z -M $((4096+12)) &
+ *  tcp_mmap -H ::1 -z -M $((4096+12))
+ *
+ * Note: -z option on sender uses MSG_ZEROCOPY, which forces a copy when packets go through loopback interface.
+ *       We might use sendfile() instead, but really this test program is about mmap(), for receivers ;)
+ *
+ * $ ./tcp_mmap -s &                                 # Without mmap()
+ * $ for i in {1..4}; do ./tcp_mmap -H ::1 -z ; done
+ * received 32768 MB (0 % mmap'ed) in 14.1157 s, 19.4732 Gbit
+ *   cpu usage user:0.057 sys:7.815, 240.234 usec per MB, 65531 c-switches
+ * received 32768 MB (0 % mmap'ed) in 14.6833 s, 18.7204 Gbit
+ *  cpu usage user:0.043 sys:8.103, 248.596 usec per MB, 65524 c-switches
+ * received 32768 MB (0 % mmap'ed) in 11.143 s, 24.6682 Gbit
+ *   cpu usage user:0.044 sys:6.576, 202.026 usec per MB, 65519 c-switches
+ * received 32768 MB (0 % mmap'ed) in 14.9056 s, 18.4413 Gbit
+ *   cpu usage user:0.036 sys:8.193, 251.129 usec per MB, 65530 c-switches
+ * $ kill %1   # kill tcp_mmap server
+ *
+ * $ ./tcp_mmap -s -z &                              # With mmap()
+ * $ for i in {1..4}; do ./tcp_mmap -H ::1 -z ; done
+ * received 32768 MB (99.9939 % mmap'ed) in 6.73792 s, 40.7956 Gbit
+ *   cpu usage user:0.045 sys:2.827, 87.6465 usec per MB, 65532 c-switches
+ * received 32768 MB (99.9939 % mmap'ed) in 7.26732 s, 37.8238 Gbit
+ *   cpu usage user:0.037 sys:3.087, 95.3369 usec per MB, 65532 c-switches
+ * received 32768 MB (99.9939 % mmap'ed) in 7.61661 s, 36.0893 Gbit
+ *   cpu usage user:0.046 sys:3.559, 110.016 usec per MB, 65529 c-switches
+ * received 32768 MB (99.9939 % mmap'ed) in 7.43764 s, 36.9577 Gbit
+ *   cpu usage user:0.035 sys:3.467, 106.873 usec per MB, 65530 c-switches
+ *
+ * License (GPLv2):
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. * See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+#define _GNU_SOURCE
+#include <pthread.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <error.h>
+#include <sys/socket.h>
+#include <sys/mman.h>
+#include <sys/resource.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <time.h>
+#include <sys/time.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <arpa/inet.h>
+#include <poll.h>
+
+#ifndef MSG_ZEROCOPY
+#define MSG_ZEROCOPY    0x4000000
+#endif
+
+#define FILE_SZ (1UL << 35)
+static int cfg_family = AF_INET6;
+static socklen_t cfg_alen = sizeof(struct sockaddr_in6);
+static int cfg_port = 8787;
+
+static int rcvbuf; /* Default: autotuning.  Can be set with -r <integer> option */
+static int sndbuf; /* Default: autotuning.  Can be set with -w <integer> option */
+static int zflg; /* zero copy option. (MSG_ZEROCOPY for sender, mmap() for receiver */
+static int xflg; /* hash received data (simple xor) (-h option) */
+static int keepflag; /* -k option: receiver shall keep all received file in memory (no munmap() calls) */
+
+static int chunk_size  = 512*1024;
+
+unsigned long htotal;
+
+static inline void prefetch(const void *x)
+{
+#if defined(__x86_64__)
+	asm volatile("prefetcht0 %P0" : : "m" (*(const char *)x));
+#endif
+}
+
+void hash_zone(void *zone, unsigned int length)
+{
+	unsigned long temp = htotal;
+
+	while (length >= 8*sizeof(long)) {
+		prefetch(zone + 384);
+		temp ^= *(unsigned long *)zone;
+		temp ^= *(unsigned long *)(zone + sizeof(long));
+		temp ^= *(unsigned long *)(zone + 2*sizeof(long));
+		temp ^= *(unsigned long *)(zone + 3*sizeof(long));
+		temp ^= *(unsigned long *)(zone + 4*sizeof(long));
+		temp ^= *(unsigned long *)(zone + 5*sizeof(long));
+		temp ^= *(unsigned long *)(zone + 6*sizeof(long));
+		temp ^= *(unsigned long *)(zone + 7*sizeof(long));
+		zone += 8*sizeof(long);
+		length -= 8*sizeof(long);
+	}
+	while (length >= 1) {
+		temp ^= *(unsigned char *)zone;
+		zone += 1;
+		length--;
+	}
+	htotal = temp;
+}
+
+void *child_thread(void *arg)
+{
+	unsigned long total_mmap = 0, total = 0;
+	unsigned long delta_usec;
+	int flags = MAP_SHARED;
+	struct timeval t0, t1;
+	char *buffer = NULL;
+	void *oaddr = NULL;
+	double throughput;
+	struct rusage ru;
+	int lu, fd;
+
+	fd = (int)(unsigned long)arg;
+
+	gettimeofday(&t0, NULL);
+
+	fcntl(fd, F_SETFL, O_NDELAY);
+	buffer = malloc(chunk_size);
+	if (!buffer) {
+		perror("malloc");
+		goto error;
+	}
+	while (1) {
+		struct pollfd pfd = { .fd = fd, .events = POLLIN, };
+		int sub;
+
+		poll(&pfd, 1, 10000);
+		if (zflg) {
+			void *naddr;
+
+			naddr = mmap(oaddr, chunk_size, PROT_READ, flags, fd, 0);
+			if (naddr == (void *)-1) {
+				if (errno == EAGAIN) {
+					/* That is if SO_RCVLOWAT is buggy */
+					usleep(1000);
+					continue;
+				}
+				if (errno == EINVAL) {
+					flags = MAP_SHARED;
+					oaddr = NULL;
+					goto fallback;
+				}
+				if (errno != EIO)
+					perror("mmap()");
+				break;
+			}
+			total_mmap += chunk_size;
+			if (xflg)
+				hash_zone(naddr, chunk_size);
+			total += chunk_size;
+			if (!keepflag) {
+				flags |= MAP_FIXED;
+				oaddr = naddr;
+			}
+			continue;
+		}
+fallback:
+		sub = 0;
+		while (sub < chunk_size) {
+			lu = read(fd, buffer + sub, chunk_size - sub);
+			if (lu == 0)
+				goto end;
+			if (lu < 0)
+				break;
+			if (xflg)
+				hash_zone(buffer + sub, lu);
+			total += lu;
+			sub += lu;
+		}
+	}
+end:
+	gettimeofday(&t1, NULL);
+	delta_usec = (t1.tv_sec - t0.tv_sec) * 1000000 + t1.tv_usec - t0.tv_usec;
+
+	throughput = 0;
+	if (delta_usec)
+		throughput = total * 8.0 / (double)delta_usec / 1000.0;
+	getrusage(RUSAGE_THREAD, &ru);
+	if (total > 1024*1024) {
+		unsigned long total_usec;
+		unsigned long mb = total >> 20;
+		total_usec = 1000000*ru.ru_utime.tv_sec + ru.ru_utime.tv_usec +
+			     1000000*ru.ru_stime.tv_sec + ru.ru_stime.tv_usec;
+		printf("received %lg MB (%lg %% mmap'ed) in %lg s, %lg Gbit\n"
+		       "  cpu usage user:%lg sys:%lg, %lg usec per MB, %lu c-switches\n",
+				total / (1024.0 * 1024.0),
+				100.0*total_mmap/total,
+				(double)delta_usec / 1000000.0,
+				throughput,
+				(double)ru.ru_utime.tv_sec + (double)ru.ru_utime.tv_usec / 1000000.0,
+				(double)ru.ru_stime.tv_sec + (double)ru.ru_stime.tv_usec / 1000000.0,
+				(double)total_usec/mb,
+				ru.ru_nvcsw);
+	}
+error:
+	free(buffer);
+	close(fd);
+	pthread_exit(0);
+}
+
+static void apply_rcvsnd_buf(int fd)
+{
+	if (rcvbuf && setsockopt(fd, SOL_SOCKET,
+				 SO_RCVBUF, &rcvbuf, sizeof(rcvbuf)) == -1) {
+		perror("setsockopt SO_RCVBUF");
+	}
+
+	if (sndbuf && setsockopt(fd, SOL_SOCKET,
+				 SO_SNDBUF, &sndbuf, sizeof(sndbuf)) == -1) {
+		perror("setsockopt SO_SNDBUF");
+	}
+}
+
+
+static void setup_sockaddr(int domain, const char *str_addr,
+			   struct sockaddr_storage *sockaddr)
+{
+	struct sockaddr_in6 *addr6 = (void *) sockaddr;
+	struct sockaddr_in *addr4 = (void *) sockaddr;
+
+	switch (domain) {
+	case PF_INET:
+		memset(addr4, 0, sizeof(*addr4));
+		addr4->sin_family = AF_INET;
+		addr4->sin_port = htons(cfg_port);
+		if (str_addr &&
+		    inet_pton(AF_INET, str_addr, &(addr4->sin_addr)) != 1)
+			error(1, 0, "ipv4 parse error: %s", str_addr);
+		break;
+	case PF_INET6:
+		memset(addr6, 0, sizeof(*addr6));
+		addr6->sin6_family = AF_INET6;
+		addr6->sin6_port = htons(cfg_port);
+		if (str_addr &&
+		    inet_pton(AF_INET6, str_addr, &(addr6->sin6_addr)) != 1)
+			error(1, 0, "ipv6 parse error: %s", str_addr);
+		break;
+	default:
+		error(1, 0, "illegal domain");
+	}
+}
+
+static void do_accept(int fdlisten)
+{
+	if (setsockopt(fdlisten, SOL_SOCKET, SO_RCVLOWAT,
+		       &chunk_size, sizeof(chunk_size)) == -1) {
+		perror("setsockopt SO_RCVLOWAT");
+	}
+
+	apply_rcvsnd_buf(fdlisten);
+
+	while (1) {
+		struct sockaddr_in addr;
+		socklen_t addrlen = sizeof(addr);
+		pthread_t th;
+		int fd, res;
+
+		fd = accept(fdlisten, (struct sockaddr *)&addr, &addrlen);
+		if (fd == -1) {
+			perror("accept");
+			continue;
+		}
+		res = pthread_create(&th, NULL, child_thread,
+				     (void *)(unsigned long)fd);
+		if (res) {
+			errno = res;
+			perror("pthread_create");
+			close(fd);
+		}
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	struct sockaddr_storage listenaddr, addr;
+	unsigned int max_pacing_rate = 0;
+	unsigned long total = 0;
+	char *host = NULL;
+	int fd, c, on = 1;
+	char *buffer;
+	int sflg = 0;
+	int mss = 0;
+
+	while ((c = getopt(argc, argv, "46p:svr:w:H:zxkP:M:")) != -1) {
+		switch (c) {
+		case '4':
+			cfg_family = PF_INET;
+			cfg_alen = sizeof(struct sockaddr_in);
+			break;
+		case '6':
+			cfg_family = PF_INET6;
+			cfg_alen = sizeof(struct sockaddr_in6);
+			break;
+		case 'p':
+			cfg_port = atoi(optarg);
+			break;
+		case 'H':
+			host = optarg;
+			break;
+		case 's': /* server : listen for incoming connections */
+			sflg++;
+			break;
+		case 'r':
+			rcvbuf = atoi(optarg);
+			break;
+		case 'w':
+			sndbuf = atoi(optarg);
+			break;
+		case 'z':
+			zflg = 1;
+			break;
+		case 'M':
+			mss = atoi(optarg);
+			break;
+		case 'x':
+			xflg = 1;
+			break;
+		case 'k':
+			keepflag = 1;
+			break;
+		case 'P':
+			max_pacing_rate = atoi(optarg) ;
+			break;
+		default:
+			exit(1);
+		}
+	}
+	if (sflg) {
+		int fdlisten = socket(cfg_family, SOCK_STREAM, 0);
+
+		if (fdlisten == -1) {
+			perror("socket");
+			exit(1);
+		}
+		apply_rcvsnd_buf(fdlisten);
+		setsockopt(fdlisten, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
+
+		setup_sockaddr(cfg_family, host, &listenaddr);
+
+		if (mss &&
+		    setsockopt(fdlisten, SOL_TCP, TCP_MAXSEG, &mss, sizeof(mss)) == -1) {
+			perror("setsockopt TCP_MAXSEG");
+			exit(1);
+		}
+		if (bind(fdlisten, (const struct sockaddr *)&listenaddr, cfg_alen) == -1) {
+			perror("bind");
+			exit(1);
+		}
+		if (listen(fdlisten, 128) == -1) {
+			perror("listen");
+			exit(1);
+		}
+		do_accept(fdlisten);
+	}
+	buffer = mmap(NULL, chunk_size, PROT_READ | PROT_WRITE,
+			      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (buffer == (char *)-1) {
+		perror("mmap");
+		exit(1);
+	}
+
+	fd = socket(AF_INET6, SOCK_STREAM, 0);
+	if (fd == -1) {
+		perror("socket");
+		exit(1);
+	}
+	apply_rcvsnd_buf(fd);
+
+	setup_sockaddr(cfg_family, host, &addr);
+
+	if (mss &&
+	    setsockopt(fd, SOL_TCP, TCP_MAXSEG, &mss, sizeof(mss)) == -1) {
+		perror("setsockopt TCP_MAXSEG");
+		exit(1);
+	}
+	if (connect(fd, (const struct sockaddr *)&addr, cfg_alen) == -1) {
+		perror("connect");
+		exit(1);
+	}
+	if (max_pacing_rate &&
+	    setsockopt(fd, SOL_SOCKET, SO_MAX_PACING_RATE,
+		       &max_pacing_rate, sizeof(max_pacing_rate)) == -1)
+		perror("setsockopt SO_MAX_PACING_RATE");
+
+	if (zflg && setsockopt(fd, SOL_SOCKET, SO_ZEROCOPY,
+			       &on, sizeof(on)) == -1) {
+		perror("setsockopt SO_ZEROCOPY, (-z option disabled)");
+		zflg = 0;
+	}
+	while (total < FILE_SZ) {
+		long wr = FILE_SZ - total;
+
+		if (wr > chunk_size)
+			wr = chunk_size;
+		/* Note : we just want to fill the pipe with 0 bytes */
+		wr = send(fd, buffer, wr, zflg ? MSG_ZEROCOPY : 0);
+		if (wr <= 0)
+			break;
+		total += wr;
+	}
+	close(fd);
+	munmap(buffer, chunk_size);
+	return 0;
+}