[PATCH v3 4/4] vhost-user: add vhost-user

[Laurent Vivier <lvivier@redhat.com>]

add virtio and vhost-user functions to connect with QEMU.

  $ ./passt --vhost-user

and

  # qemu-system-x86_64 ... -m 4G \
        -object memory-backend-memfd,id=memfd0,share=on,size=4G \
        -numa node,memdev=memfd0 \
        -chardev socket,id=chr0,path=/tmp/passt_1.socket \
        -netdev vhost-user,id=netdev0,chardev=chr0 \
        -device virtio-net,mac=9a:2b:2c:2d:2e:2f,netdev=netdev0 \
        ...

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 Makefile       |   6 +-
 checksum.c     |   1 -
 conf.c         |  24 +-
 epoll_type.h   |   4 +
 isolation.c    |  15 +-
 packet.c       |  13 ++
 packet.h       |   2 +
 passt.c        |  25 ++-
 passt.h        |   6 +
 pcap.c         |   1 -
 tap.c          | 106 +++++++--
 tap.h          |   5 +-
 tcp.c          |  33 ++-
 tcp_buf.c      |   6 +-
 tcp_internal.h |   3 +-
 tcp_vu.c       | 593 +++++++++++++++++++++++++++++++++++++++++++++++++
 tcp_vu.h       |  12 +
 udp.c          |  71 +++---
 udp.h          |   8 +-
 udp_internal.h |  34 +++
 udp_vu.c       | 338 ++++++++++++++++++++++++++++
 udp_vu.h       |  13 ++
 vhost_user.c   |  28 ++-
 virtio.c       |   1 -
 vu_common.c    |  27 +++
 vu_common.h    |  34 +++
 26 files changed, 1310 insertions(+), 99 deletions(-)
 create mode 100644 tcp_vu.c
 create mode 100644 tcp_vu.h
 create mode 100644 udp_internal.h
 create mode 100644 udp_vu.c
 create mode 100644 udp_vu.h
 create mode 100644 vu_common.c
 create mode 100644 vu_common.h

diff --git a/Makefile b/Makefile
index 4ccefffacfde..4fb178932f8e 100644
--- a/Makefile
+++ b/Makefile
@@ -47,7 +47,8 @@ FLAGS += -DDUAL_STACK_SOCKETS=$(DUAL_STACK_SOCKETS)
 PASST_SRCS = arch.c arp.c checksum.c conf.c dhcp.c dhcpv6.c flow.c fwd.c \
 	icmp.c igmp.c inany.c iov.c ip.c isolation.c lineread.c log.c mld.c \
 	ndp.c netlink.c packet.c passt.c pasta.c pcap.c pif.c tap.c tcp.c \
-	tcp_buf.c tcp_splice.c udp.c udp_flow.c util.c vhost_user.c virtio.c
+	tcp_buf.c tcp_splice.c tcp_vu.c udp.c udp_flow.c udp_vu.c util.c \
+	vhost_user.c virtio.c vu_common.c
 QRAP_SRCS = qrap.c
 SRCS = $(PASST_SRCS) $(QRAP_SRCS)
 
@@ -57,7 +58,8 @@ PASST_HEADERS = arch.h arp.h checksum.h conf.h dhcp.h dhcpv6.h flow.h fwd.h \
 	flow_table.h icmp.h icmp_flow.h inany.h iov.h ip.h isolation.h \
 	lineread.h log.h ndp.h netlink.h packet.h passt.h pasta.h pcap.h pif.h \
 	siphash.h tap.h tcp.h tcp_buf.h tcp_conn.h tcp_internal.h tcp_splice.h \
-	udp.h udp_flow.h util.h vhost_user.h virtio.h
+	tcp_vu.h udp.h udp_flow.h udp_internal.h udp_vu.h util.h vhost_user.h \
+	virtio.h vu_common.h
 HEADERS = $(PASST_HEADERS) seccomp.h
 
 C := \#include <linux/tcp.h>\nstruct tcp_info x = { .tcpi_snd_wnd = 0 };
diff --git a/checksum.c b/checksum.c
index 006614fcbb28..aa5b7ae1cb66 100644
--- a/checksum.c
+++ b/checksum.c
@@ -501,7 +501,6 @@ uint16_t csum(const void *buf, size_t len, uint32_t init)
  *
  * Return: 16-bit folded, complemented checksum
  */
-/* cppcheck-suppress unusedFunction */
 uint16_t csum_iov(const struct iovec *iov, size_t n, uint32_t init)
 {
 	unsigned int i;
diff --git a/conf.c b/conf.c
index 46fcd9126b4c..c684dbaac694 100644
--- a/conf.c
+++ b/conf.c
@@ -45,6 +45,7 @@
 #include "lineread.h"
 #include "isolation.h"
 #include "log.h"
+#include "vhost_user.h"
 
 /**
  * next_chunk - Return the next piece of a string delimited by a character
@@ -759,9 +760,14 @@ static void usage(const char *name, FILE *f, int status)
 			"    default: same interface name as external one\n");
 	} else {
 		fprintf(f,
-			"  -s, --socket PATH	UNIX domain socket path\n"
+			"  -s, --socket, --socket-path PATH	UNIX domain socket path\n"
 			"    default: probe free path starting from "
 			UNIX_SOCK_PATH "\n", 1);
+		fprintf(f,
+			"  --vhost-user		Enable vhost-user mode\n"
+			"    UNIX domain socket is provided by -s option\n"
+			"  --print-capabilities	print back-end capabilities in JSON format,\n"
+			"    only meaningful for vhost-user mode\n");
 	}
 
 	fprintf(f,
@@ -1230,6 +1236,10 @@ void conf(struct ctx *c, int argc, char **argv)
 		{"no-copy-routes", no_argument,		NULL,		18 },
 		{"no-copy-addrs", no_argument,		NULL,		19 },
 		{"netns-only",	no_argument,		NULL,		20 },
+		{"vhost-user",	no_argument,		NULL,		21 },
+		/* vhost-user backend program convention */
+		{"print-capabilities", no_argument,	NULL,		22 },
+		{"socket-path",	required_argument,	NULL,		's' },
 		{ 0 },
 	};
 	const char *logname = (c->mode == MODE_PASTA) ? "pasta" : "passt";
@@ -1359,14 +1369,12 @@ void conf(struct ctx *c, int argc, char **argv)
 				       sizeof(c->ip4.ifname_out), "%s", optarg);
 			if (ret <= 0 || ret >= (int)sizeof(c->ip4.ifname_out))
 				die("Invalid interface name: %s", optarg);
-
 			break;
 		case 16:
 			ret = snprintf(c->ip6.ifname_out,
 				       sizeof(c->ip6.ifname_out), "%s", optarg);
 			if (ret <= 0 || ret >= (int)sizeof(c->ip6.ifname_out))
 				die("Invalid interface name: %s", optarg);
-
 			break;
 		case 17:
 			if (c->mode != MODE_PASTA)
@@ -1395,6 +1403,16 @@ void conf(struct ctx *c, int argc, char **argv)
 			netns_only = 1;
 			*userns = 0;
 			break;
+		case 21:
+			if (c->mode == MODE_PASTA) {
+				err("--vhost-user is for passt mode only");
+				usage(argv[0], stdout, EXIT_SUCCESS);
+			}
+			c->mode = MODE_VU;
+			break;
+		case 22:
+			vu_print_capabilities();
+			break;
 		case 'd':
 			c->debug = 1;
 			c->quiet = 0;
diff --git a/epoll_type.h b/epoll_type.h
index 0ad1efa0ccec..f3ef41584757 100644
--- a/epoll_type.h
+++ b/epoll_type.h
@@ -36,6 +36,10 @@ enum epoll_type {
 	EPOLL_TYPE_TAP_PASST,
 	/* socket listening for qemu socket connections */
 	EPOLL_TYPE_TAP_LISTEN,
+	/* vhost-user command socket */
+	EPOLL_TYPE_VHOST_CMD,
+	/* vhost-user kick event socket */
+	EPOLL_TYPE_VHOST_KICK,
 
 	EPOLL_NUM_TYPES,
 };
diff --git a/isolation.c b/isolation.c
index 4956d7e6f331..1a27f066c2ba 100644
--- a/isolation.c
+++ b/isolation.c
@@ -373,12 +373,19 @@ void isolate_postfork(const struct ctx *c)
 
 	prctl(PR_SET_DUMPABLE, 0);
 
-	if (c->mode == MODE_PASTA) {
-		prog.len = (unsigned short)ARRAY_SIZE(filter_pasta);
-		prog.filter = filter_pasta;
-	} else {
+	switch (c->mode) {
+	case MODE_PASST:
 		prog.len = (unsigned short)ARRAY_SIZE(filter_passt);
 		prog.filter = filter_passt;
+		break;
+	case MODE_PASTA:
+		prog.len = (unsigned short)ARRAY_SIZE(filter_pasta);
+		prog.filter = filter_pasta;
+		break;
+	case MODE_VU:
+		prog.len = (unsigned short)ARRAY_SIZE(filter_vu);
+		prog.filter = filter_vu;
+		break;
 	}
 
 	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) ||
diff --git a/packet.c b/packet.c
index 37489961a37e..36c7e5070831 100644
--- a/packet.c
+++ b/packet.c
@@ -36,6 +36,19 @@
 static int packet_check_range(const struct pool *p, size_t offset, size_t len,
 			      const char *start, const char *func, int line)
 {
+	ASSERT(p->buf);
+
+	if (p->buf_size == 0) {
+		int ret;
+
+		ret = vu_packet_check_range((void *)p->buf, offset, len, start);
+
+		if (ret == -1)
+			trace("cannot find region, %s:%i", func, line);
+
+		return ret;
+	}
+
 	if (start < p->buf) {
 		trace("packet start %p before buffer start %p, "
 		      "%s:%i", (void *)start, (void *)p->buf, func, line);
diff --git a/packet.h b/packet.h
index 8377dcf678bb..d32688d8a0a4 100644
--- a/packet.h
+++ b/packet.h
@@ -22,6 +22,8 @@ struct pool {
 	struct iovec pkt[1];
 };
 
+int vu_packet_check_range(void *buf, size_t offset, size_t len,
+			  const char *start);
 void packet_add_do(struct pool *p, size_t len, const char *start,
 		   const char *func, int line);
 void *packet_get_do(const struct pool *p, const size_t idx,
diff --git a/passt.c b/passt.c
index 6401730dae65..a931a55ab31b 100644
--- a/passt.c
+++ b/passt.c
@@ -74,6 +74,8 @@ char *epoll_type_str[] = {
 	[EPOLL_TYPE_TAP_PASTA]		= "/dev/net/tun device",
 	[EPOLL_TYPE_TAP_PASST]		= "connected qemu socket",
 	[EPOLL_TYPE_TAP_LISTEN]		= "listening qemu socket",
+	[EPOLL_TYPE_VHOST_CMD]		= "vhost-user command socket",
+	[EPOLL_TYPE_VHOST_KICK]		= "vhost-user kick socket",
 };
 static_assert(ARRAY_SIZE(epoll_type_str) == EPOLL_NUM_TYPES,
 	      "epoll_type_str[] doesn't match enum epoll_type");
@@ -206,6 +208,7 @@ int main(int argc, char **argv)
 	struct rlimit limit;
 	struct timespec now;
 	struct sigaction sa;
+	struct vu_dev vdev;
 
 	clock_gettime(CLOCK_MONOTONIC, &log_start);
 
@@ -262,6 +265,8 @@ int main(int argc, char **argv)
 	pasta_netns_quit_init(&c);
 
 	tap_sock_init(&c);
+	if (c.mode == MODE_VU)
+		vu_init(&c, &vdev);
 
 	secret_init(&c);
 
@@ -350,14 +355,30 @@ loop:
 			tcp_timer_handler(&c, ref);
 			break;
 		case EPOLL_TYPE_UDP_LISTEN:
-			udp_listen_sock_handler(&c, ref, eventmask, &now);
+			if (c.mode == MODE_VU)
+				udp_vu_listen_sock_handler(&c, ref, eventmask,
+							   &now);
+			else
+				udp_buf_listen_sock_handler(&c, ref, eventmask,
+							    &now);
 			break;
 		case EPOLL_TYPE_UDP_REPLY:
-			udp_reply_sock_handler(&c, ref, eventmask, &now);
+			if (c.mode == MODE_VU)
+				udp_vu_reply_sock_handler(&c, ref, eventmask,
+							  &now);
+			else
+				udp_buf_reply_sock_handler(&c, ref, eventmask,
+							   &now);
 			break;
 		case EPOLL_TYPE_PING:
 			icmp_sock_handler(&c, ref);
 			break;
+		case EPOLL_TYPE_VHOST_CMD:
+			tap_handler_vu(&vdev, c.fd_tap, eventmask);
+			break;
+		case EPOLL_TYPE_VHOST_KICK:
+			vu_kick_cb(&vdev, ref, &now);
+			break;
 		default:
 			/* Can't happen */
 			ASSERT(0);
diff --git a/passt.h b/passt.h
index d0f31a230976..71ad32aa3dd0 100644
--- a/passt.h
+++ b/passt.h
@@ -25,6 +25,8 @@ union epoll_ref;
 #include "fwd.h"
 #include "tcp.h"
 #include "udp.h"
+#include "udp_vu.h"
+#include "vhost_user.h"
 
 /**
  * union epoll_ref - Breakdown of reference for epoll fd bookkeeping
@@ -87,6 +89,7 @@ struct fqdn {
 enum passt_modes {
 	MODE_PASST,
 	MODE_PASTA,
+	MODE_VU,
 };
 
 /**
@@ -193,6 +196,7 @@ struct ip6_ctx {
  * @no_map_gw:		Don't map connections, untracked UDP to gateway to host
  * @low_wmem:		Low probed net.core.wmem_max
  * @low_rmem:		Low probed net.core.rmem_max
+ * @vdev:		vhost-user device
  */
 struct ctx {
 	enum passt_modes mode;
@@ -256,6 +260,8 @@ struct ctx {
 
 	int low_wmem;
 	int low_rmem;
+
+	struct vu_dev *vdev;
 };
 
 void proto_update_l2_buf(const unsigned char *eth_d,
diff --git a/pcap.c b/pcap.c
index 46cc4b0d72b6..7e9c56090041 100644
--- a/pcap.c
+++ b/pcap.c
@@ -140,7 +140,6 @@ void pcap_multiple(const struct iovec *iov, size_t frame_parts, unsigned int n,
  *		containing packet data to write, including L2 header
  * @iovcnt:	Number of buffers (@iov entries)
  */
-/* cppcheck-suppress unusedFunction */
 void pcap_iov(const struct iovec *iov, size_t iovcnt)
 {
 	struct timespec now;
diff --git a/tap.c b/tap.c
index 5852705b897c..a25e4e494287 100644
--- a/tap.c
+++ b/tap.c
@@ -58,6 +58,7 @@
 #include "packet.h"
 #include "tap.h"
 #include "log.h"
+#include "vhost_user.h"
 
 /* IPv4 (plus ARP) and IPv6 message batches from tap/guest to IP handlers */
 static PACKET_POOL_NOINIT(pool_tap4, TAP_MSGS, pkt_buf);
@@ -78,16 +79,22 @@ void tap_send_single(const struct ctx *c, const void *data, size_t l2len)
 	struct iovec iov[2];
 	size_t iovcnt = 0;
 
-	if (c->mode == MODE_PASST) {
+	switch (c->mode) {
+	case MODE_PASST:
 		iov[iovcnt] = IOV_OF_LVALUE(vnet_len);
 		iovcnt++;
-	}
-
-	iov[iovcnt].iov_base = (void *)data;
-	iov[iovcnt].iov_len = l2len;
-	iovcnt++;
+		/* fall through */
+	case MODE_PASTA:
+		iov[iovcnt].iov_base = (void *)data;
+		iov[iovcnt].iov_len = l2len;
+		iovcnt++;
 
-	tap_send_frames(c, iov, iovcnt, 1);
+		tap_send_frames(c, iov, iovcnt, 1);
+		break;
+	case MODE_VU:
+		vu_send(c->vdev, data, l2len);
+		break;
+	}
 }
 
 /**
@@ -406,10 +413,18 @@ size_t tap_send_frames(const struct ctx *c, const struct iovec *iov,
 	if (!nframes)
 		return 0;
 
-	if (c->mode == MODE_PASTA)
+	switch (c->mode) {
+	case MODE_PASTA:
 		m = tap_send_frames_pasta(c, iov, bufs_per_frame, nframes);
-	else
+		break;
+	case MODE_PASST:
 		m = tap_send_frames_passt(c, iov, bufs_per_frame, nframes);
+		break;
+	case MODE_VU:
+		/* fall through */
+	default:
+		ASSERT(0);
+	}
 
 	if (m < nframes)
 		debug("tap: failed to send %zu frames of %zu",
@@ -967,7 +982,7 @@ void tap_add_packet(struct ctx *c, ssize_t l2len, char *p)
  * tap_sock_reset() - Handle closing or failure of connect AF_UNIX socket
  * @c:		Execution context
  */
-static void tap_sock_reset(struct ctx *c)
+void tap_sock_reset(struct ctx *c)
 {
 	info("Client connection closed%s", c->one_off ? ", exiting" : "");
 
@@ -978,6 +993,8 @@ static void tap_sock_reset(struct ctx *c)
 	epoll_ctl(c->epollfd, EPOLL_CTL_DEL, c->fd_tap, NULL);
 	close(c->fd_tap);
 	c->fd_tap = -1;
+	if (c->mode == MODE_VU)
+		vu_cleanup(c->vdev);
 }
 
 /**
@@ -1177,11 +1194,17 @@ static void tap_sock_unix_init(struct ctx *c)
 	ev.data.u64 = ref.u64;
 	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap_listen, &ev);
 
-	info("\nYou can now start qemu (>= 7.2, with commit 13c6be96618c):");
-	info("    kvm ... -device virtio-net-pci,netdev=s -netdev stream,id=s,server=off,addr.type=unix,addr.path=%s",
-	     c->sock_path);
-	info("or qrap, for earlier qemu versions:");
-	info("    ./qrap 5 kvm ... -net socket,fd=5 -net nic,model=virtio");
+	if (c->mode == MODE_VU) {
+		info("You can start qemu with:");
+		info("    kvm ... -chardev socket,id=chr0,path=%s -netdev vhost-user,id=netdev0,chardev=chr0 -device virtio-net,netdev=netdev0 -object memory-backend-memfd,id=memfd0,share=on,size=$RAMSIZE -numa node,memdev=memfd0\n",
+		     c->sock_path);
+	} else {
+		info("\nYou can now start qemu (>= 7.2, with commit 13c6be96618c):");
+		info("    kvm ... -device virtio-net-pci,netdev=s -netdev stream,id=s,server=off,addr.type=unix,addr.path=%s",
+		     c->sock_path);
+		info("or qrap, for earlier qemu versions:");
+		info("    ./qrap 5 kvm ... -net socket,fd=5 -net nic,model=virtio");
+	}
 }
 
 /**
@@ -1191,8 +1214,8 @@ static void tap_sock_unix_init(struct ctx *c)
  */
 void tap_listen_handler(struct ctx *c, uint32_t events)
 {
-	union epoll_ref ref = { .type = EPOLL_TYPE_TAP_PASST };
 	struct epoll_event ev = { 0 };
+	union epoll_ref ref;
 	int v = INT_MAX / 2;
 	struct ucred ucred;
 	socklen_t len;
@@ -1232,6 +1255,10 @@ void tap_listen_handler(struct ctx *c, uint32_t events)
 		trace("tap: failed to set SO_SNDBUF to %i", v);
 
 	ref.fd = c->fd_tap;
+	if (c->mode == MODE_VU)
+		ref.type = EPOLL_TYPE_VHOST_CMD;
+	else
+		ref.type = EPOLL_TYPE_TAP_PASST;
 	ev.events = EPOLLIN | EPOLLRDHUP;
 	ev.data.u64 = ref.u64;
 	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
@@ -1293,21 +1320,47 @@ static void tap_sock_tun_init(struct ctx *c)
 	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap, &ev);
 }
 
+void tap_sock_update_buf(void *base, size_t size)
+{
+	int i;
+
+	pool_tap4_storage.buf = base;
+	pool_tap4_storage.buf_size = size;
+	pool_tap6_storage.buf = base;
+	pool_tap6_storage.buf_size = size;
+
+	for (i = 0; i < TAP_SEQS; i++) {
+		tap4_l4[i].p.buf = base;
+		tap4_l4[i].p.buf_size = size;
+		tap6_l4[i].p.buf = base;
+		tap6_l4[i].p.buf_size = size;
+	}
+}
+
 /**
  * tap_sock_init() - Create and set up AF_UNIX socket or tuntap file descriptor
  * @c:		Execution context
  */
 void tap_sock_init(struct ctx *c)
 {
-	size_t sz = sizeof(pkt_buf);
+	size_t sz;
+	char *buf;
 	int i;
 
-	pool_tap4_storage = PACKET_INIT(pool_tap4, TAP_MSGS, pkt_buf, sz);
-	pool_tap6_storage = PACKET_INIT(pool_tap6, TAP_MSGS, pkt_buf, sz);
+	if (c->mode == MODE_VU) {
+		buf = NULL;
+		sz = 0;
+	} else {
+		buf = pkt_buf;
+		sz = sizeof(pkt_buf);
+	}
+
+	pool_tap4_storage = PACKET_INIT(pool_tap4, TAP_MSGS, buf, sz);
+	pool_tap6_storage = PACKET_INIT(pool_tap6, TAP_MSGS, buf, sz);
 
 	for (i = 0; i < TAP_SEQS; i++) {
-		tap4_l4[i].p = PACKET_INIT(pool_l4, UIO_MAXIOV, pkt_buf, sz);
-		tap6_l4[i].p = PACKET_INIT(pool_l4, UIO_MAXIOV, pkt_buf, sz);
+		tap4_l4[i].p = PACKET_INIT(pool_l4, UIO_MAXIOV, buf, sz);
+		tap6_l4[i].p = PACKET_INIT(pool_l4, UIO_MAXIOV, buf, sz);
 	}
 
 	if (c->fd_tap != -1) { /* Passed as --fd */
@@ -1316,10 +1369,17 @@ void tap_sock_init(struct ctx *c)
 
 		ASSERT(c->one_off);
 		ref.fd = c->fd_tap;
-		if (c->mode == MODE_PASST)
+		switch (c->mode) {
+		case MODE_PASST:
 			ref.type = EPOLL_TYPE_TAP_PASST;
-		else
+			break;
+		case MODE_PASTA:
 			ref.type = EPOLL_TYPE_TAP_PASTA;
+			break;
+		case MODE_VU:
+			ref.type = EPOLL_TYPE_VHOST_CMD;
+			break;
+		}
 
 		ev.events = EPOLLIN | EPOLLRDHUP;
 		ev.data.u64 = ref.u64;
diff --git a/tap.h b/tap.h
index ec9e2acec460..c5447f7077eb 100644
--- a/tap.h
+++ b/tap.h
@@ -40,7 +40,8 @@ static inline struct iovec tap_hdr_iov(const struct ctx *c,
  */
 static inline void tap_hdr_update(struct tap_hdr *thdr, size_t l2len)
 {
-	thdr->vnet_len = htonl(l2len);
+	if (thdr)
+		thdr->vnet_len = htonl(l2len);
 }
 
 void tap_udp4_send(const struct ctx *c, struct in_addr src, in_port_t sport,
@@ -68,6 +69,8 @@ void tap_handler_pasta(struct ctx *c, uint32_t events,
 void tap_handler_passt(struct ctx *c, uint32_t events,
 		       const struct timespec *now);
 int tap_sock_unix_open(char *sock_path);
+void tap_sock_reset(struct ctx *c);
+void tap_sock_update_buf(void *base, size_t size);
 void tap_sock_init(struct ctx *c);
 void tap_flush_pools(void);
 void tap_handler(struct ctx *c, const struct timespec *now);
diff --git a/tcp.c b/tcp.c
index c0820ce7a391..1af99b2ae042 100644
--- a/tcp.c
+++ b/tcp.c
@@ -304,6 +304,7 @@
 #include "flow_table.h"
 #include "tcp_internal.h"
 #include "tcp_buf.h"
+#include "tcp_vu.h"
 
 /* MSS rounding: see SET_MSS() */
 #define MSS_DEFAULT			536
@@ -896,6 +897,7 @@ static void tcp_fill_header(struct tcphdr *th,
 
 /**
  * tcp_fill_headers4() - Fill 802.3, IPv4, TCP headers in pre-cooked buffers
+ * @c:		Execution context
  * @conn:	Connection pointer
  * @taph:	tap backend specific header
  * @iph:	Pointer to IPv4 header
@@ -906,7 +908,8 @@ static void tcp_fill_header(struct tcphdr *th,
  *
  * Return: The IPv4 payload length, host order
  */
-static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
+static size_t tcp_fill_headers4(const struct ctx *c,
+				const struct tcp_tap_conn *conn,
 				struct tap_hdr *taph,
 				struct iphdr *iph, struct tcphdr *th,
 				size_t dlen, const uint16_t *check,
@@ -929,7 +932,10 @@ static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
 
 	tcp_fill_header(th, conn, seq);
 
-	tcp_update_check_tcp4(iph, th);
+	if (c->mode != MODE_VU)
+		tcp_update_check_tcp4(iph, th);
+	else
+		th->check = 0;
 
 	tap_hdr_update(taph, l3len + sizeof(struct ethhdr));
 
@@ -938,6 +944,7 @@ static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
 
 /**
  * tcp_fill_headers6() - Fill 802.3, IPv6, TCP headers in pre-cooked buffers
+ * @c:		Execution context
  * @conn:	Connection pointer
  * @taph:	tap backend specific header
  * @ip6h:	Pointer to IPv6 header
@@ -948,7 +955,8 @@ static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
  *
  * Return: The IPv6 payload length, host order
  */
-static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
+static size_t tcp_fill_headers6(const struct ctx *c,
+				const struct tcp_tap_conn *conn,
 				struct tap_hdr *taph,
 				struct ipv6hdr *ip6h, struct tcphdr *th,
 				size_t dlen, uint32_t seq)
@@ -970,7 +978,10 @@ static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
 
 	tcp_fill_header(th, conn, seq);
 
-	tcp_update_check_tcp6(ip6h, th);
+	if (c->mode != MODE_VU)
+		tcp_update_check_tcp6(ip6h, th);
+	else
+		th->check = 0;
 
 	tap_hdr_update(taph, l4len + sizeof(*ip6h) + sizeof(struct ethhdr));
 
@@ -979,6 +990,7 @@ static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
 
 /**
  * tcp_l2_buf_fill_headers() - Fill 802.3, IP, TCP headers in pre-cooked buffers
+ * @c:		Execution context
  * @conn:	Connection pointer
  * @iov:	Pointer to an array of iovec of TCP pre-cooked buffers
  * @dlen:	TCP payload length
@@ -987,7 +999,8 @@ static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
  *
  * Return: IP payload length, host order
  */
-size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
+size_t tcp_l2_buf_fill_headers(const struct ctx *c,
+			       const struct tcp_tap_conn *conn,
 			       struct iovec *iov, size_t dlen,
 			       const uint16_t *check, uint32_t seq)
 {
@@ -995,13 +1008,13 @@ size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
 	const struct in_addr *a4 = inany_v4(&tapside->faddr);
 
 	if (a4) {
-		return tcp_fill_headers4(conn, iov[TCP_IOV_TAP].iov_base,
+		return tcp_fill_headers4(c, conn, iov[TCP_IOV_TAP].iov_base,
 					 iov[TCP_IOV_IP].iov_base,
 					 iov[TCP_IOV_PAYLOAD].iov_base, dlen,
 					 check, seq);
 	}
 
-	return tcp_fill_headers6(conn, iov[TCP_IOV_TAP].iov_base,
+	return tcp_fill_headers6(c, conn, iov[TCP_IOV_TAP].iov_base,
 				 iov[TCP_IOV_IP].iov_base,
 				 iov[TCP_IOV_PAYLOAD].iov_base, dlen,
 				 seq);
@@ -1237,6 +1250,9 @@ int tcp_prepare_flags(struct ctx *c, struct tcp_tap_conn *conn,
  */
 int tcp_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
 {
+	if (c->mode == MODE_VU)
+		return tcp_vu_send_flag(c, conn, flags);
+
 	return tcp_buf_send_flag(c, conn, flags);
 }
 
@@ -1630,6 +1646,9 @@ static int tcp_sock_consume(const struct tcp_tap_conn *conn, uint32_t ack_seq)
  */
 static int tcp_data_from_sock(struct ctx *c, struct tcp_tap_conn *conn)
 {
+	if (c->mode == MODE_VU)
+		return tcp_vu_data_from_sock(c, conn);
+
 	return tcp_buf_data_from_sock(c, conn);
 }
 
diff --git a/tcp_buf.c b/tcp_buf.c
index c31e9f31b438..6b702b00be89 100644
--- a/tcp_buf.c
+++ b/tcp_buf.c
@@ -321,7 +321,7 @@ int tcp_buf_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
 		return ret;
 	}
 
-	l4len = tcp_l2_buf_fill_headers(conn, iov, optlen, NULL, seq);
+	l4len = tcp_l2_buf_fill_headers(c, conn, iov, optlen, NULL, seq);
 	iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 
 	if (flags & DUP_ACK) {
@@ -378,7 +378,7 @@ static void tcp_data_to_tap(struct ctx *c, struct tcp_tap_conn *conn,
 		tcp4_frame_conns[tcp4_payload_used] = conn;
 
 		iov = tcp4_l2_iov[tcp4_payload_used++];
-		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, check, seq);
+		l4len = tcp_l2_buf_fill_headers(c, conn, iov, dlen, check, seq);
 		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 		if (tcp4_payload_used > TCP_FRAMES_MEM - 1)
 			tcp_payload_flush(c);
@@ -386,7 +386,7 @@ static void tcp_data_to_tap(struct ctx *c, struct tcp_tap_conn *conn,
 		tcp6_frame_conns[tcp6_payload_used] = conn;
 
 		iov = tcp6_l2_iov[tcp6_payload_used++];
-		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, NULL, seq);
+		l4len = tcp_l2_buf_fill_headers(c, conn, iov, dlen, NULL, seq);
 		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 		if (tcp6_payload_used > TCP_FRAMES_MEM - 1)
 			tcp_payload_flush(c);
diff --git a/tcp_internal.h b/tcp_internal.h
index 8b60aabc1b33..3dd4b49a4441 100644
--- a/tcp_internal.h
+++ b/tcp_internal.h
@@ -89,7 +89,8 @@ void tcp_rst_do(struct ctx *c, struct tcp_tap_conn *conn);
 		tcp_rst_do(c, conn);					\
 	} while (0)
 
-size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
+size_t tcp_l2_buf_fill_headers(const struct ctx *c,
+			       const struct tcp_tap_conn *conn,
 			       struct iovec *iov, size_t dlen,
 			       const uint16_t *check, uint32_t seq);
 int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn,
diff --git a/tcp_vu.c b/tcp_vu.c
new file mode 100644
index 000000000000..6eef9187dbd7
--- /dev/null
+++ b/tcp_vu.c
@@ -0,0 +1,593 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: Laurent Vivier <lvivier@redhat.com>
+ *
+ * tcp_vu.c - TCP L2 vhost-user management functions
+ */
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include <netinet/ip.h>
+
+#include <sys/socket.h>
+
+#include <linux/tcp.h>
+#include <linux/virtio_net.h>
+
+#include "util.h"
+#include "ip.h"
+#include "passt.h"
+#include "siphash.h"
+#include "inany.h"
+#include "vhost_user.h"
+#include "tcp.h"
+#include "pcap.h"
+#include "flow.h"
+#include "tcp_conn.h"
+#include "flow_table.h"
+#include "tcp_vu.h"
+#include "tcp_internal.h"
+#include "checksum.h"
+#include "vu_common.h"
+
+/**
+ * struct tcp_payload_t - TCP header and data to send segments with payload
+ * @th:		TCP header
+ * @data:	TCP data
+ */
+struct tcp_payload_t {
+	struct tcphdr th;
+	uint8_t data[IP_MAX_MTU - sizeof(struct tcphdr)];
+};
+
+/**
+ * struct tcp_flags_t - TCP header and data to send zero-length
+ *                      segments (flags)
+ * @th:		TCP header
+ * @opts	TCP options
+ */
+struct tcp_flags_t {
+	struct tcphdr th;
+	char opts[OPT_MSS_LEN + OPT_WS_LEN + 1];
+};
+
+/* vhost-user */
+static const struct virtio_net_hdr vu_header = {
+	.flags = VIRTIO_NET_HDR_F_DATA_VALID,
+	.gso_type = VIRTIO_NET_HDR_GSO_NONE,
+};
+
+static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE];
+static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
+
+static size_t tcp_vu_l2_hdrlen(const struct vu_dev *vdev, bool v6)
+{
+	size_t l2_hdrlen;
+
+	l2_hdrlen = vdev->hdrlen + sizeof(struct ethhdr) +
+		    sizeof(struct tcphdr);
+
+	if (v6)
+		l2_hdrlen += sizeof(struct ipv6hdr);
+	else
+		l2_hdrlen += sizeof(struct iphdr);
+
+	return l2_hdrlen;
+}
+
+static void tcp_vu_pcap(const struct ctx *c, const struct flowside *tapside,
+			struct iovec *iov, int iov_used, size_t l4len)
+{
+	const struct in_addr *src = inany_v4(&tapside->faddr);
+	const struct in_addr *dst = inany_v4(&tapside->eaddr);
+	const struct vu_dev *vdev = c->vdev;
+	char *base = iov[0].iov_base;
+	size_t size = iov[0].iov_len;
+	struct tcp_payload_t *bp;
+	uint32_t sum;
+
+	if (!*c->pcap)
+		return;
+
+	if (src && dst) {
+		bp = vu_payloadv4(vdev, base);
+		sum = proto_ipv4_header_psum(l4len, IPPROTO_TCP,
+					     *src, *dst);
+	} else {
+		bp = vu_payloadv6(vdev, base);
+		sum = proto_ipv6_header_psum(l4len, IPPROTO_TCP,
+					     &tapside->faddr.a6,
+					     &tapside->eaddr.a6);
+	}
+	iov[0].iov_base = &bp->th;
+	iov[0].iov_len = size - ((char *)iov[0].iov_base - base);
+	bp->th.check = 0;
+	bp->th.check = csum_iov(iov, iov_used, sum);
+
+	/* set iov for pcap logging */
+	iov[0].iov_base = base + vdev->hdrlen;
+	iov[0].iov_len = size - vdev->hdrlen;
+
+	pcap_iov(iov, iov_used);
+
+	/* restore iov[0] */
+	iov[0].iov_base = base;
+	iov[0].iov_len = size;
+}
+
+int tcp_vu_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
+{
+	struct vu_dev *vdev = c->vdev;
+	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
+	const struct flowside *tapside = TAPFLOW(conn);
+	struct virtio_net_hdr_mrg_rxbuf *vh;
+	struct iovec l2_iov[TCP_NUM_IOVS];
+	size_t l2len, l4len, optlen;
+	struct iovec in_sg;
+	struct ethhdr *eh;
+	int nb_ack;
+	int ret;
+
+	elem[0].out_num = 0;
+	elem[0].out_sg = NULL;
+	elem[0].in_num = 1;
+	elem[0].in_sg = &in_sg;
+	ret = vu_queue_pop(vdev, vq, &elem[0]);
+	if (ret < 0)
+		return 0;
+
+	if (elem[0].in_num < 1) {
+		err("virtio-net receive queue contains no in buffers");
+		vu_queue_rewind(vq, 1);
+		return 0;
+	}
+
+	vh = elem[0].in_sg[0].iov_base;
+
+	vh->hdr = vu_header;
+	if (vdev->hdrlen == sizeof(struct virtio_net_hdr_mrg_rxbuf))
+		vh->num_buffers = htole16(1);
+
+	l2_iov[TCP_IOV_TAP].iov_base = NULL;
+	l2_iov[TCP_IOV_TAP].iov_len = 0;
+	l2_iov[TCP_IOV_ETH].iov_base = (char *)elem[0].in_sg[0].iov_base + vdev->hdrlen;
+	l2_iov[TCP_IOV_ETH].iov_len = sizeof(struct ethhdr);
+
+	eh = l2_iov[TCP_IOV_ETH].iov_base;
+
+	memcpy(eh->h_dest, c->mac_guest, sizeof(eh->h_dest));
+	memcpy(eh->h_source, c->mac, sizeof(eh->h_source));
+
+	if (CONN_V4(conn)) {
+		struct tcp_flags_t *payload;
+		struct iphdr *iph;
+		uint32_t seq;
+
+		l2_iov[TCP_IOV_IP].iov_base = (char *)l2_iov[TCP_IOV_ETH].iov_base +
+						      l2_iov[TCP_IOV_ETH].iov_len;
+		l2_iov[TCP_IOV_IP].iov_len = sizeof(struct iphdr);
+		l2_iov[TCP_IOV_PAYLOAD].iov_base = (char *)l2_iov[TCP_IOV_IP].iov_base +
+							   l2_iov[TCP_IOV_IP].iov_len;
+
+		eh->h_proto = htons(ETH_P_IP);
+
+		iph = l2_iov[TCP_IOV_IP].iov_base;
+		*iph = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_TCP);
+
+		payload = l2_iov[TCP_IOV_PAYLOAD].iov_base;
+		payload->th = (struct tcphdr){
+			.doff = offsetof(struct tcp_flags_t, opts) / 4,
+			.ack = 1
+		};
+
+		seq = conn->seq_to_tap;
+		ret = tcp_prepare_flags(c, conn, flags, &payload->th, payload->opts, &optlen);
+		if (ret <= 0) {
+			vu_queue_rewind(vq, 1);
+			return ret;
+		}
+
+		l4len = tcp_l2_buf_fill_headers(c, conn, l2_iov, optlen, NULL,
+						seq);
+		/* keep the following assignment for clarity */
+		/* cppcheck-suppress unreadVariable */
+		l2_iov[TCP_IOV_PAYLOAD].iov_len = l4len;
+
+		l2len = l4len + sizeof(*iph) + sizeof(struct ethhdr);
+	} else {
+		struct tcp_flags_t *payload;
+		struct ipv6hdr *ip6h;
+		uint32_t seq;
+
+		l2_iov[TCP_IOV_IP].iov_base = (char *)l2_iov[TCP_IOV_ETH].iov_base +
+						      l2_iov[TCP_IOV_ETH].iov_len;
+		l2_iov[TCP_IOV_IP].iov_len = sizeof(struct ipv6hdr);
+		l2_iov[TCP_IOV_PAYLOAD].iov_base = (char *)l2_iov[TCP_IOV_IP].iov_base +
+							   l2_iov[TCP_IOV_IP].iov_len;
+
+		eh->h_proto = htons(ETH_P_IPV6);
+
+		ip6h = l2_iov[TCP_IOV_IP].iov_base;
+		*ip6h = (struct ipv6hdr)L2_BUF_IP6_INIT(IPPROTO_TCP);
+
+		payload = l2_iov[TCP_IOV_PAYLOAD].iov_base;
+		payload->th = (struct tcphdr){
+			.doff = offsetof(struct tcp_flags_t, opts) / 4,
+			.ack = 1
+		};
+
+		seq = conn->seq_to_tap;
+		ret = tcp_prepare_flags(c, conn, flags, &payload->th, payload->opts, &optlen);
+		if (ret <= 0) {
+			vu_queue_rewind(vq, 1);
+			return ret;
+		}
+
+		l4len = tcp_l2_buf_fill_headers(c, conn, l2_iov, optlen, NULL,
+						seq);
+		/* keep the following assignment for clarity */
+		/* cppcheck-suppress unreadVariable */
+		l2_iov[TCP_IOV_PAYLOAD].iov_len = l4len;
+
+		l2len = l4len + sizeof(*ip6h) + sizeof(struct ethhdr);
+	}
+	l2len += vdev->hdrlen;
+	ASSERT(l2len <= elem[0].in_sg[0].iov_len);
+
+	elem[0].in_sg[0].iov_len = l2len;
+	tcp_vu_pcap(c, tapside, &elem[0].in_sg[0], 1, l4len);
+
+	vu_queue_fill(vq, &elem[0], l2len, 0);
+	nb_ack = 1;
+
+	if (flags & DUP_ACK) {
+		struct iovec in_sg_dup;
+
+		elem[1].out_num = 0;
+		elem[1].out_sg = NULL;
+		elem[1].in_num = 1;
+		elem[1].in_sg = &in_sg_dup;
+		ret = vu_queue_pop(vdev, vq, &elem[1]);
+		if (ret == 0) {
+			if (elem[1].in_num < 1 || elem[1].in_sg[0].iov_len < l2len) {
+				vu_queue_rewind(vq, 1);
+			} else {
+				memcpy(elem[1].in_sg[0].iov_base, vh, l2len);
+				nb_ack++;
+
+				tcp_vu_pcap(c, tapside, &elem[1].in_sg[0], 1,
+					    l4len);
+
+				vu_queue_fill(vq, &elem[1], l2len, 1);
+			}
+		}
+	}
+
+	vu_queue_flush(vq, nb_ack);
+	vu_queue_notify(vdev, vq);
+
+	return 0;
+}
+
+static ssize_t tcp_vu_sock_recv(struct ctx *c,
+				struct tcp_tap_conn *conn, bool v4,
+				size_t fillsize, uint16_t mss,
+				ssize_t *data_len)
+{
+	struct vu_dev *vdev = c->vdev;
+	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
+	static struct iovec in_sg[VIRTQUEUE_MAX_SIZE];
+	struct msghdr mh_sock = { 0 };
+	static int in_sg_count;
+	int s = conn->sock;
+	size_t l2_hdrlen;
+	int segment_size;
+	int iov_cnt;
+	ssize_t ret;
+
+	l2_hdrlen = tcp_vu_l2_hdrlen(vdev, !v4);
+
+	iov_cnt = 0;
+	in_sg_count = 0;
+	segment_size = 0;
+	*data_len = 0;
+	while (fillsize > 0 && iov_cnt < VIRTQUEUE_MAX_SIZE - 1 &&
+			       in_sg_count < ARRAY_SIZE(in_sg)) {
+
+		elem[iov_cnt].out_num = 0;
+		elem[iov_cnt].out_sg = NULL;
+		elem[iov_cnt].in_num = ARRAY_SIZE(in_sg) - in_sg_count;
+		elem[iov_cnt].in_sg = &in_sg[in_sg_count];
+		ret = vu_queue_pop(vdev, vq, &elem[iov_cnt]);
+		if (ret < 0)
+			break;
+
+		if (elem[iov_cnt].in_num < 1)
+			die("virtio-net receive queue contains no in buffers");
+
+		in_sg_count += elem[iov_cnt].in_num;
+
+		ASSERT(elem[iov_cnt].in_num == 1);
+		ASSERT(elem[iov_cnt].in_sg[0].iov_len >= l2_hdrlen);
+
+		if (segment_size == 0) {
+			iov_vu[iov_cnt + 1].iov_base =
+					(char *)elem[iov_cnt].in_sg[0].iov_base + l2_hdrlen;
+			iov_vu[iov_cnt + 1].iov_len =
+					elem[iov_cnt].in_sg[0].iov_len - l2_hdrlen;
+		} else {
+			iov_vu[iov_cnt + 1].iov_base = elem[iov_cnt].in_sg[0].iov_base;
+			iov_vu[iov_cnt + 1].iov_len = elem[iov_cnt].in_sg[0].iov_len;
+		}
+
+		if (iov_vu[iov_cnt + 1].iov_len > fillsize)
+			iov_vu[iov_cnt + 1].iov_len = fillsize;
+
+		segment_size += iov_vu[iov_cnt + 1].iov_len;
+		if (vdev->hdrlen != sizeof(struct virtio_net_hdr_mrg_rxbuf)) {
+			segment_size = 0;
+		} else if (segment_size >= mss) {
+			iov_vu[iov_cnt + 1].iov_len -= segment_size - mss;
+			segment_size = 0;
+		}
+		fillsize -= iov_vu[iov_cnt + 1].iov_len;
+
+		iov_cnt++;
+	}
+	if (iov_cnt == 0)
+		return 0;
+
+	mh_sock.msg_iov = iov_vu;
+	mh_sock.msg_iovlen = iov_cnt + 1;
+
+	do
+		ret = recvmsg(s, &mh_sock, MSG_PEEK);
+	while (ret < 0 && errno == EINTR);
+
+	if (ret < 0) {
+		vu_queue_rewind(vq, iov_cnt);
+		if (errno != EAGAIN && errno != EWOULDBLOCK) {
+			ret = -errno;
+			tcp_rst(c, conn);
+		}
+		return ret;
+	}
+	if (!ret) {
+		vu_queue_rewind(vq, iov_cnt);
+
+		if ((conn->events & (SOCK_FIN_RCVD | TAP_FIN_SENT)) == SOCK_FIN_RCVD) {
+			int retf = tcp_vu_send_flag(c, conn, FIN | ACK);
+			if (retf) {
+				tcp_rst(c, conn);
+				return retf;
+			}
+
+			conn_event(c, conn, TAP_FIN_SENT);
+		}
+		return 0;
+	}
+
+	*data_len = ret;
+	return iov_cnt;
+}
+
+static size_t tcp_vu_prepare(const struct ctx *c,
+			     struct tcp_tap_conn *conn, struct iovec *first,
+			     size_t data_len, const uint16_t **check)
+{
+	const struct flowside *toside = TAPFLOW(conn);
+	const struct vu_dev *vdev = c->vdev;
+	struct iovec l2_iov[TCP_NUM_IOVS];
+	char *base = first->iov_base;
+	struct ethhdr *eh;
+	size_t l4len;
+
+	/* we guess the first iovec provided by the guest can embed
+         * all the headers needed by L2 frame
+         */
+
+	l2_iov[TCP_IOV_TAP].iov_base = NULL;
+	l2_iov[TCP_IOV_TAP].iov_len = 0;
+	l2_iov[TCP_IOV_ETH].iov_base = base + vdev->hdrlen;
+	l2_iov[TCP_IOV_ETH].iov_len = sizeof(struct ethhdr);
+
+	eh = l2_iov[TCP_IOV_ETH].iov_base;
+
+	memcpy(eh->h_dest, c->mac_guest, sizeof(eh->h_dest));
+	memcpy(eh->h_source, c->mac, sizeof(eh->h_source));
+
+	/* initialize header */
+	if (inany_v4(&toside->eaddr) && inany_v4(&toside->faddr)) {
+		struct tcp_payload_t *payload;
+		struct iphdr *iph;
+
+		ASSERT(first[0].iov_len >= vdev->hdrlen +
+		       sizeof(struct ethhdr) + sizeof(struct iphdr) +
+		       sizeof(struct tcphdr));
+
+		l2_iov[TCP_IOV_IP].iov_base = (char *)l2_iov[TCP_IOV_ETH].iov_base +
+						      l2_iov[TCP_IOV_ETH].iov_len;
+		l2_iov[TCP_IOV_IP].iov_len = sizeof(struct iphdr);
+		l2_iov[TCP_IOV_PAYLOAD].iov_base = (char *)l2_iov[TCP_IOV_IP].iov_base +
+							   l2_iov[TCP_IOV_IP].iov_len;
+
+
+		eh->h_proto = htons(ETH_P_IP);
+
+		iph = l2_iov[TCP_IOV_IP].iov_base;
+		*iph = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_TCP);
+		payload = l2_iov[TCP_IOV_PAYLOAD].iov_base;
+		payload->th = (struct tcphdr){
+			.doff = offsetof(struct tcp_payload_t, data) / 4,
+			.ack = 1
+		};
+
+		l4len = tcp_l2_buf_fill_headers(c, conn, l2_iov,
+						data_len, *check,
+						conn->seq_to_tap);
+		/* keep the following assignment for clarity */
+		/* cppcheck-suppress unreadVariable */
+		l2_iov[TCP_IOV_PAYLOAD].iov_len = l4len;
+
+		*check = &iph->check;
+	} else {
+		struct tcp_payload_t *payload;
+		struct ipv6hdr *ip6h;
+
+		ASSERT(first[0].iov_len >= vdev->hdrlen +
+		       sizeof(struct ethhdr) + sizeof(struct ipv6hdr) +
+		       sizeof(struct tcphdr));
+
+		l2_iov[TCP_IOV_IP].iov_base = (char *)l2_iov[TCP_IOV_ETH].iov_base +
+						      l2_iov[TCP_IOV_ETH].iov_len;
+		l2_iov[TCP_IOV_IP].iov_len = sizeof(struct ipv6hdr);
+		l2_iov[TCP_IOV_PAYLOAD].iov_base = (char *)l2_iov[TCP_IOV_IP].iov_base +
+							   l2_iov[TCP_IOV_IP].iov_len;
+
+
+		eh->h_proto = htons(ETH_P_IPV6);
+
+		ip6h = l2_iov[TCP_IOV_IP].iov_base;
+		*ip6h = (struct ipv6hdr)L2_BUF_IP6_INIT(IPPROTO_TCP);
+
+		payload = l2_iov[TCP_IOV_PAYLOAD].iov_base;
+		payload->th = (struct tcphdr){
+			.doff = offsetof(struct tcp_payload_t, data) / 4,
+			.ack = 1
+		};
+;
+		l4len = tcp_l2_buf_fill_headers(c, conn, l2_iov,
+						data_len,
+						NULL, conn->seq_to_tap);
+		/* keep the following assignment for clarity */
+		/* cppcheck-suppress unreadVariable */
+		l2_iov[TCP_IOV_PAYLOAD].iov_len = l4len;
+	}
+
+	return l4len;
+}
+
+int tcp_vu_data_from_sock(struct ctx *c, struct tcp_tap_conn *conn)
+{
+	uint32_t wnd_scaled = conn->wnd_from_tap << conn->ws_from_tap;
+	struct vu_dev *vdev = c->vdev;
+	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
+	const struct flowside *tapside = TAPFLOW(conn);
+	uint16_t mss = MSS_GET(conn);
+	size_t l2_hdrlen, fillsize;
+	int i, iov_cnt, iov_used;
+	int v4 = CONN_V4(conn);
+	uint32_t already_sent;
+	const uint16_t *check;
+	struct iovec *first;
+	int segment_size;
+	int num_buffers;
+	ssize_t len;
+
+	if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) {
+		flow_err(conn,
+			 "Got packet, but no available descriptors on RX virtq.");
+		return 0;
+	}
+
+	already_sent = conn->seq_to_tap - conn->seq_ack_from_tap;
+
+	if (SEQ_LT(already_sent, 0)) {
+		/* RFC 761, section 2.1. */
+		flow_trace(conn, "ACK sequence gap: ACK for %u, sent: %u",
+			   conn->seq_ack_from_tap, conn->seq_to_tap);
+		conn->seq_to_tap = conn->seq_ack_from_tap;
+		already_sent = 0;
+	}
+
+	if (!wnd_scaled || already_sent >= wnd_scaled) {
+		conn_flag(c, conn, STALLED);
+		conn_flag(c, conn, ACK_FROM_TAP_DUE);
+		return 0;
+	}
+
+	/* Set up buffer descriptors we'll fill completely and partially. */
+
+	fillsize = wnd_scaled;
+
+	iov_vu[0].iov_base = tcp_buf_discard;
+	iov_vu[0].iov_len = already_sent;
+	fillsize -= already_sent;
+
+	iov_cnt = tcp_vu_sock_recv(c, conn, v4, fillsize, mss, &len);
+	if (iov_cnt <= 0)
+		return iov_cnt;
+
+	len -= already_sent;
+	if (len <= 0) {
+		conn_flag(c, conn, STALLED);
+		vu_queue_rewind(vq, iov_cnt);
+		return 0;
+	}
+
+	conn_flag(c, conn, ~STALLED);
+
+	/* Likely, some new data was acked too. */
+	tcp_update_seqack_wnd(c, conn, 0, NULL);
+
+	/* initialize headers */
+	l2_hdrlen = tcp_vu_l2_hdrlen(vdev, !v4);
+	iov_used = 0;
+	num_buffers = 0;
+	check = NULL;
+	segment_size = 0;
+	for (i = 0; i < iov_cnt && len; i++) {
+
+		if (segment_size == 0)
+			first = &iov_vu[i + 1];
+
+		if (iov_vu[i + 1].iov_len > (size_t)len)
+			iov_vu[i + 1].iov_len = len;
+
+		len -= iov_vu[i + 1].iov_len;
+		iov_used++;
+
+		segment_size += iov_vu[i + 1].iov_len;
+		num_buffers++;
+
+		if (segment_size >= mss || len == 0 ||
+		    i + 1 == iov_cnt || vdev->hdrlen != sizeof(struct virtio_net_hdr_mrg_rxbuf)) {
+			struct virtio_net_hdr_mrg_rxbuf *vh;
+			size_t l4len;
+
+			if (i + 1 == iov_cnt)
+				check = NULL;
+
+			/* restore first iovec base: point to vnet header */
+			first->iov_base = (char *)first->iov_base - l2_hdrlen;
+			first->iov_len = first->iov_len + l2_hdrlen;
+
+			vh = first->iov_base;
+
+			vh->hdr = vu_header;
+			if (vdev->hdrlen == sizeof(struct virtio_net_hdr_mrg_rxbuf))
+				vh->num_buffers = htole16(num_buffers);
+
+			l4len = tcp_vu_prepare(c, conn, first, segment_size, &check);
+
+			tcp_vu_pcap(c, tapside, first, num_buffers, l4len);
+
+			conn->seq_to_tap += segment_size;
+
+			segment_size = 0;
+			num_buffers = 0;
+		}
+	}
+
+	/* release unused buffers */
+	vu_queue_rewind(vq, iov_cnt - iov_used);
+
+	/* send packets */
+	vu_send_frame(vdev, vq, elem, &iov_vu[1], iov_used);
+
+	conn_flag(c, conn, ACK_FROM_TAP_DUE);
+
+	return 0;
+}
diff --git a/tcp_vu.h b/tcp_vu.h
new file mode 100644
index 000000000000..99daba5b34ed
--- /dev/null
+++ b/tcp_vu.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: Laurent Vivier <lvivier@redhat.com>
+ */
+
+#ifndef TCP_VU_H
+#define TCP_VU_H
+
+int tcp_vu_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags);
+int tcp_vu_data_from_sock(struct ctx *c, struct tcp_tap_conn *conn);
+
+#endif  /*TCP_VU_H */
diff --git a/udp.c b/udp.c
index 7731257292e1..4d2afc62478a 100644
--- a/udp.c
+++ b/udp.c
@@ -109,8 +109,7 @@
 #include "pcap.h"
 #include "log.h"
 #include "flow_table.h"
-
-#define UDP_MAX_FRAMES		32  /* max # of frames to receive at once */
+#include "udp_internal.h"
 
 /* "Spliced" sockets indexed by bound port (host order) */
 static int udp_splice_ns  [IP_VERSIONS][NUM_PORTS];
@@ -118,20 +117,8 @@ static int udp_splice_init[IP_VERSIONS][NUM_PORTS];
 
 /* Static buffers */
 
-/**
- * struct udp_payload_t - UDP header and data for inbound messages
- * @uh:		UDP header
- * @data:	UDP data
- */
-static struct udp_payload_t {
-	struct udphdr uh;
-	char data[USHRT_MAX - sizeof(struct udphdr)];
-#ifdef __AVX2__
-} __attribute__ ((packed, aligned(32)))
-#else
-} __attribute__ ((packed, aligned(__alignof__(unsigned int))))
-#endif
-udp_payload[UDP_MAX_FRAMES];
+/* UDP header and data for inbound messages */
+static struct udp_payload_t udp_payload[UDP_MAX_FRAMES];
 
 /* Ethernet header for IPv4 frames */
 static struct ethhdr udp4_eth_hdr;
@@ -311,6 +298,7 @@ static void udp_splice_send(const struct ctx *c, size_t start, size_t n,
 
 /**
  * udp_update_hdr4() - Update headers for one IPv4 datagram
+ * @c:		Execution context
  * @ip4h:	Pre-filled IPv4 header (except for tot_len and saddr)
  * @bp:		Pointer to udp_payload_t to update
  * @toside:	Flowside for destination side
@@ -318,8 +306,9 @@ static void udp_splice_send(const struct ctx *c, size_t start, size_t n,
  *
  * Return: size of IPv4 payload (UDP header + data)
  */
-static size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp,
-			      const struct flowside *toside, size_t dlen)
+size_t udp_update_hdr4(const struct ctx *c,
+		       struct iphdr *ip4h, struct udp_payload_t *bp,
+		       const struct flowside *toside, size_t dlen)
 {
 	const struct in_addr *src = inany_v4(&toside->faddr);
 	const struct in_addr *dst = inany_v4(&toside->eaddr);
@@ -336,13 +325,17 @@ static size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp,
 	bp->uh.source = htons(toside->fport);
 	bp->uh.dest = htons(toside->eport);
 	bp->uh.len = htons(l4len);
-	csum_udp4(&bp->uh, *src, *dst, bp->data, dlen);
+	if (c->mode != MODE_VU)
+		csum_udp4(&bp->uh, *src, *dst, bp->data, dlen);
+	else
+		bp->uh.check = 0;
 
 	return l4len;
 }
 
 /**
  * udp_update_hdr6() - Update headers for one IPv6 datagram
+ * @c:		Execution context
  * @ip6h:	Pre-filled IPv6 header (except for payload_len and addresses)
  * @bp:		Pointer to udp_payload_t to update
  * @toside:	Flowside for destination side
@@ -350,8 +343,9 @@ static size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp,
  *
  * Return: size of IPv6 payload (UDP header + data)
  */
-static size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp,
-			      const struct flowside *toside, size_t dlen)
+size_t udp_update_hdr6(const struct ctx *c,
+		       struct ipv6hdr *ip6h, struct udp_payload_t *bp,
+		       const struct flowside *toside, size_t dlen)
 {
 	uint16_t l4len = dlen + sizeof(bp->uh);
 
@@ -365,19 +359,24 @@ static size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp,
 	bp->uh.source = htons(toside->fport);
 	bp->uh.dest = htons(toside->eport);
 	bp->uh.len = ip6h->payload_len;
-	csum_udp6(&bp->uh, &toside->faddr.a6, &toside->eaddr.a6, bp->data, dlen);
+	if (c->mode != MODE_VU)
+		csum_udp6(&bp->uh, &toside->faddr.a6, &toside->eaddr.a6,
+			  bp->data, dlen);
+	else
+		bp->uh.check = 0xffff; /* zero checksum is invalid with IPv6 */
 
 	return l4len;
 }
 
 /**
  * udp_tap_prepare() - Convert one datagram into a tap frame
+ * @c:		Execution context
  * @mmh:	Receiving mmsghdr array
  * @idx:	Index of the datagram to prepare
  * @toside:	Flowside for destination side
  */
-static void udp_tap_prepare(const struct mmsghdr *mmh, unsigned idx,
-			    const struct flowside *toside)
+static void udp_tap_prepare(const struct ctx *c, const struct mmsghdr *mmh,
+			    unsigned idx, const struct flowside *toside)
 {
 	struct iovec (*tap_iov)[UDP_NUM_IOVS] = &udp_l2_iov[idx];
 	struct udp_payload_t *bp = &udp_payload[idx];
@@ -385,13 +384,15 @@ static void udp_tap_prepare(const struct mmsghdr *mmh, unsigned idx,
 	size_t l4len;
 
 	if (!inany_v4(&toside->eaddr) || !inany_v4(&toside->faddr)) {
-		l4len = udp_update_hdr6(&bm->ip6h, bp, toside, mmh[idx].msg_len);
+		l4len = udp_update_hdr6(c, &bm->ip6h, bp, toside,
+					mmh[idx].msg_len);
 		tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip6h) +
 			       sizeof(udp6_eth_hdr));
 		(*tap_iov)[UDP_IOV_ETH] = IOV_OF_LVALUE(udp6_eth_hdr);
 		(*tap_iov)[UDP_IOV_IP] = IOV_OF_LVALUE(bm->ip6h);
 	} else {
-		l4len = udp_update_hdr4(&bm->ip4h, bp, toside, mmh[idx].msg_len);
+		l4len = udp_update_hdr4(c, &bm->ip4h, bp, toside,
+					mmh[idx].msg_len);
 		tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip4h) +
 			       sizeof(udp4_eth_hdr));
 		(*tap_iov)[UDP_IOV_ETH] = IOV_OF_LVALUE(udp4_eth_hdr);
@@ -408,7 +409,7 @@ static void udp_tap_prepare(const struct mmsghdr *mmh, unsigned idx,
  *
  * #syscalls recvmsg
  */
-static bool udp_sock_recverr(int s)
+bool udp_sock_recverr(int s)
 {
 	const struct sock_extended_err *ee;
 	const struct cmsghdr *hdr;
@@ -495,7 +496,7 @@ static int udp_sock_recv(const struct ctx *c, int s, uint32_t events,
 }
 
 /**
- * udp_listen_sock_handler() - Handle new data from socket
+ * udp_buf_listen_sock_handler() - Handle new data from socket
  * @c:		Execution context
  * @ref:	epoll reference
  * @events:	epoll events bitmap
@@ -503,8 +504,8 @@ static int udp_sock_recv(const struct ctx *c, int s, uint32_t events,
  *
  * #syscalls recvmmsg
  */
-void udp_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
-			     uint32_t events, const struct timespec *now)
+void udp_buf_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
+				 uint32_t events, const struct timespec *now)
 {
 	struct mmsghdr *mmh_recv = ref.udp.v6 ? udp6_mh_recv : udp4_mh_recv;
 	int n, i;
@@ -527,7 +528,7 @@ void udp_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
 			if (pif_is_socket(batchpif)) {
 				udp_splice_prepare(mmh_recv, i);
 			} else if (batchpif == PIF_TAP) {
-				udp_tap_prepare(mmh_recv, i,
+				udp_tap_prepare(c, mmh_recv, i,
 						flowside_at_sidx(batchsidx));
 			}
 
@@ -561,7 +562,7 @@ void udp_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
 }
 
 /**
- * udp_reply_sock_handler() - Handle new data from flow specific socket
+ * udp_buf_reply_sock_handler() - Handle new data from flow specific socket
  * @c:		Execution context
  * @ref:	epoll reference
  * @events:	epoll events bitmap
@@ -569,8 +570,8 @@ void udp_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
  *
  * #syscalls recvmmsg
  */
-void udp_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
-			    uint32_t events, const struct timespec *now)
+void udp_buf_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
+				uint32_t events, const struct timespec *now)
 {
 	const struct flowside *fromside = flowside_at_sidx(ref.flowside);
 	flow_sidx_t tosidx = flow_sidx_opposite(ref.flowside);
@@ -594,7 +595,7 @@ void udp_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
 		if (pif_is_socket(topif))
 			udp_splice_prepare(mmh_recv, i);
 		else if (topif == PIF_TAP)
-			udp_tap_prepare(mmh_recv, i, toside);
+			udp_tap_prepare(c, mmh_recv, i, toside);
 	}
 
 	if (pif_is_socket(topif)) {
diff --git a/udp.h b/udp.h
index fb42e1c50d70..77b29260e8d1 100644
--- a/udp.h
+++ b/udp.h
@@ -9,10 +9,10 @@
 #define UDP_TIMER_INTERVAL		1000 /* ms */
 
 void udp_portmap_clear(void);
-void udp_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
-			     uint32_t events, const struct timespec *now);
-void udp_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
-			    uint32_t events, const struct timespec *now);
+void udp_buf_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
+				 uint32_t events, const struct timespec *now);
+void udp_buf_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
+				uint32_t events, const struct timespec *now);
 int udp_tap_handler(const struct ctx *c, uint8_t pif,
 		    sa_family_t af, const void *saddr, const void *daddr,
 		    const struct pool *p, int idx, const struct timespec *now);
diff --git a/udp_internal.h b/udp_internal.h
new file mode 100644
index 000000000000..7dd45753698f
--- /dev/null
+++ b/udp_internal.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright (c) 2021 Red Hat GmbH
+ * Author: Stefano Brivio <sbrivio@redhat.com>
+ */
+
+#ifndef UDP_INTERNAL_H
+#define UDP_INTERNAL_H
+
+#include "tap.h" /* needed by udp_meta_t */
+
+#define UDP_MAX_FRAMES		32  /* max # of frames to receive at once */
+
+/**
+ * struct udp_payload_t - UDP header and data for inbound messages
+ * @uh:		UDP header
+ * @data:	UDP data
+ */
+struct udp_payload_t {
+	struct udphdr uh;
+	char data[USHRT_MAX - sizeof(struct udphdr)];
+#ifdef __AVX2__
+} __attribute__ ((packed, aligned(32)));
+#else
+} __attribute__ ((packed, aligned(__alignof__(unsigned int))));
+#endif
+
+size_t udp_update_hdr4(const struct ctx *c,
+		       struct iphdr *ip4h, struct udp_payload_t *bp,
+		       const struct flowside *toside, size_t dlen);
+size_t udp_update_hdr6(const struct ctx *c,
+                       struct ipv6hdr *ip6h, struct udp_payload_t *bp,
+                       const struct flowside *toside, size_t dlen);
+bool udp_sock_recverr(int s);
+#endif /* UDP_INTERNAL_H */
diff --git a/udp_vu.c b/udp_vu.c
new file mode 100644
index 000000000000..f9e7afcf4ddb
--- /dev/null
+++ b/udp_vu.c
@@ -0,0 +1,338 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: Laurent Vivier <lvivier@redhat.com>
+ *
+ * udp_vu.c - UDP L2 vhost-user management functions
+ */
+
+#include <unistd.h>
+#include <assert.h>
+#include <net/ethernet.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/udp.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <sys/uio.h>
+#include <linux/virtio_net.h>
+
+#include "checksum.h"
+#include "util.h"
+#include "ip.h"
+#include "siphash.h"
+#include "inany.h"
+#include "passt.h"
+#include "pcap.h"
+#include "log.h"
+#include "vhost_user.h"
+#include "udp_internal.h"
+#include "flow.h"
+#include "flow_table.h"
+#include "udp_flow.h"
+#include "udp_vu.h"
+#include "vu_common.h"
+
+/* vhost-user */
+static const struct virtio_net_hdr vu_header = {
+	.flags = VIRTIO_NET_HDR_F_DATA_VALID,
+	.gso_type = VIRTIO_NET_HDR_GSO_NONE,
+};
+
+static struct iovec     iov_vu		[VIRTQUEUE_MAX_SIZE];
+static struct vu_virtq_element	elem		[VIRTQUEUE_MAX_SIZE];
+static struct iovec in_sg[VIRTQUEUE_MAX_SIZE];
+static int in_sg_count;
+
+static size_t udp_vu_l2_hdrlen(const struct vu_dev *vdev, bool v6)
+{
+	size_t l2_hdrlen;
+
+	l2_hdrlen = vdev->hdrlen + sizeof(struct ethhdr) +
+		    sizeof(struct udphdr);
+
+	if (v6)
+		l2_hdrlen += sizeof(struct ipv6hdr);
+	else
+		l2_hdrlen += sizeof(struct iphdr);
+
+	return l2_hdrlen;
+}
+
+static int udp_vu_sock_recv(const struct ctx *c, union sockaddr_inany *s_in,
+			    int s, uint32_t events, bool v6, ssize_t *data_len)
+{
+	struct vu_dev *vdev = c->vdev;
+	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
+	int virtqueue_max, iov_cnt, idx, iov_used;
+	size_t fillsize, size, off, l2_hdrlen;
+	struct virtio_net_hdr_mrg_rxbuf *vh;
+	struct msghdr msg  = { 0 };
+	char *base;
+
+	ASSERT(!c->no_udp);
+
+	/* Clear any errors first */
+	if (events & EPOLLERR) {
+		while (udp_sock_recverr(s))
+			;
+	}
+
+	if (!(events & EPOLLIN))
+		return 0;
+
+	/* compute L2 header length */
+
+	if (vu_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
+		virtqueue_max = VIRTQUEUE_MAX_SIZE;
+	else
+		virtqueue_max = 1;
+
+	l2_hdrlen = udp_vu_l2_hdrlen(vdev, v6);
+
+	msg.msg_name = s_in;
+	msg.msg_namelen = sizeof(union sockaddr_inany);
+
+	fillsize = USHRT_MAX;
+	iov_cnt = 0;
+	in_sg_count = 0;
+	while (fillsize && iov_cnt < virtqueue_max &&
+			in_sg_count < ARRAY_SIZE(in_sg)) {
+		int ret;
+
+		elem[iov_cnt].out_num = 0;
+		elem[iov_cnt].out_sg = NULL;
+		elem[iov_cnt].in_num = ARRAY_SIZE(in_sg) - in_sg_count;
+		elem[iov_cnt].in_sg = &in_sg[in_sg_count];
+		ret = vu_queue_pop(vdev, vq, &elem[iov_cnt]);
+		if (ret < 0)
+			break;
+		in_sg_count += elem[iov_cnt].in_num;
+
+		if (elem[iov_cnt].in_num < 1) {
+			err("virtio-net receive queue contains no in buffers");
+			vu_queue_rewind(vq, iov_cnt);
+			return 0;
+		}
+		ASSERT(elem[iov_cnt].in_num == 1);
+		ASSERT(elem[iov_cnt].in_sg[0].iov_len >= l2_hdrlen);
+
+		if (iov_cnt == 0) {
+			base = elem[iov_cnt].in_sg[0].iov_base;
+			size = elem[iov_cnt].in_sg[0].iov_len;
+
+			/* keep space for the headers */
+			iov_vu[0].iov_base = base + l2_hdrlen;
+			iov_vu[0].iov_len = size - l2_hdrlen;
+		} else {
+			iov_vu[iov_cnt].iov_base = elem[iov_cnt].in_sg[0].iov_base;
+			iov_vu[iov_cnt].iov_len = elem[iov_cnt].in_sg[0].iov_len;
+		}
+
+		if (iov_vu[iov_cnt].iov_len > fillsize)
+			iov_vu[iov_cnt].iov_len = fillsize;
+
+		fillsize -= iov_vu[iov_cnt].iov_len;
+
+		iov_cnt++;
+	}
+	if (iov_cnt == 0)
+		return 0;
+
+	msg.msg_iov = iov_vu;
+	msg.msg_iovlen = iov_cnt;
+
+	*data_len = recvmsg(s, &msg, 0);
+	if (*data_len < 0) {
+		vu_queue_rewind(vq, iov_cnt);
+		return 0;
+	}
+
+	/* restore original values */
+	iov_vu[0].iov_base = base;
+	iov_vu[0].iov_len = size;
+
+	/* count the numbers of buffer filled by recvmsg() */
+	idx = iov_skip_bytes(iov_vu, iov_cnt, l2_hdrlen + *data_len,
+			     &off);
+	/* adjust last iov length */
+	if (idx < iov_cnt)
+		iov_vu[idx].iov_len = off;
+	iov_used = idx + !!off;
+
+	/* release unused buffers */
+	vu_queue_rewind(vq, iov_cnt - iov_used);
+
+	vh = (struct virtio_net_hdr_mrg_rxbuf *)base;
+	vh->hdr = vu_header;
+	if (vdev->hdrlen == sizeof(struct virtio_net_hdr_mrg_rxbuf))
+		vh->num_buffers = htole16(iov_used);
+
+	return iov_used;
+}
+
+static size_t udp_vu_prepare(const struct ctx *c,
+			     const struct flowside *toside, ssize_t data_len)
+{
+	const struct vu_dev *vdev = c->vdev;
+	struct ethhdr *eh;
+	size_t l4len;
+
+	/* ethernet header */
+	eh = vu_eth(vdev, iov_vu[0].iov_base);
+
+	memcpy(eh->h_dest, c->mac_guest, sizeof(eh->h_dest));
+	memcpy(eh->h_source, c->mac, sizeof(eh->h_source));
+
+	/* initialize header */
+	if (inany_v4(&toside->eaddr) && inany_v4(&toside->faddr)) {
+		struct iphdr *iph = vu_ip(vdev, iov_vu[0].iov_base);
+		struct udp_payload_t *bp = vu_payloadv4(vdev,
+							    iov_vu[0].iov_base);
+
+		eh->h_proto = htons(ETH_P_IP);
+
+		*iph = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_UDP);
+
+		l4len = udp_update_hdr4(c, iph, bp, toside, data_len);
+	} else {
+		struct ipv6hdr *ip6h = vu_ip(vdev, iov_vu[0].iov_base);
+		struct udp_payload_t *bp = vu_payloadv6(vdev,
+							    iov_vu[0].iov_base);
+
+		eh->h_proto = htons(ETH_P_IPV6);
+
+		*ip6h = (struct ipv6hdr)L2_BUF_IP6_INIT(IPPROTO_UDP);
+
+		l4len = udp_update_hdr6(c, ip6h, bp, toside, data_len);
+	}
+
+	return l4len;
+}
+
+static void udp_vu_pcap(const struct ctx *c, const struct flowside *toside,
+			size_t l4len, int iov_used)
+{
+	const struct in_addr *src = inany_v4(&toside->faddr);
+	const struct in_addr *dst = inany_v4(&toside->eaddr);
+	const struct vu_dev *vdev = c->vdev;
+	char *base = iov_vu[0].iov_base;
+	size_t size = iov_vu[0].iov_len;
+	struct udp_payload_t *bp;
+	uint32_t sum;
+
+	if (!*c->pcap)
+		return;
+
+	if (src && dst) {
+		bp = vu_payloadv4(vdev, base);
+		sum = proto_ipv4_header_psum(l4len, IPPROTO_UDP, *src, *dst);
+	} else {
+		bp = vu_payloadv6(vdev, base);
+		sum = proto_ipv6_header_psum(l4len, IPPROTO_UDP,
+					     &toside->faddr.a6,
+					     &toside->eaddr.a6);
+		bp->uh.check = 0; /* by default, set to 0xffff */
+	}
+
+	iov_vu[0].iov_base = &bp->uh;
+	iov_vu[0].iov_len = size - ((char *)iov_vu[0].iov_base - base);
+
+	bp->uh.check = csum_iov(iov_vu, iov_used, sum);
+
+	/* set iov for pcap logging */
+	iov_vu[0].iov_base = base + vdev->hdrlen;
+	iov_vu[0].iov_len = size - vdev->hdrlen;
+	pcap_iov(iov_vu, iov_used);
+
+	/* restore iov_vu[0] */
+	iov_vu[0].iov_base = base;
+	iov_vu[0].iov_len = size;
+}
+
+void udp_vu_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
+				uint32_t events, const struct timespec *now)
+{
+	struct vu_dev *vdev = c->vdev;
+	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
+	bool v6 = ref.udp.v6;
+	int i;
+
+	for (i = 0; i < UDP_MAX_FRAMES; i++) {
+		union sockaddr_inany s_in;
+		flow_sidx_t batchsidx;
+		uint8_t batchpif;
+		ssize_t data_len;
+		int iov_used;
+
+		iov_used = udp_vu_sock_recv(c, &s_in, ref.fd,
+					    events, v6, &data_len);
+		if (iov_used <= 0)
+			return;
+
+		batchsidx = udp_flow_from_sock(c, ref, &s_in, now);
+		batchpif = pif_at_sidx(batchsidx);
+
+		if (batchpif == PIF_TAP) {
+			size_t l4len;
+
+			l4len = udp_vu_prepare(c, flowside_at_sidx(batchsidx),
+					       data_len);
+			udp_vu_pcap(c, flowside_at_sidx(batchsidx), l4len,
+				    iov_used);
+			vu_send_frame(vdev, vq, elem, iov_vu, iov_used);
+		} else if (flow_sidx_valid(batchsidx)) {
+			flow_sidx_t fromsidx = flow_sidx_opposite(batchsidx);
+			struct udp_flow *uflow = udp_at_sidx(batchsidx);
+
+			flow_err(uflow,
+				 "No support for forwarding UDP from %s to %s",
+				 pif_name(pif_at_sidx(fromsidx)),
+				 pif_name(batchpif));
+		} else {
+			debug("Discarding 1 datagram without flow");
+		}
+	}
+}
+
+void udp_vu_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
+			        uint32_t events, const struct timespec *now)
+{
+	flow_sidx_t tosidx = flow_sidx_opposite(ref.flowside);
+	const struct flowside *toside = flowside_at_sidx(tosidx);
+	struct vu_dev *vdev = c->vdev;
+	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
+	struct udp_flow *uflow = udp_at_sidx(ref.flowside);
+	uint8_t topif = pif_at_sidx(tosidx);
+	bool v6 = ref.udp.v6;
+	int i;
+
+	ASSERT(!c->no_udp && uflow);
+
+	for (i = 0; i < UDP_MAX_FRAMES; i++) {
+		union sockaddr_inany s_in;
+		ssize_t data_len;
+		int iov_used;
+
+		iov_used = udp_vu_sock_recv(c, &s_in, ref.fd,
+					    events, v6, &data_len);
+		if (iov_used <= 0)
+			return;
+		flow_trace(uflow, "Received 1 datagram on reply socket");
+		uflow->ts = now->tv_sec;
+
+		if (topif == PIF_TAP) {
+			size_t l4len;
+
+			l4len = udp_vu_prepare(c, toside, data_len);
+			udp_vu_pcap(c, toside, l4len, iov_used);
+			vu_send_frame(vdev, vq, elem, iov_vu, iov_used);
+		} else {
+			uint8_t frompif = pif_at_sidx(ref.flowside);
+
+			flow_err(uflow,
+				 "No support for forwarding UDP from %s to %s",
+				 pif_name(frompif), pif_name(topif));
+		}
+	}
+}
diff --git a/udp_vu.h b/udp_vu.h
new file mode 100644
index 000000000000..0db7558914d9
--- /dev/null
+++ b/udp_vu.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: Laurent Vivier <lvivier@redhat.com>
+ */
+
+#ifndef UDP_VU_H
+#define UDP_VU_H
+
+void udp_vu_listen_sock_handler(const struct ctx *c, union epoll_ref ref,
+				uint32_t events, const struct timespec *now);
+void udp_vu_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
+			       uint32_t events, const struct timespec *now);
+#endif /* UDP_VU_H */
diff --git a/vhost_user.c b/vhost_user.c
index c4cd25fae84e..e65b550774b7 100644
--- a/vhost_user.c
+++ b/vhost_user.c
@@ -52,7 +52,6 @@
  * 			     this is part of the vhost-user backend
  * 			     convention.
  */
-/* cppcheck-suppress unusedFunction */
 void vu_print_capabilities(void)
 {
 	info("{");
@@ -163,8 +162,7 @@ static void vmsg_close_fds(const struct vhost_user_msg *vmsg)
  */
 static void vu_remove_watch(const struct vu_dev *vdev, int fd)
 {
-	(void)vdev;
-	(void)fd;
+	epoll_ctl(vdev->context->epollfd, EPOLL_CTL_DEL, fd, NULL);
 }
 
 /**
@@ -426,7 +424,6 @@ static bool map_ring(struct vu_dev *vdev, struct vu_virtq *vq)
  *
  * Return: 0 if the zone in a mapped memory region, -1 otherwise
  */
-/* cppcheck-suppress unusedFunction */
 int vu_packet_check_range(void *buf, size_t offset, size_t len,
 			  const char *start)
 {
@@ -517,6 +514,14 @@ static bool vu_set_mem_table_exec(struct vu_dev *vdev,
 		}
 	}
 
+	/* As vu_packet_check_range() has no access to the number of
+	 * memory regions, mark the end of the array with mmap_addr = 0
+	 */
+	ASSERT(vdev->nregions < VHOST_USER_MAX_RAM_SLOTS - 1);
+	vdev->regions[vdev->nregions].mmap_addr = 0;
+
+	tap_sock_update_buf(vdev->regions, 0);
+
 	return false;
 }
 
@@ -637,8 +642,12 @@ static bool vu_get_vring_base_exec(struct vu_dev *vdev,
  */
 static void vu_set_watch(const struct vu_dev *vdev, int fd)
 {
-	(void)vdev;
-	(void)fd;
+	union epoll_ref ref = { .type = EPOLL_TYPE_VHOST_KICK, .fd = fd };
+	struct epoll_event ev = { 0 };
+
+	ev.data.u64 = ref.u64;
+	ev.events = EPOLLIN;
+	epoll_ctl(vdev->context->epollfd, EPOLL_CTL_ADD, fd, &ev);
 }
 
 /**
@@ -678,7 +687,6 @@ static int vu_wait_queue(const struct vu_virtq *vq)
  *
  * Return: number of bytes sent, -1 if there is an error
  */
-/* cppcheck-suppress unusedFunction */
 int vu_send(struct vu_dev *vdev, const void *buf, size_t size)
 {
 	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
@@ -864,7 +872,6 @@ static void vu_handle_tx(struct vu_dev *vdev, int index,
  * @vdev:	vhost-user device
  * @ref:	epoll reference information
  */
-/* cppcheck-suppress unusedFunction */
 void vu_kick_cb(struct vu_dev *vdev, union epoll_ref ref,
 		const struct timespec *now)
 {
@@ -1102,11 +1109,11 @@ static bool vu_set_vring_enable_exec(struct vu_dev *vdev,
  * @c:		execution context
  * @vdev:	vhost-user device
  */
-/* cppcheck-suppress unusedFunction */
 void vu_init(struct ctx *c, struct vu_dev *vdev)
 {
 	int i;
 
+	c->vdev = vdev;
 	vdev->context = c;
 	vdev->hdrlen = 0;
 	for (i = 0; i < VHOST_USER_MAX_QUEUES; i++) {
@@ -1170,7 +1177,7 @@ void vu_cleanup(struct vu_dev *vdev)
  */
 static void vu_sock_reset(struct vu_dev *vdev)
 {
-	(void)vdev;
+	tap_sock_reset(vdev->context);
 }
 
 /**
@@ -1179,7 +1186,6 @@ static void vu_sock_reset(struct vu_dev *vdev)
  * @fd:		vhost-user message socket
  * @events:	epoll events
  */
-/* cppcheck-suppress unusedFunction */
 void tap_handler_vu(struct vu_dev *vdev, int fd, uint32_t events)
 {
 	struct vhost_user_msg msg = { 0 };
diff --git a/virtio.c b/virtio.c
index d02e6e04701d..55fc647842bb 100644
--- a/virtio.c
+++ b/virtio.c
@@ -559,7 +559,6 @@ void vu_queue_unpop(struct vu_virtq *vq)
  * @vq:		Virtqueue
  * @num:	Number of element to unpop
  */
-/* cppcheck-suppress unusedFunction */
 bool vu_queue_rewind(struct vu_virtq *vq, unsigned int num)
 {
 	if (num > vq->inuse)
diff --git a/vu_common.c b/vu_common.c
new file mode 100644
index 000000000000..611c44a39142
--- /dev/null
+++ b/vu_common.c
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: Laurent Vivier <lvivier@redhat.com>
+ *
+ * common_vu.c - vhost-user common UDP and TCP functions
+ */
+
+#include <unistd.h>
+#include <sys/uio.h>
+
+#include "util.h"
+#include "passt.h"
+#include "vhost_user.h"
+#include "vu_common.h"
+
+void vu_send_frame(const struct vu_dev *vdev, struct vu_virtq *vq,
+		   struct vu_virtq_element *elem, const struct iovec *iov_vu,
+		   int iov_used)
+{
+	int i;
+
+	for (i = 0; i < iov_used; i++)
+		vu_queue_fill(vq, &elem[i], iov_vu[i].iov_len, i);
+
+	vu_queue_flush(vq, iov_used);
+	vu_queue_notify(vdev, vq);
+}
diff --git a/vu_common.h b/vu_common.h
new file mode 100644
index 000000000000..d2ea46bd379b
--- /dev/null
+++ b/vu_common.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: Laurent Vivier <lvivier@redhat.com>
+ *
+ * vhost-user common UDP and TCP functions
+ */
+
+#ifndef VU_COMMON_H
+#define VU_COMMON_H
+
+static inline void *vu_eth(const struct vu_dev *vdev, void *base)
+{
+	return ((char *)base + vdev->hdrlen);
+}
+
+static inline void *vu_ip(const struct vu_dev *vdev, void *base)
+{
+	return (struct ethhdr *)vu_eth(vdev, base) + 1;
+}
+
+static inline void *vu_payloadv4(const struct vu_dev *vdev, void *base)
+{
+	return (struct iphdr *)vu_ip(vdev, base) + 1;
+}
+
+static inline void *vu_payloadv6(const struct vu_dev *vdev, void *base)
+{
+	return (struct ipv6hdr *)vu_ip(vdev, base) + 1;
+}
+
+void vu_send_frame(const struct vu_dev *vdev, struct vu_virtq *vq,
+		   struct vu_virtq_element *elem, const struct iovec *iov_vu,
+		   int iov_used);
+#endif /* VU_COMMON_H */
-- 
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: Laurent Vivier <lvivier@redhat.com>
+ *
+ * vhost-user common UDP and TCP functions
+ */
+
+#ifndef VU_COMMON_H
+#define VU_COMMON_H
+
+static inline void *vu_eth(const struct vu_dev *vdev, void *base)
+{
+	return ((char *)base + vdev->hdrlen);
+}
+
+static inline void *vu_ip(const struct vu_dev *vdev, void *base)
+{
+	return (struct ethhdr *)vu_eth(vdev, base) + 1;
+}
+
+static inline void *vu_payloadv4(const struct vu_dev *vdev, void *base)
+{
+	return (struct iphdr *)vu_ip(vdev, base) + 1;
+}
+
+static inline void *vu_payloadv6(const struct vu_dev *vdev, void *base)
+{
+	return (struct ipv6hdr *)vu_ip(vdev, base) + 1;
+}
+
+void vu_send_frame(const struct vu_dev *vdev, struct vu_virtq *vq,
+		   struct vu_virtq_element *elem, const struct iovec *iov_vu,
+		   int iov_used);
+#endif /* VU_COMMON_H */
-- 
2.45.2