@@ -124,6 +124,6 @@ $(OUTPUT)/reuseport_bpf_numa: LDLIBS += -lnuma
 $(OUTPUT)/tcp_mmap: LDLIBS += -lpthread -lcrypto
 $(OUTPUT)/tcp_inq: LDLIBS += -lpthread
 $(OUTPUT)/bind_bhash: LDLIBS += -lpthread
-$(OUTPUT)/io_uring_zerocopy_tx: CFLAGS += -I../../../include/
+$(OUTPUT)/io_uring_zerocopy_tx $(OUTPUT)/tun: CFLAGS += -I../../../include/
 
 include bpf.mk

@@ -2,22 +2,38 @@
 
 #define _GNU_SOURCE
 
+#include <endian.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <sched.h>
+#include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <linux/if.h>
+#include <net/if.h>
+#include <netinet/ip.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <linux/compiler.h>
+#include <linux/icmp.h>
+#include <linux/if_arp.h>
 #include <linux/if_tun.h>
+#include <linux/ipv6.h>
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>
+#include <linux/sockios.h>
+#include <linux/tcp.h>
+#include <linux/udp.h>
 #include <linux/virtio_net.h>
-#include <sys/ioctl.h>
-#include <sys/socket.h>
 
 #include "../kselftest_harness.h"
 
+#define TUN_HWADDR_SOURCE { 0x02, 0x00, 0x00, 0x00, 0x00, 0x00 }
+#define TUN_HWADDR_DEST { 0x02, 0x00, 0x00, 0x00, 0x00, 0x01 }
+#define TUN_IPADDR_SOURCE htonl((172 << 24) | (17 << 16) | 0)
+#define TUN_IPADDR_DEST htonl((172 << 24) | (17 << 16) | 1)
+
 static int tun_attach(int fd, char *dev)
 {
 	struct ifreq ifr;

@@ -40,7 +56,7 @@ static int tun_detach(int fd, char *dev)
 	return ioctl(fd, TUNSETQUEUE, (void *) &ifr);
 }
 
-static int tun_alloc(char *dev)
+static int tun_alloc(char *dev, short flags)
 {
 	struct ifreq ifr;
 	int fd, err;

@@ -53,7 +69,8 @@ static int tun_alloc(char *dev)
 
 	memset(&ifr, 0, sizeof(ifr));
 	strcpy(ifr.ifr_name, dev);
-	ifr.ifr_flags = IFF_TAP | IFF_NAPI | IFF_MULTI_QUEUE;
+	ifr.ifr_flags = flags | IFF_TAP | IFF_NAPI | IFF_NO_PI |
+			IFF_MULTI_QUEUE;
 
 	err = ioctl(fd, TUNSETIFF, (void *) &ifr);
 	if (err < 0) {

@@ -65,6 +82,20 @@ static int tun_alloc(char *dev)
 	return fd;
 }
 
+static bool tun_set_flags(int local_fd, const char *name, short flags)
+{
+	struct ifreq ifreq = { .ifr_flags = flags };
+
+	strcpy(ifreq.ifr_name, name);
+
+	if (ioctl(local_fd, SIOCSIFFLAGS, &ifreq)) {
+		perror("SIOCSIFFLAGS");
+		return false;
+	}
+
+	return true;
+}
+
 static int tun_delete(char *dev)
 {
 	struct {

@@ -103,6 +134,107 @@ static int tun_delete(char *dev)
 	return ret;
 }
 
+static uint32_t tun_sum(const void *buf, size_t len)
+{
+	const uint16_t *sbuf = buf;
+	uint32_t sum = 0;
+
+	while (len > 1) {
+		sum += *sbuf++;
+		len -= 2;
+	}
+
+	if (len)
+		sum += *(uint8_t *)sbuf;
+
+	return sum;
+}
+
+static uint16_t tun_build_ip_check(uint32_t sum)
+{
+	return ~((sum & 0xffff) + (sum >> 16));
+}
+
+static uint32_t tun_build_ip_pseudo_sum(const void *iphdr)
+{
+	uint16_t tot_len = ntohs(((struct iphdr *)iphdr)->tot_len);
+
+	return tun_sum((char *)iphdr + offsetof(struct iphdr, saddr), 8) +
+	       htons(((struct iphdr *)iphdr)->protocol) +
+	       htons(tot_len - sizeof(struct iphdr));
+}
+
+static uint32_t tun_build_ipv6_pseudo_sum(const void *ipv6hdr)
+{
+	return tun_sum((char *)ipv6hdr + offsetof(struct ipv6hdr, saddr), 32) +
+	       ((struct ipv6hdr *)ipv6hdr)->payload_len +
+	       htons(((struct ipv6hdr *)ipv6hdr)->nexthdr);
+}
+
+static void tun_build_iphdr(void *dest, uint16_t len, uint8_t protocol)
+{
+	struct iphdr iphdr = {
+		.ihl = sizeof(iphdr) / 4,
+		.version = 4,
+		.tot_len = htons(sizeof(iphdr) + len),
+		.ttl = 255,
+		.protocol = protocol,
+		.saddr = TUN_IPADDR_SOURCE,
+		.daddr = TUN_IPADDR_DEST
+	};
+
+	iphdr.check = tun_build_ip_check(tun_sum(&iphdr, sizeof(iphdr)));
+	memcpy(dest, &iphdr, sizeof(iphdr));
+}
+
+static void tun_build_ipv6hdr(void *dest, uint16_t len, uint8_t protocol)
+{
+	struct ipv6hdr ipv6hdr = {
+		.version = 6,
+		.payload_len = htons(len),
+		.nexthdr = protocol,
+		.saddr = {
+			.s6_addr32 = {
+				htonl(0xffff0000), 0, 0, TUN_IPADDR_SOURCE
+			}
+		},
+		.daddr = {
+			.s6_addr32 = {
+				htonl(0xffff0000), 0, 0, TUN_IPADDR_DEST
+			}
+		},
+	};
+
+	memcpy(dest, &ipv6hdr, sizeof(ipv6hdr));
+}
+
+static void tun_build_tcphdr(void *dest, uint32_t sum)
+{
+	struct tcphdr tcphdr = {
+		.source = htons(9),
+		.dest = htons(9),
+		.fin = 1,
+		.doff = sizeof(tcphdr) / 4,
+	};
+	uint32_t tcp_sum = tun_sum(&tcphdr, sizeof(tcphdr));
+
+	tcphdr.check = tun_build_ip_check(sum + tcp_sum);
+	memcpy(dest, &tcphdr, sizeof(tcphdr));
+}
+
+static void tun_build_udphdr(void *dest, uint32_t sum)
+{
+	struct udphdr udphdr = {
+		.source = htons(9),
+		.dest = htons(9),
+		.len = htons(sizeof(udphdr)),
+	};
+	uint32_t udp_sum = tun_sum(&udphdr, sizeof(udphdr));
+
+	udphdr.check = tun_build_ip_check(sum + udp_sum);
+	memcpy(dest, &udphdr, sizeof(udphdr));
+}
+
 FIXTURE(tun)
 {
 	char ifname[IFNAMSIZ];

@@ -113,10 +245,10 @@ FIXTURE_SETUP(tun)
 {
 	memset(self->ifname, 0, sizeof(self->ifname));
 
-	self->fd = tun_alloc(self->ifname);
+	self->fd = tun_alloc(self->ifname, 0);
 	ASSERT_GE(self->fd, 0);
 
-	self->fd2 = tun_alloc(self->ifname);
+	self->fd2 = tun_alloc(self->ifname, 0);
 	ASSERT_GE(self->fd2, 0);
 }
 

@@ -169,7 +301,7 @@ FIXTURE(tun_deleted)
 FIXTURE_SETUP(tun_deleted)
 {
 	self->ifname[0] = 0;
-	self->fd = tun_alloc(self->ifname);
+	self->fd = tun_alloc(self->ifname, 0);
 	ASSERT_LE(0, self->fd);
 
 	ASSERT_EQ(0, tun_delete(self->ifname))

@@ -198,4 +330,302 @@ TEST_F(tun_deleted, getvnethashtypes)
 	EXPECT_FALSE(ret);
 }
 
-TEST_HARNESS_MAIN
+FIXTURE(tun_vnet_rss)
+{
+	int dest_fds[3];
+	unsigned int dest_ifindex;
+	int source_fd;
+	char buffer[sizeof(struct ipv6hdr) + sizeof(struct tcphdr)];
+	uint16_t len;
+};
+
+FIXTURE_VARIANT(tun_vnet_rss)
+{
+	uint16_t eth_p;
+	uint8_t ipproto;
+	uint8_t flags;
+	uint16_t hash_report;
+	uint32_t hash_value;
+};
+
+FIXTURE_VARIANT_ADD(tun_vnet_rss, unclassified)
+{
+	.eth_p = ETH_P_LOOPBACK
+};
+
+FIXTURE_VARIANT_ADD(tun_vnet_rss, ipv4)
+{
+	.eth_p = ETH_P_IP,
+	.ipproto = 253,
+	.hash_report = VIRTIO_NET_HASH_REPORT_IPv4,
+	.hash_value = 0x6e45d952
+};
+
+FIXTURE_VARIANT_ADD(tun_vnet_rss, tcpv4)
+{
+	.eth_p = ETH_P_IP,
+	.ipproto = IPPROTO_TCP,
+	.hash_report = VIRTIO_NET_HASH_REPORT_TCPv4,
+	.hash_value = 0xfb63539a
+};
+
+FIXTURE_VARIANT_ADD(tun_vnet_rss, udpv4)
+{
+	.eth_p = ETH_P_IP,
+	.ipproto = IPPROTO_UDP,
+	.hash_report = VIRTIO_NET_HASH_REPORT_UDPv4,
+	.hash_value = 0xfb63539a
+};
+
+FIXTURE_VARIANT_ADD(tun_vnet_rss, ipv6)
+{
+	.eth_p = ETH_P_IPV6,
+	.ipproto = 253,
+	.hash_report = VIRTIO_NET_HASH_REPORT_IPv6,
+	.hash_value = 0xd6eb560f
+};
+
+FIXTURE_VARIANT_ADD(tun_vnet_rss, tcpv6)
+{
+	.eth_p = ETH_P_IPV6,
+	.ipproto = IPPROTO_TCP,
+	.hash_report = VIRTIO_NET_HASH_REPORT_TCPv6,
+	.hash_value = 0xc2b9f251
+};
+
+FIXTURE_VARIANT_ADD(tun_vnet_rss, udpv6)
+{
+	.eth_p = ETH_P_IPV6,
+	.ipproto = IPPROTO_UDP,
+	.hash_report = VIRTIO_NET_HASH_REPORT_UDPv6,
+	.hash_value = 0xc2b9f251
+};
+
+FIXTURE_SETUP(tun_vnet_rss)
+{
+	static const struct {
+		struct tun_vnet_rss hdr;
+		uint16_t indirection_table[2];
+		uint8_t key[40];
+	} vnet_rss = {
+		.hdr = {
+			.hash_types = VIRTIO_NET_RSS_HASH_TYPE_IPv4 |
+				      VIRTIO_NET_RSS_HASH_TYPE_TCPv4 |
+				      VIRTIO_NET_RSS_HASH_TYPE_UDPv4 |
+				      VIRTIO_NET_RSS_HASH_TYPE_IPv6 |
+				      VIRTIO_NET_RSS_HASH_TYPE_TCPv6 |
+				      VIRTIO_NET_RSS_HASH_TYPE_UDPv6,
+			.indirection_table_mask = 1,
+			.unclassified_queue = 5
+		},
+		.indirection_table = { 3, 4 },
+		.key = {
+			0x6d, 0x5a, 0x56, 0xda, 0x25, 0x5b, 0x0e, 0xc2,
+			0x41, 0x67, 0x25, 0x3d, 0x43, 0xa3, 0x8f, 0xb0,
+			0xd0, 0xca, 0x2b, 0xcb, 0xae, 0x7b, 0x30, 0xb4,
+			0x77, 0xcb, 0x2d, 0xa3, 0x80, 0x30, 0xf2, 0x0c,
+			0x6a, 0x42, 0xb7, 0x3b, 0xbe, 0xac, 0x01, 0xfa
+		}
+	};
+
+	struct {
+		struct virtio_net_hdr_v1_hash vnet_hdr;
+		struct ethhdr ethhdr;
+		struct arphdr arphdr;
+		unsigned char sender_hwaddr[6];
+		uint32_t sender_ipaddr;
+		unsigned char target_hwaddr[6];
+		uint32_t target_ipaddr;
+	} __packed packet = {
+		.ethhdr = {
+			.h_source = TUN_HWADDR_SOURCE,
+			.h_dest = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
+			.h_proto = htons(ETH_P_ARP)
+		},
+		.arphdr = {
+			.ar_hrd = htons(ARPHRD_ETHER),
+			.ar_pro = htons(ETH_P_IP),
+			.ar_hln = ETH_ALEN,
+			.ar_pln = 4,
+			.ar_op = htons(ARPOP_REQUEST)
+		},
+		.sender_hwaddr = TUN_HWADDR_DEST,
+		.sender_ipaddr = TUN_IPADDR_DEST,
+		.target_ipaddr = TUN_IPADDR_DEST
+	};
+
+	char dest_ifname[IFNAMSIZ] = "";
+	int i, local_fd;
+	uint16_t ip_payload_len;
+	uint32_t hash_types;
+	uint32_t ip_sum;
+
+	self->dest_fds[0] = tun_alloc(dest_ifname, IFF_VNET_HDR);
+	ASSERT_LE(0, self->dest_fds[0]) {
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+	}
+
+	i = ioctl(self->dest_fds[0], TUNGETVNETHASHTYPES, &hash_types);
+	if (i == -1 && errno == EINVAL) {
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+		SKIP(return, "TUNGETVNETHASHTYPES not supported");
+	}
+
+	ASSERT_EQ(0, i)
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+
+	if ((hash_types & vnet_rss.hdr.hash_types) != vnet_rss.hdr.hash_types) {
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+		SKIP(return, "Lacks some hash type support");
+	}
+
+	self->dest_ifindex = if_nametoindex(dest_ifname);
+	ASSERT_TRUE(self->dest_ifindex)
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+
+	i = sizeof(struct virtio_net_hdr_v1_hash);
+	ASSERT_EQ(0, ioctl(self->dest_fds[0], TUNSETVNETHDRSZ, &i))
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+
+	i = 1;
+	ASSERT_EQ(0, ioctl(self->dest_fds[0], TUNSETVNETLE, &i))
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+
+	local_fd = socket(AF_LOCAL, SOCK_STREAM, 0);
+	ASSERT_LE(0, local_fd)
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+
+	i = tun_set_flags(local_fd, dest_ifname, IFF_UP);
+	EXPECT_EQ(0, close(local_fd));
+	ASSERT_TRUE(i)
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+
+	ASSERT_EQ(sizeof(packet),
+		  write(self->dest_fds[0], &packet, sizeof(packet)))
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+
+	ASSERT_EQ(0, ioctl(self->dest_fds[0], TUNSETVNETREPORTINGRSS, &vnet_rss))
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+
+	self->source_fd = socket(AF_PACKET, SOCK_DGRAM, 0);
+	ASSERT_LE(0, self->source_fd)
+		EXPECT_EQ(0, close(self->dest_fds[0]));
+
+	for (i = 1; i < ARRAY_SIZE(self->dest_fds); i++) {
+		self->dest_fds[i] = tun_alloc(dest_ifname, IFF_VNET_HDR);
+		ASSERT_LE(0, self->dest_fds[i]) {
+			while (i) {
+				i--;
+				EXPECT_EQ(0, close(self->dest_fds[i]));
+			}
+		}
+	}
+
+	if (variant->eth_p == ETH_P_IP || variant->eth_p == ETH_P_IPV6) {
+		switch (variant->ipproto) {
+		case IPPROTO_TCP:
+			ip_payload_len = sizeof(struct tcphdr);
+			break;
+
+		case IPPROTO_UDP:
+			ip_payload_len = sizeof(struct udphdr);
+			break;
+
+		default:
+			ip_payload_len = 0;
+		}
+
+		switch (variant->eth_p) {
+		case ETH_P_IP:
+			tun_build_iphdr(self->buffer, ip_payload_len, variant->ipproto);
+			self->len = sizeof(struct iphdr);
+			ip_sum = tun_build_ip_pseudo_sum(self->buffer);
+			break;
+
+		case ETH_P_IPV6:
+			tun_build_ipv6hdr(self->buffer, ip_payload_len, variant->ipproto);
+			self->len = sizeof(struct ipv6hdr);
+			ip_sum = tun_build_ipv6_pseudo_sum(self->buffer);
+			break;
+		}
+
+		switch (variant->ipproto) {
+		case IPPROTO_TCP:
+			tun_build_tcphdr(self->buffer + self->len, ip_sum);
+			break;
+
+		case IPPROTO_UDP:
+			tun_build_udphdr(self->buffer + self->len, ip_sum);
+			break;
+		}
+
+		self->len += ip_payload_len;
+	}
+}
+
+FIXTURE_TEARDOWN(tun_vnet_rss)
+{
+	EXPECT_EQ(0, close(self->source_fd));
+
+	for (size_t i = 0; i < ARRAY_SIZE(self->dest_fds); i++)
+		EXPECT_EQ(0, close(self->dest_fds[i]));
+}
+
+TEST_F(tun_vnet_rss, rx)
+{
+	size_t len = sizeof(struct virtio_net_hdr_v1_hash) + ETH_HLEN + self->len;
+	struct {
+		struct virtio_net_hdr_v1_hash vnet_hdr;
+		struct ethhdr ethhdr;
+		char payload[sizeof(self->buffer)];
+	} buffer;
+	struct virtio_net_hdr_v1_hash hdr = {
+		.hdr = { .flags = variant->flags },
+		.hash_value = htole32(variant->hash_value),
+		.hash_report = htole16(variant->hash_report)
+	};
+	int txq = variant->hash_report ? variant->hash_value & 1 : 2;
+	struct sockaddr_ll ll = {
+		.sll_family = AF_PACKET,
+		.sll_addr = TUN_HWADDR_DEST,
+		.sll_halen = ETH_ALEN,
+		.sll_ifindex = self->dest_ifindex,
+		.sll_protocol = htons(variant->eth_p),
+	};
+
+	EXPECT_EQ(self->len,
+		  sendto(self->source_fd, self->buffer, self->len, 0,
+			 (struct sockaddr *)&ll, sizeof(ll)));
+	EXPECT_EQ(len, read(self->dest_fds[txq], &buffer, len));
+	ASSERT_FALSE(memcmp(&buffer, &hdr, sizeof(hdr)));
+	ASSERT_FALSE(memcmp(buffer.payload, self->buffer, self->len));
+}
+
+int main(int argc, char **argv)
+{
+	FILE *file;
+
+	if (unshare(CLONE_NEWNET)) {
+		perror("unshare");
+		return KSFT_FAIL;
+	}
+
+	/* Disable IPv6 to eliminate IPv6 Neighbor Discovery messages. */
+	file = fopen("/proc/sys/net/ipv6/conf/default/disable_ipv6", "w");
+	if (file) {
+		if (fputc('1', file) != '1') {
+			perror("fputc");
+			return KSFT_FAIL;
+		}
+
+		if (fclose(file)) {
+			perror("fclose");
+			return KSFT_FAIL;
+		}
+	} else if (errno != ENOENT) {
+		perror("fopen");
+		return KSFT_FAIL;
+	}
+
+	return test_harness_run(argc, argv);
+}