selftests/net: add csum offload test

Test NIC hardware checksum offload:

- Rx + Tx
- IPv4 + IPv6
- TCP + UDP

Optional features:

- zero checksum 0xFFFF
- checksum disable 0x0000
- transport encap headers
- randomization

See file header for detailed comments.

Expected results differ depending on NIC features:

- CHECKSUM_UNNECESSARY vs CHECKSUM_COMPLETE
- NETIF_F_HW_CSUM (csum_start/csum_off) vs NETIF_F_IP(V6)_CSUM

Signed-off-by: Willem de Bruijn <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/testing/selftests/net/.gitignore

···
 # SPDX-License-Identifier: GPL-2.0-only
 bind_bhash
+csum
 cmsg_sender
 fin_ack_lat
 gro

tools/testing/selftests/net/Makefile

···
 TEST_GEN_PROGS += so_incoming_cpu
 TEST_PROGS += sctp_vrf.sh
 TEST_GEN_FILES += sctp_hello
+TEST_GEN_FILES += csum
 
 TEST_FILES := settings
 

tools/testing/selftests/net/csum.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+/* Test hardware checksum offload: Rx + Tx, IPv4 + IPv6, TCP + UDP.
+ *
+ * The test runs on two machines to exercise the NIC. For this reason it
+ * is not integrated in kselftests.
+ *
+ *     CMD=$((./csum -[46] -[tu] -S $SADDR -D $DADDR -[RT] -r 1 $EXTRA_ARGS))
+ *
+ * Rx:
+ *
+ * The sender sends packets with a known checksum field using PF_INET(6)
+ * SOCK_RAW sockets.
+ *
+ * good packet: $CMD [-t]
+ * bad packet:  $CMD [-t] -E
+ *
+ * The receiver reads UDP packets with a UDP socket. This is not an
+ * option for TCP packets ('-t'). Optionally insert an iptables filter
+ * to avoid these entering the real protocol stack.
+ *
+ * The receiver also reads all packets with a PF_PACKET socket, to
+ * observe whether both good and bad packets arrive on the host. And to
+ * read the optional TP_STATUS_CSUM_VALID bit. This requires setting
+ * option PACKET_AUXDATA, and works only for CHECKSUM_UNNECESSARY.
+ *
+ * Tx:
+ *
+ * The sender needs to build CHECKSUM_PARTIAL packets to exercise tx
+ * checksum offload.
+ *
+ * The sender can sends packets with a UDP socket.
+ *
+ * Optionally crafts a packet that sums up to zero to verify that the
+ * device writes negative zero 0xFFFF in this case to distinguish from
+ * 0x0000 (checksum disabled), as required by RFC 768. Hit this case
+ * by choosing a specific source port.
+ *
+ * good packet: $CMD -U
+ * zero csum:   $CMD -U -Z
+ *
+ * The sender can also build packets with PF_PACKET with PACKET_VNET_HDR,
+ * to cover more protocols. PF_PACKET requires passing src and dst mac
+ * addresses.
+ *
+ * good packet: $CMD -s $smac -d $dmac -p [-t]
+ *
+ * Argument '-z' sends UDP packets with a 0x000 checksum disabled field,
+ * to verify that the NIC passes these packets unmodified.
+ *
+ * Argument '-e' adds a transport mode encapsulation header between
+ * network and transport header. This will fail for devices that parse
+ *  headers. Should work on devices that implement protocol agnostic tx
+ * checksum offload (NETIF_F_HW_CSUM).
+ *
+ * Argument '-r $SEED' optionally randomizes header, payload and length
+ * to increase coverage between packets sent. SEED 1 further chooses a
+ * different seed for each run (and logs this for reproducibility). It
+ * is advised to enable this for extra coverage in continuous testing.
+ */
+
+#define _GNU_SOURCE
+
+#include <arpa/inet.h>
+#include <asm/byteorder.h>
+#include <errno.h>
+#include <error.h>
+#include <linux/filter.h>
+#include <linux/if_packet.h>
+#include <linux/ipv6.h>
+#include <linux/virtio_net.h>
+#include <net/ethernet.h>
+#include <net/if.h>
+#include <netinet/if_ether.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/ip6.h>
+#include <netinet/tcp.h>
+#include <netinet/udp.h>
+#include <poll.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+static bool cfg_bad_csum;
+static int cfg_family = PF_INET6;
+static int cfg_num_pkt = 4;
+static bool cfg_do_rx = true;
+static bool cfg_do_tx = true;
+static bool cfg_encap;
+static char *cfg_ifname = "eth0";
+static char *cfg_mac_dst;
+static char *cfg_mac_src;
+static int cfg_proto = IPPROTO_UDP;
+static int cfg_payload_char = 'a';
+static int cfg_payload_len = 100;
+static uint16_t cfg_port_dst = 34000;
+static uint16_t cfg_port_src = 33000;
+static uint16_t cfg_port_src_encap = 33001;
+static unsigned int cfg_random_seed;
+static int cfg_rcvbuf = 1 << 22;	/* be able to queue large cfg_num_pkt */
+static bool cfg_send_pfpacket;
+static bool cfg_send_udp;
+static int cfg_timeout_ms = 2000;
+static bool cfg_zero_disable; /* skip checksum: set to zero (udp only) */
+static bool cfg_zero_sum;     /* create packet that adds up to zero */
+
+static struct sockaddr_in cfg_daddr4 = {.sin_family = AF_INET};
+static struct sockaddr_in cfg_saddr4 = {.sin_family = AF_INET};
+static struct sockaddr_in6 cfg_daddr6 = {.sin6_family = AF_INET6};
+static struct sockaddr_in6 cfg_saddr6 = {.sin6_family = AF_INET6};
+
+#define ENC_HEADER_LEN	(sizeof(struct udphdr) + sizeof(struct udp_encap_hdr))
+#define MAX_HEADER_LEN	(sizeof(struct ipv6hdr) + ENC_HEADER_LEN + sizeof(struct tcphdr))
+#define MAX_PAYLOAD_LEN 1024
+
+/* Trivial demo encap. Stand-in for transport layer protocols like ESP or PSP */
+struct udp_encap_hdr {
+	uint8_t nexthdr;
+	uint8_t padding[3];
+};
+
+/* Ipaddrs, for pseudo csum. Global var is ugly, pass through funcs was worse */
+static void *iph_addr_p;
+
+static unsigned long gettimeofday_ms(void)
+{
+	struct timeval tv;
+
+	gettimeofday(&tv, NULL);
+	return (tv.tv_sec * 1000UL) + (tv.tv_usec / 1000UL);
+}
+
+static uint32_t checksum_nofold(char *data, size_t len, uint32_t sum)
+{
+	uint16_t *words = (uint16_t *)data;
+	int i;
+
+	for (i = 0; i < len / 2; i++)
+		sum += words[i];
+
+	if (len & 1)
+		sum += ((unsigned char *)data)[len - 1];
+
+	return sum;
+}
+
+static uint16_t checksum_fold(void *data, size_t len, uint32_t sum)
+{
+	sum = checksum_nofold(data, len, sum);
+
+	while (sum > 0xFFFF)
+		sum = (sum & 0xFFFF) + (sum >> 16);
+
+	return ~sum;
+}
+
+static uint16_t checksum(void *th, uint16_t proto, size_t len)
+{
+	uint32_t sum;
+	int alen;
+
+	alen = cfg_family == PF_INET6 ? 32 : 8;
+
+	sum = checksum_nofold(iph_addr_p, alen, 0);
+	sum += htons(proto);
+	sum += htons(len);
+
+	/* With CHECKSUM_PARTIAL kernel expects non-inverted pseudo csum */
+	if (cfg_do_tx && cfg_send_pfpacket)
+		return ~checksum_fold(NULL, 0, sum);
+	else
+		return checksum_fold(th, len, sum);
+}
+
+static void *build_packet_ipv4(void *_iph, uint8_t proto, unsigned int len)
+{
+	struct iphdr *iph = _iph;
+
+	memset(iph, 0, sizeof(*iph));
+
+	iph->version = 4;
+	iph->ihl = 5;
+	iph->ttl = 8;
+	iph->protocol = proto;
+	iph->saddr = cfg_saddr4.sin_addr.s_addr;
+	iph->daddr = cfg_daddr4.sin_addr.s_addr;
+	iph->tot_len = htons(sizeof(*iph) + len);
+	iph->check = checksum_fold(iph, sizeof(*iph), 0);
+
+	iph_addr_p = &iph->saddr;
+
+	return iph + 1;
+}
+
+static void *build_packet_ipv6(void *_ip6h, uint8_t proto, unsigned int len)
+{
+	struct ipv6hdr *ip6h = _ip6h;
+
+	memset(ip6h, 0, sizeof(*ip6h));
+
+	ip6h->version = 6;
+	ip6h->payload_len = htons(len);
+	ip6h->nexthdr = proto;
+	ip6h->hop_limit = 64;
+	ip6h->saddr = cfg_saddr6.sin6_addr;
+	ip6h->daddr = cfg_daddr6.sin6_addr;
+
+	iph_addr_p = &ip6h->saddr;
+
+	return ip6h + 1;
+}
+
+static void *build_packet_udp(void *_uh)
+{
+	struct udphdr *uh = _uh;
+
+	uh->source = htons(cfg_port_src);
+	uh->dest = htons(cfg_port_dst);
+	uh->len = htons(sizeof(*uh) + cfg_payload_len);
+	uh->check = 0;
+
+	/* choose source port so that uh->check adds up to zero */
+	if (cfg_zero_sum) {
+		uh->source = 0;
+		uh->source = checksum(uh, IPPROTO_UDP, sizeof(*uh) + cfg_payload_len);
+
+		fprintf(stderr, "tx: changing sport: %hu -> %hu\n",
+			cfg_port_src, ntohs(uh->source));
+		cfg_port_src = ntohs(uh->source);
+	}
+
+	if (cfg_zero_disable)
+		uh->check = 0;
+	else
+		uh->check = checksum(uh, IPPROTO_UDP, sizeof(*uh) + cfg_payload_len);
+
+	if (cfg_bad_csum)
+		uh->check = ~uh->check;
+
+	fprintf(stderr, "tx: sending checksum: 0x%x\n", uh->check);
+	return uh + 1;
+}
+
+static void *build_packet_tcp(void *_th)
+{
+	struct tcphdr *th = _th;
+
+	th->source = htons(cfg_port_src);
+	th->dest = htons(cfg_port_dst);
+	th->doff = 5;
+	th->check = 0;
+
+	th->check = checksum(th, IPPROTO_TCP, sizeof(*th) + cfg_payload_len);
+
+	if (cfg_bad_csum)
+		th->check = ~th->check;
+
+	fprintf(stderr, "tx: sending checksum: 0x%x\n", th->check);
+	return th + 1;
+}
+
+static char *build_packet_udp_encap(void *_uh)
+{
+	struct udphdr *uh = _uh;
+	struct udp_encap_hdr *eh = _uh + sizeof(*uh);
+
+	/* outer dst == inner dst, to simplify BPF filter
+	 * outer src != inner src, to demultiplex on recv
+	 */
+	uh->dest = htons(cfg_port_dst);
+	uh->source = htons(cfg_port_src_encap);
+	uh->check = 0;
+	uh->len = htons(sizeof(*uh) +
+			sizeof(*eh) +
+			sizeof(struct tcphdr) +
+			cfg_payload_len);
+
+	eh->nexthdr = IPPROTO_TCP;
+
+	return build_packet_tcp(eh + 1);
+}
+
+static char *build_packet(char *buf, int max_len, int *len)
+{
+	uint8_t proto;
+	char *off;
+	int tlen;
+
+	if (cfg_random_seed) {
+		int *buf32 = (void *)buf;
+		int i;
+
+		for (i = 0; i < (max_len / sizeof(int)); i++)
+			buf32[i] = rand();
+	} else {
+		memset(buf, cfg_payload_char, max_len);
+	}
+
+	if (cfg_proto == IPPROTO_UDP)
+		tlen = sizeof(struct udphdr) + cfg_payload_len;
+	else
+		tlen = sizeof(struct tcphdr) + cfg_payload_len;
+
+	if (cfg_encap) {
+		proto = IPPROTO_UDP;
+		tlen += ENC_HEADER_LEN;
+	} else {
+		proto = cfg_proto;
+	}
+
+	if (cfg_family == PF_INET)
+		off = build_packet_ipv4(buf, proto, tlen);
+	else
+		off = build_packet_ipv6(buf, proto, tlen);
+
+	if (cfg_encap)
+		off = build_packet_udp_encap(off);
+	else if (cfg_proto == IPPROTO_UDP)
+		off = build_packet_udp(off);
+	else
+		off = build_packet_tcp(off);
+
+	/* only pass the payload, but still compute headers for cfg_zero_sum */
+	if (cfg_send_udp) {
+		*len = cfg_payload_len;
+		return off;
+	}
+
+	*len = off - buf + cfg_payload_len;
+	return buf;
+}
+
+static int open_inet(int ipproto, int protocol)
+{
+	int fd;
+
+	fd = socket(cfg_family, ipproto, protocol);
+	if (fd == -1)
+		error(1, errno, "socket inet");
+
+	if (cfg_family == PF_INET6) {
+		/* may have been updated by cfg_zero_sum */
+		cfg_saddr6.sin6_port = htons(cfg_port_src);
+
+		if (bind(fd, (void *)&cfg_saddr6, sizeof(cfg_saddr6)))
+			error(1, errno, "bind dgram 6");
+		if (connect(fd, (void *)&cfg_daddr6, sizeof(cfg_daddr6)))
+			error(1, errno, "connect dgram 6");
+	} else {
+		/* may have been updated by cfg_zero_sum */
+		cfg_saddr4.sin_port = htons(cfg_port_src);
+
+		if (bind(fd, (void *)&cfg_saddr4, sizeof(cfg_saddr4)))
+			error(1, errno, "bind dgram 4");
+		if (connect(fd, (void *)&cfg_daddr4, sizeof(cfg_daddr4)))
+			error(1, errno, "connect dgram 4");
+	}
+
+	return fd;
+}
+
+static int open_packet(void)
+{
+	int fd, one = 1;
+
+	fd = socket(PF_PACKET, SOCK_RAW, 0);
+	if (fd == -1)
+		error(1, errno, "socket packet");
+
+	if (setsockopt(fd, SOL_PACKET, PACKET_VNET_HDR, &one, sizeof(one)))
+		error(1, errno, "setsockopt packet_vnet_ndr");
+
+	return fd;
+}
+
+static void send_inet(int fd, const char *buf, int len)
+{
+	int ret;
+
+	ret = write(fd, buf, len);
+	if (ret == -1)
+		error(1, errno, "write");
+	if (ret != len)
+		error(1, 0, "write: %d", ret);
+}
+
+static void eth_str_to_addr(const char *str, unsigned char *eth)
+{
+	if (sscanf(str, "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
+		   &eth[0], &eth[1], &eth[2], &eth[3], &eth[4], &eth[5]) != 6)
+		error(1, 0, "cannot parse mac addr %s", str);
+}
+
+static void send_packet(int fd, const char *buf, int len)
+{
+	struct virtio_net_hdr vh = {0};
+	struct sockaddr_ll addr = {0};
+	struct msghdr msg = {0};
+	struct ethhdr eth;
+	struct iovec iov[3];
+	int ret;
+
+	addr.sll_family = AF_PACKET;
+	addr.sll_halen = ETH_ALEN;
+	addr.sll_ifindex = if_nametoindex(cfg_ifname);
+	if (!addr.sll_ifindex)
+		error(1, errno, "if_nametoindex %s", cfg_ifname);
+
+	vh.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
+	if (cfg_family == PF_INET6) {
+		vh.csum_start = sizeof(struct ethhdr) + sizeof(struct ipv6hdr);
+		addr.sll_protocol = htons(ETH_P_IPV6);
+	} else {
+		vh.csum_start = sizeof(struct ethhdr) + sizeof(struct iphdr);
+		addr.sll_protocol = htons(ETH_P_IP);
+	}
+
+	if (cfg_encap)
+		vh.csum_start += ENC_HEADER_LEN;
+
+	if (cfg_proto == IPPROTO_TCP) {
+		vh.csum_offset = __builtin_offsetof(struct tcphdr, check);
+		vh.hdr_len = vh.csum_start + sizeof(struct tcphdr);
+	} else {
+		vh.csum_offset = __builtin_offsetof(struct udphdr, check);
+		vh.hdr_len = vh.csum_start + sizeof(struct udphdr);
+	}
+
+	eth_str_to_addr(cfg_mac_src, eth.h_source);
+	eth_str_to_addr(cfg_mac_dst, eth.h_dest);
+	eth.h_proto = addr.sll_protocol;
+
+	iov[0].iov_base = &vh;
+	iov[0].iov_len = sizeof(vh);
+
+	iov[1].iov_base = &eth;
+	iov[1].iov_len = sizeof(eth);
+
+	iov[2].iov_base = (void *)buf;
+	iov[2].iov_len = len;
+
+	msg.msg_iov = iov;
+	msg.msg_iovlen = sizeof(iov) / sizeof(iov[0]);
+
+	msg.msg_name = &addr;
+	msg.msg_namelen = sizeof(addr);
+
+	ret = sendmsg(fd, &msg, 0);
+	if (ret == -1)
+		error(1, errno, "sendmsg packet");
+	if (ret != sizeof(vh) + sizeof(eth) + len)
+		error(1, errno, "sendmsg packet: %u", ret);
+}
+
+static int recv_prepare_udp(void)
+{
+	int fd;
+
+	fd = socket(cfg_family, SOCK_DGRAM, 0);
+	if (fd == -1)
+		error(1, errno, "socket r");
+
+	if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF,
+		       &cfg_rcvbuf, sizeof(cfg_rcvbuf)))
+		error(1, errno, "setsockopt SO_RCVBUF r");
+
+	if (cfg_family == PF_INET6) {
+		if (bind(fd, (void *)&cfg_daddr6, sizeof(cfg_daddr6)))
+			error(1, errno, "bind r");
+	} else {
+		if (bind(fd, (void *)&cfg_daddr4, sizeof(cfg_daddr4)))
+			error(1, errno, "bind r");
+	}
+
+	return fd;
+}
+
+/* Filter out all traffic that is not cfg_proto with our destination port.
+ *
+ * Otherwise background noise may cause PF_PACKET receive queue overflow,
+ * dropping the expected packets and failing the test.
+ */
+static void __recv_prepare_packet_filter(int fd, int off_nexthdr, int off_dport)
+{
+	struct sock_filter filter[] = {
+		BPF_STMT(BPF_LD + BPF_B + BPF_ABS, SKF_AD_OFF + SKF_AD_PKTTYPE),
+		BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, PACKET_HOST, 0, 4),
+		BPF_STMT(BPF_LD + BPF_B + BPF_ABS, off_nexthdr),
+		BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, cfg_encap ? IPPROTO_UDP : cfg_proto, 0, 2),
+		BPF_STMT(BPF_LD + BPF_H + BPF_ABS, off_dport),
+		BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, cfg_port_dst, 1, 0),
+		BPF_STMT(BPF_RET + BPF_K, 0),
+		BPF_STMT(BPF_RET + BPF_K, 0xFFFF),
+	};
+	struct sock_fprog prog = {};
+
+	prog.filter = filter;
+	prog.len = sizeof(filter) / sizeof(struct sock_filter);
+	if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &prog, sizeof(prog)))
+		error(1, errno, "setsockopt filter");
+}
+
+static void recv_prepare_packet_filter(int fd)
+{
+	const int off_dport = offsetof(struct tcphdr, dest); /* same for udp */
+
+	if (cfg_family == AF_INET)
+		__recv_prepare_packet_filter(fd, offsetof(struct iphdr, protocol),
+					     sizeof(struct iphdr) + off_dport);
+	else
+		__recv_prepare_packet_filter(fd, offsetof(struct ipv6hdr, nexthdr),
+					     sizeof(struct ipv6hdr) + off_dport);
+}
+
+static void recv_prepare_packet_bind(int fd)
+{
+	struct sockaddr_ll laddr = {0};
+
+	laddr.sll_family = AF_PACKET;
+
+	if (cfg_family == PF_INET)
+		laddr.sll_protocol = htons(ETH_P_IP);
+	else
+		laddr.sll_protocol = htons(ETH_P_IPV6);
+
+	laddr.sll_ifindex = if_nametoindex(cfg_ifname);
+	if (!laddr.sll_ifindex)
+		error(1, 0, "if_nametoindex %s", cfg_ifname);
+
+	if (bind(fd, (void *)&laddr, sizeof(laddr)))
+		error(1, errno, "bind pf_packet");
+}
+
+static int recv_prepare_packet(void)
+{
+	int fd, one = 1;
+
+	fd = socket(PF_PACKET, SOCK_DGRAM, 0);
+	if (fd == -1)
+		error(1, errno, "socket p");
+
+	if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF,
+		       &cfg_rcvbuf, sizeof(cfg_rcvbuf)))
+		error(1, errno, "setsockopt SO_RCVBUF p");
+
+	/* enable auxdata to recv checksum status (valid vs unknown) */
+	if (setsockopt(fd, SOL_PACKET, PACKET_AUXDATA, &one, sizeof(one)))
+		error(1, errno, "setsockopt auxdata");
+
+	/* install filter to restrict packet flow to match */
+	recv_prepare_packet_filter(fd);
+
+	/* bind to address family to start packet flow */
+	recv_prepare_packet_bind(fd);
+
+	return fd;
+}
+
+static int recv_udp(int fd)
+{
+	static char buf[MAX_PAYLOAD_LEN];
+	int ret, count = 0;
+
+	while (1) {
+		ret = recv(fd, buf, sizeof(buf), MSG_DONTWAIT);
+		if (ret == -1 && errno == EAGAIN)
+			break;
+		if (ret == -1)
+			error(1, errno, "recv r");
+
+		fprintf(stderr, "rx: udp: len=%u\n", ret);
+		count++;
+	}
+
+	return count;
+}
+
+static int recv_verify_csum(void *th, int len, uint16_t sport, uint16_t csum_field)
+{
+	uint16_t csum;
+
+	csum = checksum(th, cfg_proto, len);
+
+	fprintf(stderr, "rx: pkt: sport=%hu len=%u csum=0x%hx verify=0x%hx\n",
+		sport, len, csum_field, csum);
+
+	/* csum must be zero unless cfg_bad_csum indicates bad csum */
+	if (csum && !cfg_bad_csum) {
+		fprintf(stderr, "pkt: bad csum\n");
+		return 1;
+	} else if (cfg_bad_csum && !csum) {
+		fprintf(stderr, "pkt: good csum, while bad expected\n");
+		return 1;
+	}
+
+	if (cfg_zero_sum && csum_field != 0xFFFF) {
+		fprintf(stderr, "pkt: zero csum: field should be 0xFFFF, is 0x%hx\n", csum_field);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int recv_verify_packet_tcp(void *th, int len)
+{
+	struct tcphdr *tcph = th;
+
+	if (len < sizeof(*tcph) || tcph->dest != htons(cfg_port_dst))
+		return -1;
+
+	return recv_verify_csum(th, len, ntohs(tcph->source), tcph->check);
+}
+
+static int recv_verify_packet_udp_encap(void *th, int len)
+{
+	struct udp_encap_hdr *eh = th;
+
+	if (len < sizeof(*eh) || eh->nexthdr != IPPROTO_TCP)
+		return -1;
+
+	return recv_verify_packet_tcp(eh + 1, len - sizeof(*eh));
+}
+
+static int recv_verify_packet_udp(void *th, int len)
+{
+	struct udphdr *udph = th;
+
+	if (len < sizeof(*udph))
+		return -1;
+
+	if (udph->dest != htons(cfg_port_dst))
+		return -1;
+
+	if (udph->source == htons(cfg_port_src_encap))
+		return recv_verify_packet_udp_encap(udph + 1,
+						    len - sizeof(*udph));
+
+	return recv_verify_csum(th, len, ntohs(udph->source), udph->check);
+}
+
+static int recv_verify_packet_ipv4(void *nh, int len)
+{
+	struct iphdr *iph = nh;
+	uint16_t proto = cfg_encap ? IPPROTO_UDP : cfg_proto;
+
+	if (len < sizeof(*iph) || iph->protocol != proto)
+		return -1;
+
+	iph_addr_p = &iph->saddr;
+	if (proto == IPPROTO_TCP)
+		return recv_verify_packet_tcp(iph + 1, len - sizeof(*iph));
+	else
+		return recv_verify_packet_udp(iph + 1, len - sizeof(*iph));
+}
+
+static int recv_verify_packet_ipv6(void *nh, int len)
+{
+	struct ipv6hdr *ip6h = nh;
+	uint16_t proto = cfg_encap ? IPPROTO_UDP : cfg_proto;
+
+	if (len < sizeof(*ip6h) || ip6h->nexthdr != proto)
+		return -1;
+
+	iph_addr_p = &ip6h->saddr;
+
+	if (proto == IPPROTO_TCP)
+		return recv_verify_packet_tcp(ip6h + 1, len - sizeof(*ip6h));
+	else
+		return recv_verify_packet_udp(ip6h + 1, len - sizeof(*ip6h));
+}
+
+/* return whether auxdata includes TP_STATUS_CSUM_VALID */
+static bool recv_verify_packet_csum(struct msghdr *msg)
+{
+	struct tpacket_auxdata *aux = NULL;
+	struct cmsghdr *cm;
+
+	if (msg->msg_flags & MSG_CTRUNC)
+		error(1, 0, "cmsg: truncated");
+
+	for (cm = CMSG_FIRSTHDR(msg); cm; cm = CMSG_NXTHDR(msg, cm)) {
+		if (cm->cmsg_level != SOL_PACKET ||
+		    cm->cmsg_type != PACKET_AUXDATA)
+			error(1, 0, "cmsg: level=%d type=%d\n",
+			      cm->cmsg_level, cm->cmsg_type);
+
+		if (cm->cmsg_len != CMSG_LEN(sizeof(struct tpacket_auxdata)))
+			error(1, 0, "cmsg: len=%lu expected=%lu",
+			      cm->cmsg_len, CMSG_LEN(sizeof(struct tpacket_auxdata)));
+
+		aux = (void *)CMSG_DATA(cm);
+	}
+
+	if (!aux)
+		error(1, 0, "cmsg: no auxdata");
+
+	return aux->tp_status & TP_STATUS_CSUM_VALID;
+}
+
+static int recv_packet(int fd)
+{
+	static char _buf[MAX_HEADER_LEN + MAX_PAYLOAD_LEN];
+	unsigned long total = 0, bad_csums = 0, bad_validations = 0;
+	char ctrl[CMSG_SPACE(sizeof(struct tpacket_auxdata))];
+	struct pkt *buf = (void *)_buf;
+	struct msghdr msg = {0};
+	struct iovec iov;
+	int len, ret;
+
+	iov.iov_base = _buf;
+	iov.iov_len = sizeof(_buf);
+
+	msg.msg_iov = &iov;
+	msg.msg_iovlen = 1;
+
+	msg.msg_control = ctrl;
+	msg.msg_controllen = sizeof(ctrl);
+
+	while (1) {
+		msg.msg_flags = 0;
+
+		len = recvmsg(fd, &msg, MSG_DONTWAIT);
+		if (len == -1 && errno == EAGAIN)
+			break;
+		if (len == -1)
+			error(1, errno, "recv p");
+
+		if (cfg_family == PF_INET6)
+			ret = recv_verify_packet_ipv6(buf, len);
+		else
+			ret = recv_verify_packet_ipv4(buf, len);
+
+		if (ret == -1 /* skip: non-matching */)
+			continue;
+
+		total++;
+		if (ret == 1)
+			bad_csums++;
+
+		/* Fail if kernel returns valid for known bad csum.
+		 * Do not fail if kernel does not validate a good csum:
+		 * Absence of validation does not imply invalid.
+		 */
+		if (recv_verify_packet_csum(&msg) && cfg_bad_csum) {
+			fprintf(stderr, "cmsg: expected bad csum, pf_packet returns valid\n");
+			bad_validations++;
+		}
+	}
+
+	if (bad_csums || bad_validations)
+		error(1, 0, "rx: errors at pf_packet: total=%lu bad_csums=%lu bad_valids=%lu\n",
+		      total, bad_csums, bad_validations);
+
+	return total;
+}
+
+static void parse_args(int argc, char *const argv[])
+{
+	const char *daddr = NULL, *saddr = NULL;
+	int c;
+
+	while ((c = getopt(argc, argv, "46d:D:eEi:l:L:n:r:PRs:S:tTuUzZ")) != -1) {
+		switch (c) {
+		case '4':
+			cfg_family = PF_INET;
+			break;
+		case '6':
+			cfg_family = PF_INET6;
+			break;
+		case 'd':
+			cfg_mac_dst = optarg;
+			break;
+		case 'D':
+			daddr = optarg;
+			break;
+		case 'e':
+			cfg_encap = true;
+			break;
+		case 'E':
+			cfg_bad_csum = true;
+			break;
+		case 'i':
+			cfg_ifname = optarg;
+			break;
+		case 'l':
+			cfg_payload_len = strtol(optarg, NULL, 0);
+			break;
+		case 'L':
+			cfg_timeout_ms = strtol(optarg, NULL, 0) * 1000;
+			break;
+		case 'n':
+			cfg_num_pkt = strtol(optarg, NULL, 0);
+			break;
+		case 'r':
+			cfg_random_seed = strtol(optarg, NULL, 0);
+			break;
+		case 'P':
+			cfg_send_pfpacket = true;
+			break;
+		case 'R':
+			/* only Rx: used with two machine tests */
+			cfg_do_tx = false;
+			break;
+		case 's':
+			cfg_mac_src = optarg;
+			break;
+		case 'S':
+			saddr = optarg;
+			break;
+		case 't':
+			cfg_proto = IPPROTO_TCP;
+			break;
+		case 'T':
+			/* only Tx: used with two machine tests */
+			cfg_do_rx = false;
+			break;
+		case 'u':
+			cfg_proto = IPPROTO_UDP;
+			break;
+		case 'U':
+			/* send using real udp socket,
+			 * to exercise tx checksum offload
+			 */
+			cfg_send_udp = true;
+			break;
+		case 'z':
+			cfg_zero_disable = true;
+			break;
+		case 'Z':
+			cfg_zero_sum = true;
+			break;
+		default:
+			error(1, 0, "unknown arg %c", c);
+		}
+	}
+
+	if (!daddr || !saddr)
+		error(1, 0, "Must pass -D <daddr> and -S <saddr>");
+
+	if (cfg_do_tx && cfg_send_pfpacket && (!cfg_mac_src || !cfg_mac_dst))
+		error(1, 0, "Transmit with pf_packet requires mac addresses");
+
+	if (cfg_payload_len > MAX_PAYLOAD_LEN)
+		error(1, 0, "Payload length exceeds max");
+
+	if (cfg_proto != IPPROTO_UDP && (cfg_zero_sum || cfg_zero_disable))
+		error(1, 0, "Only UDP supports zero csum");
+
+	if (cfg_zero_sum && !cfg_send_udp)
+		error(1, 0, "Zero checksum conversion requires -U for tx csum offload");
+	if (cfg_zero_sum && cfg_bad_csum)
+		error(1, 0, "Cannot combine zero checksum conversion and invalid checksum");
+	if (cfg_zero_sum && cfg_random_seed)
+		error(1, 0, "Cannot combine zero checksum conversion with randomization");
+
+	if (cfg_family == PF_INET6) {
+		cfg_saddr6.sin6_port = htons(cfg_port_src);
+		cfg_daddr6.sin6_port = htons(cfg_port_dst);
+
+		if (inet_pton(cfg_family, daddr, &cfg_daddr6.sin6_addr) != 1)
+			error(1, errno, "Cannot parse ipv6 -D");
+		if (inet_pton(cfg_family, saddr, &cfg_saddr6.sin6_addr) != 1)
+			error(1, errno, "Cannot parse ipv6 -S");
+	} else {
+		cfg_saddr4.sin_port = htons(cfg_port_src);
+		cfg_daddr4.sin_port = htons(cfg_port_dst);
+
+		if (inet_pton(cfg_family, daddr, &cfg_daddr4.sin_addr) != 1)
+			error(1, errno, "Cannot parse ipv4 -D");
+		if (inet_pton(cfg_family, saddr, &cfg_saddr4.sin_addr) != 1)
+			error(1, errno, "Cannot parse ipv4 -S");
+	}
+
+	if (cfg_do_tx && cfg_random_seed) {
+		/* special case: time-based seed */
+		if (cfg_random_seed == 1)
+			cfg_random_seed = (unsigned int)gettimeofday_ms();
+		srand(cfg_random_seed);
+		fprintf(stderr, "randomization seed: %u\n", cfg_random_seed);
+	}
+}
+
+static void do_tx(void)
+{
+	static char _buf[MAX_HEADER_LEN + MAX_PAYLOAD_LEN];
+	char *buf;
+	int fd, len, i;
+
+	buf = build_packet(_buf, sizeof(_buf), &len);
+
+	if (cfg_send_pfpacket)
+		fd = open_packet();
+	else if (cfg_send_udp)
+		fd = open_inet(SOCK_DGRAM, 0);
+	else
+		fd = open_inet(SOCK_RAW, IPPROTO_RAW);
+
+	for (i = 0; i < cfg_num_pkt; i++) {
+		if (cfg_send_pfpacket)
+			send_packet(fd, buf, len);
+		else
+			send_inet(fd, buf, len);
+
+		/* randomize each packet individually to increase coverage */
+		if (cfg_random_seed) {
+			cfg_payload_len = rand() % MAX_PAYLOAD_LEN;
+			buf = build_packet(_buf, sizeof(_buf), &len);
+		}
+	}
+
+	if (close(fd))
+		error(1, errno, "close tx");
+}
+
+static void do_rx(int fdp, int fdr)
+{
+	unsigned long count_udp = 0, count_pkt = 0;
+	long tleft, tstop;
+	struct pollfd pfd;
+
+	tstop = gettimeofday_ms() + cfg_timeout_ms;
+	tleft = cfg_timeout_ms;
+
+	do {
+		pfd.events = POLLIN;
+		pfd.fd = fdp;
+		if (poll(&pfd, 1, tleft) == -1)
+			error(1, errno, "poll");
+
+		if (pfd.revents & POLLIN)
+			count_pkt += recv_packet(fdp);
+
+		if (cfg_proto == IPPROTO_UDP)
+			count_udp += recv_udp(fdr);
+
+		tleft = tstop - gettimeofday_ms();
+	} while (tleft > 0);
+
+	if (close(fdr))
+		error(1, errno, "close r");
+	if (close(fdp))
+		error(1, errno, "close p");
+
+	if (count_pkt < cfg_num_pkt)
+		error(1, 0, "rx: missing packets at pf_packet: %lu < %u",
+		      count_pkt, cfg_num_pkt);
+
+	if (cfg_proto == IPPROTO_UDP) {
+		if (cfg_bad_csum && count_udp)
+			error(1, 0, "rx: unexpected packets at udp");
+		if (!cfg_bad_csum && !count_udp)
+			error(1, 0, "rx: missing packets at udp");
+	}
+}
+
+int main(int argc, char *const argv[])
+{
+	int fdp = -1, fdr = -1;		/* -1 to silence -Wmaybe-uninitialized */
+
+	parse_args(argc, argv);
+
+	/* open receive sockets before transmitting */
+	if (cfg_do_rx) {
+		fdp = recv_prepare_packet();
+		fdr = recv_prepare_udp();
+	}
+
+	if (cfg_do_tx)
+		do_tx();
+
+	if (cfg_do_rx)
+		do_rx(fdp, fdr);
+
+	fprintf(stderr, "OK\n");
+	return 0;
+}