doc: packet: add minimal TPACKET_V3 example code

Lost in space for a long time, but it finally came back to us from
some ancient code tombs. This patch adds a minimal runnable example
of Linux' packet mmap(2) from Chetan Loke's TPACKET_V3. Special
thanks to David S. Miller, and also Eric Leblond and Victor Julien!

Cc: Eric Leblond <eric@regit.org>
Cc: Victor Julien <victor@inliniac.net>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/packet_mmap.txt

@@ -684,6 +684,333 @@ int main(int argc, char **argp)
 	return 0;
 }
 
+-------------------------------------------------------------------------------
++ AF_PACKET TPACKET_V3 example
+-------------------------------------------------------------------------------
+
+AF_PACKET's TPACKET_V3 ring buffer can be configured to use non-static frame
+sizes by doing it's own memory management. It is based on blocks where polling
+works on a per block basis instead of per ring as in TPACKET_V2 and predecessor.
+
+It is said that TPACKET_V3 brings the following benefits:
+ *) ~15 - 20% reduction in CPU-usage
+ *) ~20% increase in packet capture rate
+ *) ~2x increase in packet density
+ *) Port aggregation analysis
+ *) Non static frame size to capture entire packet payload
+
+So it seems to be a good candidate to be used with packet fanout.
+
+Minimal example code by Daniel Borkmann based on Chetan Loke's lolpcap (compile
+it with gcc -Wall -O2 blob.c, and try things like "./a.out eth0", etc.):
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <assert.h>
+#include <net/if.h>
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <poll.h>
+#include <unistd.h>
+#include <signal.h>
+#include <inttypes.h>
+#include <sys/socket.h>
+#include <sys/mman.h>
+#include <linux/if_packet.h>
+#include <linux/if_ether.h>
+#include <linux/ip.h>
+
+#define BLOCK_SIZE		(1 << 22)
+#define FRAME_SIZE		2048
+
+#define NUM_BLOCKS		64
+#define NUM_FRAMES		((BLOCK_SIZE * NUM_BLOCKS) / FRAME_SIZE)
+
+#define BLOCK_RETIRE_TOV_IN_MS	64
+#define BLOCK_PRIV_AREA_SZ	13
+
+#define ALIGN_8(x)		(((x) + 8 - 1) & ~(8 - 1))
+
+#define BLOCK_STATUS(x)		((x)->h1.block_status)
+#define BLOCK_NUM_PKTS(x)	((x)->h1.num_pkts)
+#define BLOCK_O2FP(x)		((x)->h1.offset_to_first_pkt)
+#define BLOCK_LEN(x)		((x)->h1.blk_len)
+#define BLOCK_SNUM(x)		((x)->h1.seq_num)
+#define BLOCK_O2PRIV(x)		((x)->offset_to_priv)
+#define BLOCK_PRIV(x)		((void *) ((uint8_t *) (x) + BLOCK_O2PRIV(x)))
+#define BLOCK_HDR_LEN		(ALIGN_8(sizeof(struct block_desc)))
+#define BLOCK_PLUS_PRIV(sz_pri)	(BLOCK_HDR_LEN + ALIGN_8((sz_pri)))
+
+#ifndef likely
+# define likely(x)		__builtin_expect(!!(x), 1)
+#endif
+#ifndef unlikely
+# define unlikely(x)		__builtin_expect(!!(x), 0)
+#endif
+
+struct block_desc {
+	uint32_t version;
+	uint32_t offset_to_priv;
+	struct tpacket_hdr_v1 h1;
+};
+
+struct ring {
+	struct iovec *rd;
+	uint8_t *map;
+	struct tpacket_req3 req;
+};
+
+static unsigned long packets_total = 0, bytes_total = 0;
+static sig_atomic_t sigint = 0;
+
+void sighandler(int num)
+{
+	sigint = 1;
+}
+
+static int setup_socket(struct ring *ring, char *netdev)
+{
+	int err, i, fd, v = TPACKET_V3;
+	struct sockaddr_ll ll;
+
+	fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
+	if (fd < 0) {
+		perror("socket");
+		exit(1);
+	}
+
+	err = setsockopt(fd, SOL_PACKET, PACKET_VERSION, &v, sizeof(v));
+	if (err < 0) {
+		perror("setsockopt");
+		exit(1);
+	}
+
+	memset(&ring->req, 0, sizeof(ring->req));
+	ring->req.tp_block_size = BLOCK_SIZE;
+	ring->req.tp_frame_size = FRAME_SIZE;
+	ring->req.tp_block_nr = NUM_BLOCKS;
+	ring->req.tp_frame_nr = NUM_FRAMES;
+	ring->req.tp_retire_blk_tov = BLOCK_RETIRE_TOV_IN_MS;
+	ring->req.tp_sizeof_priv = BLOCK_PRIV_AREA_SZ;
+	ring->req.tp_feature_req_word |= TP_FT_REQ_FILL_RXHASH;
+
+	err = setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &ring->req,
+			 sizeof(ring->req));
+	if (err < 0) {
+		perror("setsockopt");
+		exit(1);
+	}
+
+	ring->map = mmap(NULL, ring->req.tp_block_size * ring->req.tp_block_nr,
+			 PROT_READ | PROT_WRITE, MAP_SHARED | MAP_LOCKED,
+			 fd, 0);
+	if (ring->map == MAP_FAILED) {
+		perror("mmap");
+		exit(1);
+	}
+
+	ring->rd = malloc(ring->req.tp_block_nr * sizeof(*ring->rd));
+	assert(ring->rd);
+	for (i = 0; i < ring->req.tp_block_nr; ++i) {
+		ring->rd[i].iov_base = ring->map + (i * ring->req.tp_block_size);
+		ring->rd[i].iov_len = ring->req.tp_block_size;
+	}
+
+	memset(&ll, 0, sizeof(ll));
+	ll.sll_family = PF_PACKET;
+	ll.sll_protocol = htons(ETH_P_ALL);
+	ll.sll_ifindex = if_nametoindex(netdev);
+	ll.sll_hatype = 0;
+	ll.sll_pkttype = 0;
+	ll.sll_halen = 0;
+
+	err = bind(fd, (struct sockaddr *) &ll, sizeof(ll));
+	if (err < 0) {
+		perror("bind");
+		exit(1);
+	}
+
+	return fd;
+}
+
+#ifdef __checked
+static uint64_t prev_block_seq_num = 0;
+
+void assert_block_seq_num(struct block_desc *pbd)
+{
+	if (unlikely(prev_block_seq_num + 1 != BLOCK_SNUM(pbd))) {
+		printf("prev_block_seq_num:%"PRIu64", expected seq:%"PRIu64" != "
+		       "actual seq:%"PRIu64"\n", prev_block_seq_num,
+		       prev_block_seq_num + 1, (uint64_t) BLOCK_SNUM(pbd));
+		exit(1);
+	}
+
+	prev_block_seq_num = BLOCK_SNUM(pbd);
+}
+
+static void assert_block_len(struct block_desc *pbd, uint32_t bytes, int block_num)
+{
+	if (BLOCK_NUM_PKTS(pbd)) {
+		if (unlikely(bytes != BLOCK_LEN(pbd))) {
+			printf("block:%u with %upackets, expected len:%u != actual len:%u\n",
+			       block_num, BLOCK_NUM_PKTS(pbd), bytes, BLOCK_LEN(pbd));
+			exit(1);
+		}
+	} else {
+		if (unlikely(BLOCK_LEN(pbd) != BLOCK_PLUS_PRIV(BLOCK_PRIV_AREA_SZ))) {
+			printf("block:%u, expected len:%lu != actual len:%u\n",
+			       block_num, BLOCK_HDR_LEN, BLOCK_LEN(pbd));
+			exit(1);
+		}
+	}
+}
+
+static void assert_block_header(struct block_desc *pbd, const int block_num)
+{
+	uint32_t block_status = BLOCK_STATUS(pbd);
+
+	if (unlikely((block_status & TP_STATUS_USER) == 0)) {
+		printf("block:%u, not in TP_STATUS_USER\n", block_num);
+		exit(1);
+	}
+
+	assert_block_seq_num(pbd);
+}
+#else
+static inline void assert_block_header(struct block_desc *pbd, const int block_num)
+{
+}
+static void assert_block_len(struct block_desc *pbd, uint32_t bytes, int block_num)
+{
+}
+#endif
+
+static void display(struct tpacket3_hdr *ppd)
+{
+	struct ethhdr *eth = (struct ethhdr *) ((uint8_t *) ppd + ppd->tp_mac);
+	struct iphdr *ip = (struct iphdr *) ((uint8_t *) eth + ETH_HLEN);
+
+	if (eth->h_proto == htons(ETH_P_IP)) {
+		struct sockaddr_in ss, sd;
+		char sbuff[NI_MAXHOST], dbuff[NI_MAXHOST];
+
+		memset(&ss, 0, sizeof(ss));
+		ss.sin_family = PF_INET;
+		ss.sin_addr.s_addr = ip->saddr;
+		getnameinfo((struct sockaddr *) &ss, sizeof(ss),
+			    sbuff, sizeof(sbuff), NULL, 0, NI_NUMERICHOST);
+
+		memset(&sd, 0, sizeof(sd));
+		sd.sin_family = PF_INET;
+		sd.sin_addr.s_addr = ip->daddr;
+		getnameinfo((struct sockaddr *) &sd, sizeof(sd),
+			    dbuff, sizeof(dbuff), NULL, 0, NI_NUMERICHOST);
+
+		printf("%s -> %s, ", sbuff, dbuff);
+	}
+
+	printf("rxhash: 0x%x\n", ppd->hv1.tp_rxhash);
+}
+
+static void walk_block(struct block_desc *pbd, const int block_num)
+{
+	int num_pkts = BLOCK_NUM_PKTS(pbd), i;
+	unsigned long bytes = 0;
+	unsigned long bytes_with_padding = BLOCK_PLUS_PRIV(BLOCK_PRIV_AREA_SZ);
+	struct tpacket3_hdr *ppd;
+
+	assert_block_header(pbd, block_num);
+
+	ppd = (struct tpacket3_hdr *) ((uint8_t *) pbd + BLOCK_O2FP(pbd));
+	for (i = 0; i < num_pkts; ++i) {
+		bytes += ppd->tp_snaplen;
+		if (ppd->tp_next_offset)
+			bytes_with_padding += ppd->tp_next_offset;
+		else
+			bytes_with_padding += ALIGN_8(ppd->tp_snaplen + ppd->tp_mac);
+
+		display(ppd);
+
+		ppd = (struct tpacket3_hdr *) ((uint8_t *) ppd + ppd->tp_next_offset);
+		__sync_synchronize();
+	}
+
+	assert_block_len(pbd, bytes_with_padding, block_num);
+
+	packets_total += num_pkts;
+	bytes_total += bytes;
+}
+
+void flush_block(struct block_desc *pbd)
+{
+	BLOCK_STATUS(pbd) = TP_STATUS_KERNEL;
+	__sync_synchronize();
+}
+
+static void teardown_socket(struct ring *ring, int fd)
+{
+	munmap(ring->map, ring->req.tp_block_size * ring->req.tp_block_nr);
+	free(ring->rd);
+	close(fd);
+}
+
+int main(int argc, char **argp)
+{
+	int fd, err;
+	socklen_t len;
+	struct ring ring;
+	struct pollfd pfd;
+	unsigned int block_num = 0;
+	struct block_desc *pbd;
+	struct tpacket_stats_v3 stats;
+
+	if (argc != 2) {
+		fprintf(stderr, "Usage: %s INTERFACE\n", argp[0]);
+		return EXIT_FAILURE;
+	}
+
+	signal(SIGINT, sighandler);
+
+	memset(&ring, 0, sizeof(ring));
+	fd = setup_socket(&ring, argp[argc - 1]);
+	assert(fd > 0);
+
+	memset(&pfd, 0, sizeof(pfd));
+	pfd.fd = fd;
+	pfd.events = POLLIN | POLLERR;
+	pfd.revents = 0;
+
+	while (likely(!sigint)) {
+		pbd = (struct block_desc *) ring.rd[block_num].iov_base;
+retry_block:
+		if ((BLOCK_STATUS(pbd) & TP_STATUS_USER) == 0) {
+			poll(&pfd, 1, -1);
+			goto retry_block;
+		}
+
+		walk_block(pbd, block_num);
+		flush_block(pbd);
+		block_num = (block_num + 1) % NUM_BLOCKS;
+	}
+
+	len = sizeof(stats);
+	err = getsockopt(fd, SOL_PACKET, PACKET_STATISTICS, &stats, &len);
+	if (err < 0) {
+		perror("getsockopt");
+		exit(1);
+	}
+
+	fflush(stdout);
+	printf("\nReceived %u packets, %lu bytes, %u dropped, freeze_q_cnt: %u\n",
+	       stats.tp_packets, bytes_total, stats.tp_drops,
+	       stats.tp_freeze_q_cnt);
+
+	teardown_socket(&ring, fd);
+	return 0;
+}
+
 -------------------------------------------------------------------------------
 + PACKET_TIMESTAMP
 -------------------------------------------------------------------------------