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>

1 files changed, 327 insertions, 0 deletions

diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt
index 94444b152fbc..65efb85e49de 100644
--- a/Documentation/networking/packet_mmap.txt
+++ b/Documentation/networking/packet_mmap.txt
@@ -685,6 +685,333 @@ int main(int argc, char **argp)
 }
 
 -------------------------------------------------------------------------------
++ 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
 -------------------------------------------------------------------------------