eppf map机制

/* eBPF example program:
 * - creates arraymap in kernel with key 4 bytes and value 8 bytes
 *
 * - loads eBPF program:
 *   r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)];
 *   *(u32*)(fp - 4) = r0;
 *   // assuming packet is IPv4, lookup ip->proto in a map
 *   value = bpf_map_lookup_elem(map_fd, fp - 4);
 *   if (value)
 *        (*(u64*)value) += 1;
 *
 * - attaches this program to loopback interface "lo" raw socket
 *
 * - every second user space reads map[tcp], map[udp], map[icmp] to see
 *   how many packets of given protocol were seen on "lo"
 */
#include <stdio.h>
#include <unistd.h>
#include <assert.h>
#include <linux/bpf.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <stddef.h>
#include <bpf/bpf.h>
#include "bpf_insn.h"
#include "sock_example.h"

char bpf_log_buf[BPF_LOG_BUF_SIZE];

static int test_sock(void)
{
    int sock = -1, map_fd, prog_fd, i, key;
    long long value = 0, tcp_cnt, udp_cnt, icmp_cnt;

    map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(key), sizeof(value),
                256, 0);
    if (map_fd < 0) {
        printf("failed to create map '%s'
", strerror(errno));
        goto cleanup;
    }

    struct bpf_insn prog[] = {
        BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
        BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol) /* R0 = ip->proto */),
        BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
        BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
        BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
        BPF_LD_MAP_FD(BPF_REG_1, map_fd),
        BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
        BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
        BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
        BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
        BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */
        BPF_EXIT_INSN(),
    };
    size_t insns_cnt = sizeof(prog) / sizeof(struct bpf_insn);

    prog_fd = bpf_load_program(BPF_PROG_TYPE_SOCKET_FILTER, prog, insns_cnt,
                   "GPL", 0, bpf_log_buf, BPF_LOG_BUF_SIZE);
    if (prog_fd < 0) {
        printf("failed to load prog '%s'
", strerror(errno));
        goto cleanup;
    }

    sock = open_raw_sock("lo");

    if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd,
               sizeof(prog_fd)) < 0) {
        printf("setsockopt %s
", strerror(errno));
        goto cleanup;
    }

    for (i = 0; i < 10; i++) {
        key = IPPROTO_TCP;
        assert(bpf_map_lookup_elem(map_fd, &key, &tcp_cnt) == 0);

        key = IPPROTO_UDP;
        assert(bpf_map_lookup_elem(map_fd, &key, &udp_cnt) == 0);

        key = IPPROTO_ICMP;
        assert(bpf_map_lookup_elem(map_fd, &key, &icmp_cnt) == 0);

        printf("TCP %lld UDP %lld ICMP %lld packets
",
               tcp_cnt, udp_cnt, icmp_cnt);
        sleep(1);
    }

cleanup:
    /* maps, programs, raw sockets will auto cleanup on process exit */
    return 0;
}

int main(void)
{
    FILE *f;

    f = popen("ping -c5 localhost", "r");
    (void)f;

    return test_sock();
}

 有如下两种方式加载map

1、BPF_LD_MAP_FD加载map

 /* pseudo BPF_LD_IMM64 insn used to refer to process-local map_fd */
#define BPF_LD_MAP_FD(DST, MAP_FD)
BPF_LD_IMM64_RAW(DST, BPF_PSEUDO_MAP_FD, MAP_FD)

#define BPF_LD_IMM64_RAW(DST, SRC, IMM)
((struct bpf_insn) {
.code = BPF_LD | BPF_DW | BPF_IMM,
.dst_reg = DST,
.src_reg = SRC,
.off = 0,
.imm = (__u32) (IMM) }),
((struct bpf_insn) {
.code = 0, /* zero is reserved opcode */
.dst_reg = 0,
.src_reg = 0,
.off = 0,
.imm = ((__u64) (IMM)) >> 32 })

#ifndef BPF_PSEUDO_MAP_FD
# define BPF_PSEUDO_MAP_FD 1
#endif

bpf_prog_load -->  bpf_check-->replace_map_fd_with_map_ptr

2、replace_map_fd_with_map_ptr 加载map
       struct bpf_insn *insn = env->prog->insnsi;
　　map = __bpf_map_get(f); // from file private_data
　　insn[0].imm = (u32) (unsigned long) map;
　　insn[1].imm = ((u64) (unsigned long) map) >> 32;

/* SPDX-License-Identifier: GPL-2.0 */
#include <stdlib.h>
#include <stdio.h>
#include <linux/unistd.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <linux/if_ether.h>
#include <net/if.h>
#include <linux/if_packet.h>
#include <arpa/inet.h>

static inline int open_raw_sock(const char *name)
{
    struct sockaddr_ll sll;
    int sock;

    sock = socket(PF_PACKET, SOCK_RAW | SOCK_NONBLOCK | SOCK_CLOEXEC, htons(ETH_P_ALL));
    if (sock < 0) {
        printf("cannot create raw socket
");
        return -1;
    }

    memset(&sll, 0, sizeof(sll));
    sll.sll_family = AF_PACKET;
    sll.sll_ifindex = if_nametoindex(name);
    sll.sll_protocol = htons(ETH_P_ALL);
    if (bind(sock, (struct sockaddr *)&sll, sizeof(sll)) < 0) {
        printf("bind to %s: %s
", name, strerror(errno));
        close(sock);
        return -1;
    }

    return sock;
}

 

另外打开两个终端分别执行ping 和telnet操作