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Linux/samples/bpf/sock_example.c

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  1 /* eBPF example program:
  2  * - creates arraymap in kernel with key 4 bytes and value 8 bytes
  3  *
  4  * - loads eBPF program:
  5  *   r0 = skb->data[ETH_HLEN + offsetof(struct iphdr, protocol)];
  6  *   *(u32*)(fp - 4) = r0;
  7  *   // assuming packet is IPv4, lookup ip->proto in a map
  8  *   value = bpf_map_lookup_elem(map_fd, fp - 4);
  9  *   if (value)
 10  *        (*(u64*)value) += 1;
 11  *
 12  * - attaches this program to eth0 raw socket
 13  *
 14  * - every second user space reads map[tcp], map[udp], map[icmp] to see
 15  *   how many packets of given protocol were seen on eth0
 16  */
 17 #include <stdio.h>
 18 #include <unistd.h>
 19 #include <assert.h>
 20 #include <linux/bpf.h>
 21 #include <string.h>
 22 #include <stdlib.h>
 23 #include <errno.h>
 24 #include <sys/socket.h>
 25 #include <arpa/inet.h>
 26 #include <linux/if_ether.h>
 27 #include <linux/ip.h>
 28 #include <stddef.h>
 29 #include "libbpf.h"
 30 
 31 static int test_sock(void)
 32 {
 33         int sock = -1, map_fd, prog_fd, i, key;
 34         long long value = 0, tcp_cnt, udp_cnt, icmp_cnt;
 35 
 36         map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(key), sizeof(value),
 37                                 256);
 38         if (map_fd < 0) {
 39                 printf("failed to create map '%s'\n", strerror(errno));
 40                 goto cleanup;
 41         }
 42 
 43         struct bpf_insn prog[] = {
 44                 BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
 45                 BPF_LD_ABS(BPF_B, ETH_HLEN + offsetof(struct iphdr, protocol) /* R0 = ip->proto */),
 46                 BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4), /* *(u32 *)(fp - 4) = r0 */
 47                 BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
 48                 BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = fp - 4 */
 49                 BPF_LD_MAP_FD(BPF_REG_1, map_fd),
 50                 BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
 51                 BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
 52                 BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
 53                 BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
 54                 BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */
 55                 BPF_EXIT_INSN(),
 56         };
 57 
 58         prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog, sizeof(prog),
 59                                 "GPL");
 60         if (prog_fd < 0) {
 61                 printf("failed to load prog '%s'\n", strerror(errno));
 62                 goto cleanup;
 63         }
 64 
 65         sock = open_raw_sock("lo");
 66 
 67         if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd,
 68                        sizeof(prog_fd)) < 0) {
 69                 printf("setsockopt %s\n", strerror(errno));
 70                 goto cleanup;
 71         }
 72 
 73         for (i = 0; i < 10; i++) {
 74                 key = IPPROTO_TCP;
 75                 assert(bpf_lookup_elem(map_fd, &key, &tcp_cnt) == 0);
 76 
 77                 key = IPPROTO_UDP;
 78                 assert(bpf_lookup_elem(map_fd, &key, &udp_cnt) == 0);
 79 
 80                 key = IPPROTO_ICMP;
 81                 assert(bpf_lookup_elem(map_fd, &key, &icmp_cnt) == 0);
 82 
 83                 printf("TCP %lld UDP %lld ICMP %lld packets\n",
 84                        tcp_cnt, udp_cnt, icmp_cnt);
 85                 sleep(1);
 86         }
 87 
 88 cleanup:
 89         /* maps, programs, raw sockets will auto cleanup on process exit */
 90         return 0;
 91 }
 92 
 93 int main(void)
 94 {
 95         FILE *f;
 96 
 97         f = popen("ping -c5 localhost", "r");
 98         (void)f;
 99 
100         return test_sock();
101 }
102 

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