mirror of
https://github.com/xdp-project/bpf-examples.git
synced 2024-05-06 15:54:53 +00:00
f2a13d942f
Encode this statically via C/BPF-code switch statement, and have global counter cycles through these. Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
132 lines
2.8 KiB
C
132 lines
2.8 KiB
C
#include <linux/bpf.h>
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#include <linux/in6.h>
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#include <bpf/bpf_helpers.h>
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#include <xdp/parsing_helpers.h>
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#include "encap.h"
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/* Cycle through different MTU packet sizes, encoded in BPF-code via switch
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* statement. MTU is defined as L3 size (usually 1500 for Ethernet), but
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* remember TC (and XDP) operate at L2 (adjusted later)
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*/
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static __always_inline __u32 get_pkt_size_l3(__u64 cnt)
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{
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switch (cnt) {
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case 0:
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return 1024;
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case 1:
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return 1500;
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case 2:
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return 1504;
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case 3:
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return 1508;
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case 4:
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return 1600;
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case 5:
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return 4096 + 128;
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case 6:
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return 3520;
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case 7:
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return 3528;
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case 8:
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return 4096 - 14;
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case 9:
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return 4096;
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case 10:
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return 8192;
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case 11:
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return 16000;
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default:
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return 1500;
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}
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}
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#define CNT_MAX 12
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/* The tc tool (iproute2) use another ELF map layout than libbpf, see
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* struct bpf_elf_map from iproute2, but bpf_map_def from libbpf have
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* same binary layout until "flags" so use that.
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*/
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struct bpf_map_def SEC("maps") cnt_map = {
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.type = BPF_MAP_TYPE_ARRAY,
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.key_size = sizeof(__u32),
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.value_size = sizeof(__u64),
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.max_entries = 1,
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.map_flags = 0,
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};
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/* LLVM maps __sync_fetch_and_add() as a built-in function to the BPF atomic add
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* instruction (that is BPF_STX | BPF_XADD | BPF_W for word sizes)
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*/
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#ifndef lock_xadd
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#define lock_xadd(ptr, val) ((void) __sync_fetch_and_add(ptr, val))
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#endif
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#define ENCAP_TYPE BPF_F_ADJ_ROOM_ENCAP_L3_IPV4
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SEC("classifier") int tc_inc_pkt_sz(struct __sk_buff *skb)
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{
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volatile void *data, *data_end;
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int ret = BPF_DROP;
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struct ethhdr *eth;
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struct iphdr *iph;
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int extra_len;
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int len;
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int key = 0;
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__u64 *cnt;
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cnt = bpf_map_lookup_elem(&cnt_map, &key);
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if (!cnt)
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goto out;
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/* Desired packet size at L2 */
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int pkt_size_l2 = get_pkt_size_l3(*cnt) + sizeof(*eth) ;
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data = (void *)(long)skb->data;
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data_end = (void *)(long)skb->data_end;
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eth = (struct ethhdr *)data;
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if (data + sizeof(*eth) > data_end)
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return BPF_DROP;
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/* Keep ARP resolution working */
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if (eth->h_proto == bpf_htons(ETH_P_ARP)) {
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ret = BPF_OK;
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goto out;
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}
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len = (data_end - data);
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extra_len = pkt_size_l2 - len;
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// extra_len= sizeof(*iph); /* Adj that does correct IPIP encap */
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/* Wrapping global counter */
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lock_xadd(cnt, 1);
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if (*cnt == CNT_MAX)
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*cnt = 0;
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if (bpf_skb_adjust_room(skb, extra_len, BPF_ADJ_ROOM_MAC, ENCAP_TYPE)) {
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/* If adjust fails, then skip this packet length adjustment */
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ret = BPF_OK;
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goto out;
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}
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/* Most re-load after bpf_skb_adjust_room() */
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data = (void *)(long)skb->data;
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data_end = (void *)(long)skb->data_end;
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/* Add IP-header with IPIP */
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encap_ipv4_ipip(data, data_end);
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eth = (void *)data;
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iph = (void *)(eth +1);
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if (iph +1 > data_end)
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goto out;
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eth->h_proto = bpf_htons(ETH_P_IP);
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ret = BPF_OK;
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out:
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return ret;
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}
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char _license[] SEC("license") = "GPL";
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