c - AF_XDP : `BPF_MAP_TYPE_XSKMAP` only has entries with `Operation not supported`

Question

这是我所有的 XDP/BPF 内核代码:

struct bpf_map_def SEC("maps") xsks_map = {
    .type = BPF_MAP_TYPE_XSKMAP,
    .key_size = sizeof(int),
    .value_size = sizeof(int),
    .max_entries = 64,  /* Assume netdev has no more than 64 queues */
};

struct bpf_map_def SEC("maps") rx_queue_pckt_counter_map = {
    .type = BPF_MAP_TYPE_ARRAY,
    .key_size = sizeof(int),
    .value_size = sizeof(unsigned long),
    .max_entries = 48,
};

SEC("xdp_sock")
int xdp_sock_prog(struct xdp_md *ctx) {

    int index = ctx->rx_queue_index;

    void *data_end = (void *)(long)ctx->data_end;
    void *data = (void *)(long)ctx->data;

    void *pos = data;
    struct ethhdr *eth = (struct ethhdr*)(pos);

    if(eth + sizeof(struct ethhdr) <= data_end) {

        if(bpf_ntohs(eth->h_proto) == ETH_P_IP) {

            struct iphdr *iph = (struct iphdr*)(pos + sizeof(struct ethhdr));

            if(iph + sizeof(struct iphdr) <= data_end) {

                if(iph->protocol == IPPROTO_UDP) {

                    const __u16 iph_sz_in_bytes = iph->ihl * 4;

                    if(iph + iph_sz_in_bytes <= data_end) {
                        struct udphdr *udh = (struct udphdr*)(pos + sizeof(struct ethhdr) + iph_sz_in_bytes);

                        if(udh + sizeof(struct udphdr) <= data_end) {

                            void *rec = bpf_map_lookup_elem(&rx_queue_pckt_counter_map, &index);
                            if(rec) {
                                long *pckt_counter_val = (long*)(rec);
                                *pckt_counter_val += 1;
                            } else {
                                return XDP_PASS;
                            }

                            if (bpf_map_lookup_elem(&xsks_map, &index)) {

                                const int ret_val = bpf_redirect_map(&xsks_map, index, 0);
                                bpf_printk("RET-VAL: %d\n", ret_val);
                                return ret_val;
                            }
                        }
                    }
                }
            }
        }
    }

    return XDP_PASS;
}

char _license[] SEC("license") = "GPL";

我正在尝试过滤所有 IP-UDP 数据包并将它们发送到用户空间。我还计算了每个 RX-Queue 到达的数据包数量(由 ctx->rx_queue_index 表示)。

我的程序编译得很好，但无论出于何种原因，我的用户空间程序中都没有收到任何数据包。我已经在我的另一篇文章中谈到了这个: AF_XDP: No packets from multicast although steered on RX-Queue 0

我执行了 sudo ethtool -N eth20 flow-type udp4 action 0事先将所有数据包引导到 RX-Queue 0 .

我可以通过以下方式查看当前事件的所有 bpf map

$ sudo bpftool map list       
32: lpm_trie  flags 0x1
        key 8B  value 8B  max_entries 1  memlock 4096B
33: lpm_trie  flags 0x1
        key 20B  value 8B  max_entries 1  memlock 4096B
34: lpm_trie  flags 0x1
        key 8B  value 8B  max_entries 1  memlock 4096B
35: lpm_trie  flags 0x1
        key 20B  value 8B  max_entries 1  memlock 4096B
36: lpm_trie  flags 0x1
        key 8B  value 8B  max_entries 1  memlock 4096B
37: lpm_trie  flags 0x1
        key 20B  value 8B  max_entries 1  memlock 4096B
125: array  name rx_queue_pckt_c  flags 0x0
        key 4B  value 8B  max_entries 48  memlock 4096B
126: xskmap  name xsks_map  flags 0x0
        key 4B  value 4B  max_entries 64  memlock 4096B

但我认为只有 125和 126与我的程序有关。

队列引导有效，因为使用 sudo bpftool map dump id 125我得到:

key: 00 00 00 00  value: 99 1a cc 04 00 00 00 00
key: 01 00 00 00  value: 00 00 00 00 00 00 00 00
key: 02 00 00 00  value: 00 00 00 00 00 00 00 00
key: 03 00 00 00  value: 00 00 00 00 00 00 00 00
key: 04 00 00 00  value: 00 00 00 00 00 00 00 00
key: 05 00 00 00  value: 00 00 00 00 00 00 00 00
key: 06 00 00 00  value: 00 00 00 00 00 00 00 00
key: 07 00 00 00  value: 00 00 00 00 00 00 00 00
key: 08 00 00 00  value: 00 00 00 00 00 00 00 00
key: 09 00 00 00  value: 00 00 00 00 00 00 00 00
key: 0a 00 00 00  value: 00 00 00 00 00 00 00 00
key: 0b 00 00 00  value: 00 00 00 00 00 00 00 00
key: 0c 00 00 00  value: 00 00 00 00 00 00 00 00
key: 0d 00 00 00  value: 00 00 00 00 00 00 00 00
key: 0e 00 00 00  value: 00 00 00 00 00 00 00 00
key: 0f 00 00 00  value: 00 00 00 00 00 00 00 00
key: 10 00 00 00  value: 00 00 00 00 00 00 00 00
key: 11 00 00 00  value: 00 00 00 00 00 00 00 00
key: 12 00 00 00  value: 00 00 00 00 00 00 00 00
key: 13 00 00 00  value: 00 00 00 00 00 00 00 00
key: 14 00 00 00  value: 00 00 00 00 00 00 00 00
key: 15 00 00 00  value: 00 00 00 00 00 00 00 00
key: 16 00 00 00  value: 00 00 00 00 00 00 00 00
key: 17 00 00 00  value: 00 00 00 00 00 00 00 00
key: 18 00 00 00  value: 00 00 00 00 00 00 00 00
key: 19 00 00 00  value: 00 00 00 00 00 00 00 00
key: 1a 00 00 00  value: 00 00 00 00 00 00 00 00
key: 1b 00 00 00  value: 00 00 00 00 00 00 00 00
key: 1c 00 00 00  value: 00 00 00 00 00 00 00 00
key: 1d 00 00 00  value: 00 00 00 00 00 00 00 00
key: 1e 00 00 00  value: 00 00 00 00 00 00 00 00
key: 1f 00 00 00  value: 00 00 00 00 00 00 00 00
key: 20 00 00 00  value: 00 00 00 00 00 00 00 00
key: 21 00 00 00  value: 00 00 00 00 00 00 00 00
key: 22 00 00 00  value: 00 00 00 00 00 00 00 00
key: 23 00 00 00  value: 00 00 00 00 00 00 00 00
key: 24 00 00 00  value: 00 00 00 00 00 00 00 00
key: 25 00 00 00  value: 00 00 00 00 00 00 00 00
key: 26 00 00 00  value: 00 00 00 00 00 00 00 00
key: 27 00 00 00  value: 00 00 00 00 00 00 00 00
key: 28 00 00 00  value: 00 00 00 00 00 00 00 00
key: 29 00 00 00  value: 00 00 00 00 00 00 00 00
key: 2a 00 00 00  value: 00 00 00 00 00 00 00 00
key: 2b 00 00 00  value: 00 00 00 00 00 00 00 00
key: 2c 00 00 00  value: 00 00 00 00 00 00 00 00
key: 2d 00 00 00  value: 00 00 00 00 00 00 00 00
key: 2e 00 00 00  value: 00 00 00 00 00 00 00 00
key: 2f 00 00 00  value: 00 00 00 00 00 00 00 00
Found 48 elements

如您所见，只有 RX-Queue 0 的计数器大于 0。

但是，如果我看一下 BPF_MAP_TYPE_XSKMAP (用于将数据包传输到用户空间)，我得到:

$ sudo bpftool map dump id 126
key:
00 00 00 00
value:
Operation not supported
key:
01 00 00 00
value:
Operation not supported
key:
02 00 00 00
value:
Operation not supported
key:
03 00 00 00
value:
Operation not supported
key:
04 00 00 00
value:
Operation not supported
...
key:
3e 00 00 00
value:
Operation not supported
key:
3f 00 00 00
value:
Operation not supported
Found 0 elements

是留言 Operation not supported为什么我在用户空间程序中没有收到任何数据包的指示器？或者只是无法在运行时接收值？我也觉得很奇怪看到 Found 0 elements .

任何想法这里有什么问题？

Answer 1

这仅仅是因为类型为 BPF_MAP_TYPE_XSKMAP 的映射不支持从用户空间查找(您将从内核空间获得地址，从用户空间的角度来看这没有意义，并且可能是一个安全问题)。

所以因为尝试查找 returns -EOPNOTSUPP , bpftool 无法显示值。它可能会出错并且不打印任何内容，但我们做到了 print the keys it finds, and print the error messages we get for the values .

至于Found 0 elements ，计数用于 bpftool 可以检索而没有任何错误的元素，因此在这种情况下它保持为零是合乎逻辑的。

因此，您的情况似乎没有任何问题，我认为此输出与您丢失数据包的问题无关。