eBPF 数据包监视器在“ping -f”时丢失一些数据包

Question

我编写了这个程序来捕获进入我的网络接口的所有数据包。它似乎适用于 ping [IP] 之类的东西。它也适用于 ping -f [IP] -c 10。然而，当被 ping 的数据包数量上升到大约 200 时，程序发现丢失了一些数据包。这是 eBPF 的自然限制还是我做错了什么？这是代码：

此外，当我 ping -f [IP] -c 500 时，它还会输出："Possibly lost 10 samples" 或 "Possibly lost 34 samples"

 from bcc import BPF

# Network interface to be monoitored
INTERFACE = "my_interface"

bpf_text = """
#include <uapi/linux/ptrace.h>
#include <net/sock.h>
#include <bcc/proto.h>
#include <linux/bpf.h>
#define IP_TCP 6
#define IP_UDP 17
#define IP_ICMP 1
#define ETH_HLEN 14
BPF_PERF_OUTPUT(skb_events);    // has to be delcared outside any function
BPF_ARRAY(black_list, u64, 5);
int packet_monitor(struct __sk_buff *skb) {
    u8 *cursor = 0;
    u32 saddr;
    u32 daddr;
    u32 ttl;
    u32 hchecksum;

    u64 magic = 111;
    u64 magic2 = 111;

    struct ethernet_t *ethernet = cursor_advance(cursor, sizeof(*ethernet));
    if (!(ethernet -> type == 0x0800)) {
        return 0; // drop
    }
    struct ip_t *ip = cursor_advance(cursor, sizeof(*ip));
    /*
    if (ip->nextp != IP_TCP) 
    {
        if (ip -> nextp != IP_UDP) 
        {
            if (ip -> nextp != IP_ICMP) 
                return 0; 
        }
    }
    */

    skb_events.perf_submit_skb(skb, skb -> len, &magic, sizeof(magic));
    saddr = ip -> src;
    daddr = ip -> dst;
    ttl = ip -> ttl;
    hchecksum = ip -> hchecksum;
    magic = ip -> src;
    magic2 = ip -> dst;
    skb_events.perf_submit_skb(skb, skb->len, &magic, sizeof(magic)); // this one parses number as a hex to the user space
    skb_events.perf_submit_skb(skb, skb->len, &magic2, sizeof(magic2)); // can send multiple values like this


    bpf_trace_printk("saddr = %llu, daddr = %llu, ttl = %llu", saddr, daddr, ttl); 
//    bpf_trace_printk("Incoming packet!!\n");
    return -1;
}
"""

from ctypes import *
import ctypes as ct
import sys
import socket
import os
import struct

def print_skb_event(cpu, data, size):
    class SkbEvent(ct.Structure):
        _fields_ = [ ("magic", ct.c_uint32), ("magic2", ct.c_uint32)]

    skb_event = ct.cast(data, ct.POINTER(SkbEvent)).contents 
    print("- : ")
    print("%d" % (skb_event.magic))

bpf = BPF(text=bpf_text)

function_skb_matching = bpf.load_func("packet_monitor", BPF.SOCKET_FILTER)

BPF.attach_raw_socket(function_skb_matching, INTERFACE)

bpf["skb_events"].open_perf_buffer(print_skb_event)

black_list = bpf.get_table("black_list")    # retrieve blacklist list

try:
    while True :
        bpf.perf_buffer_poll()  # value = bpf.perf_buffer_poll() function does not return any function and therefore, doesn't work
except KeyboardInterrupt:
    pass

Answer 1

是的，这是性能环形缓冲区的限制。如果 BPF 程序在环形缓冲区上产生事件的速度快于用户空间 (Python) 进程可以消耗它们的速度，那么一些事件将会丢失（因为它是环形缓冲区而被覆盖）。 Possibly lost XX samples 消息是对这种情况的通知。

我首先建议您尝试在 BPF 端将多个 skb_events.perf_submit_skb 调用组合成一个。这可能会有所帮助。否则，您可以尝试在 BPF 端聚合数据，以减少发送到 Python 端的信息。

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