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README.md
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bpf_bpfeb.go
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bpf_bpfel.go
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README.md

XDP example 1

Controlplane

  1. It sets a constant mapKey to 0.
  2. It allows the current process to lock memory for eBPF resources.
  3. It loads pre-compiled programs and maps into the kernel.
  4. It attaches the XDP (eXpress Data Path) program to the loopback interface.
  5. It creates a ticker that ticks every second.
  6. It enters a loop where, on each tick of the ticker:
    • It reads the value associated with mapKey from the counter map.
    • It logs the value of the counter.

Dataplane

In this first example I would like to add some more comments:

  1. void *data_end = (void*)(long)ctx->data_end;:

    • This line initializes a pointer data_end to the end of the packet data. It's casting ctx->data_end to a long and then casting it again to a void *.
    • ctx->data_end is a field in the struct xdp_md structure which represents the end of the packet data.

  2. void *data = (void*)(long)ctx->data;:

    • This line initializes a pointer data to the start of the packet data. Similar to data_end, it's casting ctx->data to a long and then casting it again to a void *.
    • ctx->data is a field in the struct xdp_md structure which represents the start of the packet data.

  3. struct ethhdr *eth = data;:

    • This line declares a pointer eth of type struct ethhdr and initializes it with the address of the packet data.
    • struct ethhdr is a structure representing the Ethernet header.

  4. if ((void *)(eth + 1) > data_end) { return 0; }:

    • This condition checks if the Ethernet header extends beyond the end of the packet data.
    • (eth + 1) calculates the address of the next memory location after the Ethernet header.
    • (eth + 1 > data_end) checks if this calculated address is greater than data_end, meaning it's beyond the end of the packet.
    • If the condition is true, it means the Ethernet header extends beyond the packet data, indicating a malformed packet, so it returns 0 to indicate failure.

  5. struct iphdr *ip = (void *)(eth + 1);:

    • This line declares a pointer ip of type struct iphdr and initializes it with the address of the memory location immediately after the Ethernet header.
    • struct iphdr is a structure representing the IP header.

  6. if ((void *)(ip + 1) > data_end) { return 0; }:

    • This condition checks if the IP header extends beyond the end of the packet data.
    • (ip + 1) calculates the address of the next memory location after the IP header.
    • (ip + 1) > data_end) checks if this calculated address is greater than data_end, meaning it's beyond the end of the packet.
    • If the condition is true, it means the IP header extends beyond the packet data, indicating a malformed packet, so it returns 0 to indicate failure.