ebpf_example.c

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>

// Define a per-CPU array map to keep the packet count
struct {
    __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
    __uint(key_size, sizeof(__u32));
    __uint(value_size, sizeof(__u64));
    __uint(max_entries, 1);
} packet_count SEC(".maps");

SEC("xdp")
int count_packets(struct xdp_md *ctx) {
    __u32 key = 0; // Single key, since we have only one entry
    __u64 init_val = 0;
    __u64 *value;

    // Look up the value of the packet count for the given key
    value = bpf_map_lookup_elem(&packet_count, &key);
    if (value) {
        // Increment the packet count
        *value += 1;
    } else {
        // Initialize the packet count if not found (though this should not happen with PERCPU_ARRAY)
        bpf_map_update_elem(&packet_count, &key, &init_val, BPF_ANY);
    }

    return XDP_PASS; // Allow the packet to pass through
}

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