feat:non struct field values can be cast

tests/c-form/xdp_test.bpf.c

@@ -0,0 +1,72 @@
+// xdp_ip_map.c
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+#include <linux/if_ether.h>
+#include <linux/ip.h>
+
+struct ip_key {
+   __u8 family;     // 4 = IPv4
+   __u8 pad[3];     // padding for alignment
+   __u8 addr[16];   // IPv4 uses first 4 bytes
+};
+
+// key → packet count
+struct {
+   __uint(type, BPF_MAP_TYPE_HASH);
+   __uint(max_entries, 16384);
+   __type(key, struct ip_key);
+   __type(value, __u64);
+} ip_count_map SEC(".maps");
+
+SEC("xdp")
+int xdp_ip_map(struct xdp_md *ctx)
+{
+   void *data_end = (void *)(long)ctx->data_end;
+   void *data     = (void *)(long)ctx->data;
+   struct ethhdr *eth = data;
+
+   if (eth + 1 > (struct ethhdr *)data_end)
+       return XDP_PASS;
+
+   __u16 h_proto = eth->h_proto;
+   void *nh = data + sizeof(*eth);
+
+   // VLAN handling: single tag
+   if (h_proto == bpf_htons(ETH_P_8021Q) ||
+       h_proto == bpf_htons(ETH_P_8021AD)) {
+
+       if (nh + 4 > data_end)
+           return XDP_PASS;
+
+       h_proto = *(__u16 *)(nh + 2);
+       nh += 4;
+   }
+
+   struct ip_key key = {};
+
+   // IPv4
+   if (h_proto == bpf_htons(ETH_P_IP)) {
+       struct iphdr *iph = nh;
+       if (iph + 1 > (struct iphdr *)data_end)
+           return XDP_PASS;
+
+       key.family = 4;
+       // Copy 4 bytes of IPv4 address
+       __builtin_memcpy(key.addr, &iph->saddr, 4);
+
+       __u64 *val = bpf_map_lookup_elem(&ip_count_map, &key);
+       if (val)
+           (*val)++;
+       else {
+           __u64 init = 1;
+           bpf_map_update_elem(&ip_count_map, &key, &init, BPF_ANY);
+       }
+
+       return XDP_PASS;
+   }
+
+   return XDP_PASS;
+}
+
+char _license[] SEC("license") = "GPL";