Add xdp_kern

packet-exchange/build/Makefile

@@ -11,6 +11,7 @@ CLIENT_SRCS  = client.c
 CLIENT_SRCS += recv_packet.c
 CLIENT_SRCS += send_packet.c
 CLIENT_SRCS += utilities.c
+CLIENT_SRCS += xdp_kern.c
 
 SERVER_OBJS = $(SERVER_SRCS:%.c=%.o)
 CLIENT_OBJS = $(CLIENT_SRCS:%.c=%.o)

packet-exchange/src/xdp_kern.c

+#define KBUILD_MODNAME "blub"
+
+#include <linux/bpf.h>
+#include <linux/if_link.h>
+#include <linux/if_xdp.h>
+#include <linux/if_ether.h>
+#include <linux/udp.h>
+#include <linux/ip.h>
+#include <linux/in.h>
+
+#include "bpf_helpers.h"
+
+struct bpf_map_def SEC("maps") xsks_map = {
+    .type        = BPF_MAP_TYPE_XSKMAP,
+    .key_size    = sizeof(int),
+    .value_size  = sizeof(int),
+    .max_entries = 64,
+};
+
+static inline int parse_ipv4(void *data, unsigned long long nh_off,
+                             void *data_end)
+{
+    struct iphdr *iph = data + nh_off;
+
+    if ((void *)(iph + 1) > data_end)
+        return 0;
+
+    return iph->protocol;
+}
+
+SEC("xdp_sock")
+int xdp_sock_prog(struct xdp_md *ctx)
+{
+    void *data_end = (void *)(long)ctx->data_end;
+    void *data = (void *)(long)ctx->data;
+    struct ethhdr *eth = data;
+    int idx = ctx->rx_queue_index;
+    unsigned int ipproto = 0;
+    unsigned long long nh_off;
+
+    /* Check if it's a UDP frame: If UDP -> Redirect to active xsk for user
+     * space. If not -> pass to stack.
+     */
+    nh_off = sizeof(*eth);
+    if (data + nh_off > data_end)
+        return XDP_PASS;
+
+    if (eth->h_proto == __builtin_bswap16(ETH_P_IP))
+        ipproto = parse_ipv4(data, nh_off, data_end);
+
+    if (ipproto != IPPROTO_UDP)
+        return XDP_PASS;
+
+    /* If socket bound to rx_queue than redirect to user space */
+    if (bpf_map_lookup_elem(&xsks_map, &idx))
+        return bpf_redirect_map(&xsks_map, idx, 0);
+
+    /* Else pass to Linux' network stack */
+    return XDP_PASS;
+}
+
+char _license[] SEC("license") = "GPL";