// SPDX-License-Identifier: GPL-2.0

#include <stddef.h>
#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/udp.h>
#include <linux/tcp.h>
#include <bpf/bpf_endian.h>
#include <bpf/bpf_helpers.h>

enum {
        XDP_PORT = 1,
        XDP_PROTO = 4,
} xdp_map_setup_keys;

struct {
        __uint(type, BPF_MAP_TYPE_ARRAY);
        __uint(max_entries, 5);
        __type(key, __u32);
        __type(value, __s32);
} map_xdp_setup SEC(".maps");

/* RSS hash results: key 0 = hash, key 1 = hash type,
 * key 2 = packet count, key 3 = error count.
 */
enum {
        RSS_KEY_HASH = 0,
        RSS_KEY_TYPE = 1,
        RSS_KEY_PKT_CNT = 2,
        RSS_KEY_ERR_CNT = 3,
};

struct {
        __uint(type, BPF_MAP_TYPE_ARRAY);
        __type(key, __u32);
        __type(value, __u32);
        __uint(max_entries, 4);
} map_rss SEC(".maps");

/* Mirror of enum xdp_rss_hash_type from include/net/xdp.h.
 * Needed because the enum is not part of UAPI headers.
 */
enum xdp_rss_hash_type {
        XDP_RSS_L3_IPV4 = 1U << 0,
        XDP_RSS_L3_IPV6 = 1U << 1,
        XDP_RSS_L3_DYNHDR = 1U << 2,
        XDP_RSS_L4 = 1U << 3,
        XDP_RSS_L4_TCP = 1U << 4,
        XDP_RSS_L4_UDP = 1U << 5,
        XDP_RSS_L4_SCTP = 1U << 6,
        XDP_RSS_L4_IPSEC = 1U << 7,
        XDP_RSS_L4_ICMP = 1U << 8,
};

extern int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, __u32 *hash,
                                    enum xdp_rss_hash_type *rss_type) __ksym;

static __always_inline __u16 get_dest_port(void *l4, void *data_end,
                                           __u8 protocol)
{
        if (protocol == IPPROTO_UDP) {
                struct udphdr *udp = l4;

                if ((void *)(udp + 1) > data_end)
                        return 0;
                return udp->dest;
        } else if (protocol == IPPROTO_TCP) {
                struct tcphdr *tcp = l4;

                if ((void *)(tcp + 1) > data_end)
                        return 0;
                return tcp->dest;
        }

        return 0;
}

SEC("xdp")
int xdp_rss_hash(struct xdp_md *ctx)
{
        void *data_end = (void *)(long)ctx->data_end;
        void *data = (void *)(long)ctx->data;
        enum xdp_rss_hash_type rss_type = 0;
        struct ethhdr *eth = data;
        __u8 l4_proto = 0;
        __u32 hash = 0;
        __u32 key, val;
        void *l4 = NULL;
        __u32 *cnt;
        int ret;

        if ((void *)(eth + 1) > data_end)
                return XDP_PASS;

        if (eth->h_proto == bpf_htons(ETH_P_IP)) {
                struct iphdr *iph = (void *)(eth + 1);

                if ((void *)(iph + 1) > data_end)
                        return XDP_PASS;
                l4_proto = iph->protocol;
                l4 = (void *)(iph + 1);
        } else if (eth->h_proto == bpf_htons(ETH_P_IPV6)) {
                struct ipv6hdr *ip6h = (void *)(eth + 1);

                if ((void *)(ip6h + 1) > data_end)
                        return XDP_PASS;
                l4_proto = ip6h->nexthdr;
                l4 = (void *)(ip6h + 1);
        }

        if (!l4)
                return XDP_PASS;

        /* Filter on the configured protocol (map_xdp_setup key XDP_PROTO).
         * When set, only process packets matching the requested L4 protocol.
         */
        key = XDP_PROTO;
        __s32 *proto_cfg = bpf_map_lookup_elem(&map_xdp_setup, &key);

        if (proto_cfg && *proto_cfg != 0 && l4_proto != (__u8)*proto_cfg)
                return XDP_PASS;

        /* Filter on the configured port (map_xdp_setup key XDP_PORT).
         * Only applies to protocols with ports (UDP, TCP).
         */
        key = XDP_PORT;
        __s32 *port_cfg = bpf_map_lookup_elem(&map_xdp_setup, &key);

        if (port_cfg && *port_cfg != 0) {
                __u16 dest = get_dest_port(l4, data_end, l4_proto);

                if (!dest || bpf_ntohs(dest) != (__u16)*port_cfg)
                        return XDP_PASS;
        }

        ret = bpf_xdp_metadata_rx_hash(ctx, &hash, &rss_type);
        if (ret < 0) {
                key = RSS_KEY_ERR_CNT;
                cnt = bpf_map_lookup_elem(&map_rss, &key);
                if (cnt)
                        __sync_fetch_and_add(cnt, 1);
                return XDP_PASS;
        }

        key = RSS_KEY_HASH;
        bpf_map_update_elem(&map_rss, &key, &hash, BPF_ANY);

        key = RSS_KEY_TYPE;
        val = (__u32)rss_type;
        bpf_map_update_elem(&map_rss, &key, &val, BPF_ANY);

        key = RSS_KEY_PKT_CNT;
        cnt = bpf_map_lookup_elem(&map_rss, &key);
        if (cnt)
                __sync_fetch_and_add(cnt, 1);

        return XDP_PASS;
}

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