// SPDX-License-Identifier: GPL-2.0
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#include <stdint.h>
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#include <linux/bpf.h>
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#include <linux/if_ether.h>
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#include <linux/stddef.h>
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#include <linux/in.h>
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#include <linux/ip.h>
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#include <linux/pkt_cls.h>
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#include <linux/tcp.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_endian.h>
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/* the maximum delay we are willing to add (drop packets beyond that) */
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#define TIME_HORIZON_NS (2000 * 1000 * 1000)
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#define NS_PER_SEC 1000000000
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#define ECN_HORIZON_NS 5000000
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#define THROTTLE_RATE_BPS (5 * 1000 * 1000)
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/* flow_key => last_tstamp timestamp used */
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struct bpf_map_def SEC("maps") flow_map = {
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.type = BPF_MAP_TYPE_HASH,
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.key_size = sizeof(uint32_t),
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.value_size = sizeof(uint64_t),
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.max_entries = 1,
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};
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static inline int throttle_flow(struct __sk_buff *skb)
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{
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int key = 0;
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uint64_t *last_tstamp = bpf_map_lookup_elem(&flow_map, &key);
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uint64_t delay_ns = ((uint64_t)skb->len) * NS_PER_SEC /
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THROTTLE_RATE_BPS;
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uint64_t now = bpf_ktime_get_ns();
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uint64_t tstamp, next_tstamp = 0;
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if (last_tstamp)
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next_tstamp = *last_tstamp + delay_ns;
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tstamp = skb->tstamp;
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if (tstamp < now)
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tstamp = now;
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/* should we throttle? */
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if (next_tstamp <= tstamp) {
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if (bpf_map_update_elem(&flow_map, &key, &tstamp, BPF_ANY))
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return TC_ACT_SHOT;
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return TC_ACT_OK;
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}
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/* do not queue past the time horizon */
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if (next_tstamp - now >= TIME_HORIZON_NS)
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return TC_ACT_SHOT;
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/* set ecn bit, if needed */
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if (next_tstamp - now >= ECN_HORIZON_NS)
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bpf_skb_ecn_set_ce(skb);
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if (bpf_map_update_elem(&flow_map, &key, &next_tstamp, BPF_EXIST))
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return TC_ACT_SHOT;
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skb->tstamp = next_tstamp;
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return TC_ACT_OK;
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}
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static inline int handle_tcp(struct __sk_buff *skb, struct tcphdr *tcp)
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{
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void *data_end = (void *)(long)skb->data_end;
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/* drop malformed packets */
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if ((void *)(tcp + 1) > data_end)
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return TC_ACT_SHOT;
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if (tcp->dest == bpf_htons(9000))
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return throttle_flow(skb);
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return TC_ACT_OK;
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}
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static inline int handle_ipv4(struct __sk_buff *skb)
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{
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void *data_end = (void *)(long)skb->data_end;
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void *data = (void *)(long)skb->data;
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struct iphdr *iph;
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uint32_t ihl;
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/* drop malformed packets */
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if (data + sizeof(struct ethhdr) > data_end)
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return TC_ACT_SHOT;
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iph = (struct iphdr *)(data + sizeof(struct ethhdr));
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if ((void *)(iph + 1) > data_end)
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return TC_ACT_SHOT;
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ihl = iph->ihl * 4;
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if (((void *)iph) + ihl > data_end)
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return TC_ACT_SHOT;
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if (iph->protocol == IPPROTO_TCP)
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return handle_tcp(skb, (struct tcphdr *)(((void *)iph) + ihl));
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return TC_ACT_OK;
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}
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SEC("cls_test") int tc_prog(struct __sk_buff *skb)
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{
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if (skb->protocol == bpf_htons(ETH_P_IP))
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return handle_ipv4(skb);
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return TC_ACT_OK;
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}
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char __license[] SEC("license") = "GPL";
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