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#include <linux/types.h>
#include <bpf/bpf_endian.h>
#include <bpf/bpf_helpers.h>
#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/pkt_cls.h>
#include <xdp/parsing_helpers.h>
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__type(key, int);
__type(value, int);
__uint(max_entries, 256);
} dummy_redirect_map SEC(".maps");
SEC("tc")
int tc_redirect_map_func(struct __sk_buff *skb) {
int ret = 0;
int action = TC_ACT_OK;
void *data = (void *)(long)skb->data;
void *data_end = (void *)(long)skb->data_end;
bpf_printk("Receive a packet");
#if 0
char key;
unsigned int offset = data_end - data - 1;
ret = bpf_skb_load_bytes(skb, offset, &key, sizeof(key));
if (ret < 0) {
bpf_printk("bpf_skb_load_bytes failed. return code:%d", ret);
action = TC_ACT_OK;
goto out;
}
#endif
// According to the last character, determine which interface to forward the data packet
if (data_end - data < sizeof(struct ethhdr) + 1) {
bpf_printk("Packet length is insufficient");
goto out;
}
/**
* Why do we need to calculate with 0x3fff here?
* Because there's a hole here: when getting the last character, the usual way will fail to load.
* ref:https://github.com/gamemann/Xdp-Access-Last-Byte
*/
__u32 ofs = (data_end - data - 1) & 0x3fff;
void *mgc = data + ofs;
if ((mgc + 1) > data_end) {
bpf_printk("Offset calculation error");
goto out;
}
int key = (int)*(char *)mgc;
bpf_printk("key: %d", key);
// Remove the last character
ret = bpf_skb_change_tail(skb, skb->len - 1, 0);
if (ret < 0) {
bpf_printk("bpf_skb_change_tail failed. return code:%d", ret);
action = TC_ACT_OK;
goto out;
}
const int *ifindex = bpf_map_lookup_elem(&dummy_redirect_map, &key);
if (ifindex == NULL) {
bpf_printk("%d has no corresponding port", key);
action = TC_ACT_OK;
goto out;
}
// Redirect the packet to the endpoint referenced by map at index key.
// action = bpf_redirect(*ifindex, BPF_F_INGRESS);
action = bpf_redirect(*ifindex, 0);
if (action != TC_ACT_REDIRECT) {
bpf_printk("bpf_redirect_map failed. return code:%d", ret);
}
out:
return action;
}
char _license[] SEC("license") = "GPL";
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