// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2019 Facebook
#include <linux/bpf.h>
#include <stdbool.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
#include <bpf/bpf_tracing.h>

char _license[] SEC("license") = "GPL";
struct {
        __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
        __type(key, int);
        __type(value, int);
} perf_buf_map SEC(".maps");

#define _(P) (__builtin_preserve_access_index(P))

/* define few struct-s that bpf program needs to access */
struct callback_head {
        struct callback_head *next;
        void (*func)(struct callback_head *head);
};
struct dev_ifalias {
        struct callback_head rcuhead;
};

struct net_device /* same as kernel's struct net_device */ {
        int ifindex;
        struct dev_ifalias *ifalias;
};

typedef struct {
        int counter;
} atomic_t;
typedef struct refcount_struct {
        atomic_t refs;
} refcount_t;

struct sk_buff {
        /* field names and sizes should match to those in the kernel */
        unsigned int len, data_len;
        __u16 mac_len, hdr_len, queue_mapping;
        struct net_device *dev;
        /* order of the fields doesn't matter */
        refcount_t users;
        unsigned char *data;
        char __pkt_type_offset[0];
        char cb[48];
};

struct meta {
        int ifindex;
        __u32 cb32_0;
        __u8 cb8_0;
};

/* TRACE_EVENT(kfree_skb,
 *         TP_PROTO(struct sk_buff *skb, void *location),
 */
SEC("tp_btf/kfree_skb")
int BPF_PROG(trace_kfree_skb, struct sk_buff *skb, void *location)
{
        struct net_device *dev;
        struct callback_head *ptr;
        void *func;
        int users;
        unsigned char *data;
        unsigned short pkt_data;
        struct meta meta = {};
        char pkt_type;
        __u32 *cb32;
        __u8 *cb8;

        __builtin_preserve_access_index(({
                users = skb->users.refs.counter;
                data = skb->data;
                dev = skb->dev;
                ptr = dev->ifalias->rcuhead.next;
                func = ptr->func;
                cb8 = (__u8 *)&skb->cb;
                cb32 = (__u32 *)&skb->cb;
        }));

        meta.ifindex = _(dev->ifindex);
        meta.cb8_0 = cb8[8];
        meta.cb32_0 = cb32[2];

        bpf_probe_read_kernel(&pkt_type, sizeof(pkt_type), _(&skb->__pkt_type_offset));
        pkt_type &= 7;

        /* read eth proto */
        bpf_probe_read_kernel(&pkt_data, sizeof(pkt_data), data + 12);

        bpf_printk("rcuhead.next %llx func %llx\n", ptr, func);
        bpf_printk("skb->len %d users %d pkt_type %x\n",
                   _(skb->len), users, pkt_type);
        bpf_printk("skb->queue_mapping %d\n", _(skb->queue_mapping));
        bpf_printk("dev->ifindex %d data %llx pkt_data %x\n",
                   meta.ifindex, data, pkt_data);
        bpf_printk("cb8_0:%x cb32_0:%x\n", meta.cb8_0, meta.cb32_0);

        if (users != 1 || pkt_data != bpf_htons(0x86dd) || meta.ifindex != 1)
                /* raw tp ignores return value */
                return 0;

        /* send first 72 byte of the packet to user space */
        bpf_skb_output(skb, &perf_buf_map, (72ull << 32) | BPF_F_CURRENT_CPU,
                       &meta, sizeof(meta));
        return 0;
}

struct {
        bool fentry_test_ok;
        bool fexit_test_ok;
} result = {};

SEC("fentry/eth_type_trans")
int BPF_PROG(fentry_eth_type_trans, struct sk_buff *skb, struct net_device *dev,
             unsigned short protocol)
{
        int len, ifindex;

        __builtin_preserve_access_index(({
                len = skb->len;
                ifindex = dev->ifindex;
        }));

        /* fentry sees full packet including L2 header */
        if (len != 74 || ifindex != 1)
                return 0;
        result.fentry_test_ok = true;
        return 0;
}

SEC("fexit/eth_type_trans")
int BPF_PROG(fexit_eth_type_trans, struct sk_buff *skb, struct net_device *dev,
             unsigned short protocol)
{
        int len, ifindex;

        __builtin_preserve_access_index(({
                len = skb->len;
                ifindex = dev->ifindex;
        }));

        /* fexit sees packet without L2 header that eth_type_trans should have
         * consumed.
         */
        if (len != 60 || protocol != bpf_htons(0x86dd) || ifindex != 1)
                return 0;
        result.fexit_test_ok = true;
        return 0;
}