### Initialize Work-Queue with bpf_wq_init

Source: https://docs.ebpf.io/linux/kfuncs/bpf_wq_init

This example demonstrates the initialization of a work-queue using `bpf_wq_init`. It shows how to set up a `struct bpf_wq` within a map value, initialize it, associate a callback function using `bpf_wq_set_callback`, and then start the work-queue. This is the standard procedure for enabling asynchronous operations in eBPF.

```c
#include <bpf/bpf_helpers.h>

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

struct elem {
    struct bpf_wq w;
};

struct {
    __uint(type, BPF_MAP_TYPE_ARRAY);
    __uint(max_entries, 2);
    __type(key, int);
    __type(value, struct elem);
} array SEC(".maps");

__u32 ok;
__u32 ok_sleepable;
void bpf_kfunc_common_test(void) __ksym;

static int test_elem_callback(void *map, int *key,
        int (callback_fn)(void *map, int *key, struct bpf_wq *wq))
{
    struct elem init = {}, *val;
    struct bpf_wq *wq;

    if ((ok & (1 << *key) ||
        (ok_sleepable & (1 << *key))))
        return -22;

    if (map == &lru &&
        bpf_map_update_elem(map, key, &init, 0))
        return -1;

    val = bpf_map_lookup_elem(map, key);
    if (!val)
        return -2;

    wq = &val->w;
    if (bpf_wq_init(wq, map, 0) != 0)
        return -3;

    if (bpf_wq_set_callback(wq, callback_fn, 0))
        return -4;

    if (bpf_wq_start(wq, 0))
        return -5;

    return 0;
}

/* callback for non sleepable workqueue */
static int wq_callback(void *map, int *key, struct bpf_wq *work)
{
    bpf_kfunc_common_test();
    ok |= (1 << *key);
    return 0;
}

SEC("tc")
long test_call_array_sleepable(void *ctx)
{
    int key = 0;

    return test_elem_callback(&array, &key, wq_cb_sleepable);
}

```

--------------------------------

### BPF_KPROBE Usage Example

Source: https://docs.ebpf.io/ebpf-library/libbpf/ebpf/BPF_KPROBE

An example demonstrating how to use the BPF_KPROBE macro to write a kprobe program that attaches to the start of the `bpf_map_copy_value` function. It shows how to access map types and perf event values.

```c
SEC("kprobe/bpf_map_copy_value")
int BPF_KPROBE(bpf_prog2, struct bpf_map *map)
{
    u32 key = bpf_get_smp_processor_id();
    struct bpf_perf_event_value *val, buf;
    enum bpf_map_type type;
    int error;

    type = BPF_CORE_READ(map, map_type);
    if (type != BPF_MAP_TYPE_HASH)
        return 0;

    error = bpf_perf_event_read_value(&counters, key, &buf, sizeof(buf));
    if (error)
        return 0;

    val = bpf_map_lookup_elem(&values2, &key);
    if (val)
        *val = buf;
    else
        bpf_map_update_elem(&values2, &key, &buf, BPF_NOEXIST);

    return 0;
}
```

--------------------------------

### BPF Crypto Context Creation and Management

Source: https://docs.ebpf.io/linux/kfuncs/bpf_crypto_ctx_create

This example demonstrates the creation of a BPF crypto context using bpf_crypto_ctx_create, its insertion into a map, and subsequent release. It includes necessary includes, map definitions, and a syscall program for setup. The crypto_ctx_insert helper handles updating the map and releasing the old context if one exists.

```c
#include "vmlinux.h"
#include "bpf_tracing_net.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
#include <bpf/bpf_tracing.h>
#include "bpf_misc.h"
#include "bpf_kfuncs.h"

struct bpf_crypto_ctx *bpf_crypto_ctx_create(const struct bpf_crypto_params *params,
                        u32 params__sz, int *err) __ksym;
struct bpf_crypto_ctx *bpf_crypto_acquire(struct bpf_crypto_ctx *ctx) __ksym;
void bpf_crypto_ctx_release(struct bpf_crypto_ctx *ctx) __ksym;

struct __crypto_ctx_value {
    struct bpf_crypto_ctx __kptr * ctx;
};

struct array_map {
    __uint(type, BPF_MAP_TYPE_ARRAY);
    __type(key, int);
    __type(value, struct __crypto_ctx_value);
    __uint(max_entries, 1);
} __crypto_ctx_map SEC(".maps");

static inline int crypto_ctx_insert(struct bpf_crypto_ctx *ctx)
{
    struct __crypto_ctx_value local, *v;
    struct bpf_crypto_ctx *old;
    u32 key = 0;
    int err;

    local.ctx = NULL;
    err = bpf_map_update_elem(&__crypto_ctx_map, &key, &local, 0);
    if (err) {
        bpf_crypto_ctx_release(ctx);
        return err;
    }

    v = bpf_map_lookup_elem(&__crypto_ctx_map, &key);
    if (!v) {
        bpf_crypto_ctx_release(ctx);
        return -ENOENT;
    }

    old = bpf_kptr_xchg(&v->ctx, ctx);
    if (old) {
        bpf_crypto_ctx_release(old);
        return -EEXIST;
    }

    return 0;
}

char cipher[128] = {};
u32 key_len, authsize;
u8 key[256] = {};
int status;

SEC("syscall")
int crypto_setup(void *args)
{
    struct bpf_crypto_ctx *cctx;
    struct bpf_crypto_params params = {
        .type = "skcipher",
        .key_len = key_len,
        .authsize = authsize,
    };
    int err = 0;

    status = 0;

    if (!cipher[0] || !key_len || key_len > 256) {
        status = -EINVAL;
        return 0;
    }

    __builtin_memcpy(&params.algo, cipher, sizeof(cipher));
    __builtin_memcpy(&params.key, key, sizeof(key));
    cctx = bpf_crypto_ctx_create(&params, sizeof(params), &err);

    if (!cctx) {
        status = err;
        return 0;
    }

    err = crypto_ctx_insert(cctx);
    if (err && err != -EEXIST)
        status = err;

    return 0;
}

```

--------------------------------

### Example Usage of __ksym Macro

Source: https://docs.ebpf.io/ebpf-library/libbpf/ebpf/__ksym

Demonstrates how to use the __ksym macro to access kernel symbols like 'bpf_task_storage_busy'. This example shows retrieving the address of a global variable and checking a configuration macro.

```c
// SPDX-License-Identifier: GPL-2.0
/* Copyright (C) 2022. Huawei Technologies Co., Ltd */
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

extern bool CONFIG_PREEMPT __kconfig __weak;
extern const int bpf_task_storage_busy __ksym;

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

int pid = 0;
int busy = 0;

struct {
    __uint(type, BPF_MAP_TYPE_TASK_STORAGE);
    __uint(map_flags, BPF_F_NO_PREALLOC);
    __type(key, int);
    __type(value, long);
} task SEC(".maps");

SEC("raw_tp/sys_enter")
int BPF_PROG(read_bpf_task_storage_busy)
{
    int *value;

    if (!CONFIG_PREEMPT)
        return 0;

    if (bpf_get_current_pid_tgid() >> 32 != pid)
        return 0;

    value = bpf_this_cpu_ptr(&bpf_task_storage_busy);
    if (value)
        busy = *value;

    return 0;

}

```

--------------------------------

### Example kretprobe program using BPF_KRETPROBE

Source: https://docs.ebpf.io/ebpf-library/libbpf/ebpf/BPF_KRETPROBE

An example of a kretprobe program that attaches to the exit of the 'do_unlinkat' function. It logs the process ID and the return value of the function.

```c
SEC("kretprobe/do_unlinkat")
int BPF_KRETPROBE(do_unlinkat_exit, long ret)
{
    pid_t pid;

    pid = bpf_get_current_pid_tgid() >> 32;
    bpf_printk("KPROBE EXIT: pid = %d, ret = %ld\n", pid, ret);
    return 0;
}
```

--------------------------------

### bpf_skb_output Example Usage

Source: https://docs.ebpf.io/linux/helper-function/bpf_skb_output

An example demonstrating how to use the bpf_skb_output helper function within an eBPF program.

```APIDOC
## Example
```c
#include "vmlinux.h"
#include <linux/version.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_core_read.h>

struct {
    __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
    __uint(key_size, sizeof(int));
    __uint(value_size, sizeof(u32));
    __uint(max_entries, 2);
} my_map SEC(".maps");

SEC("tp_btf/netif_receive_skb")
int BPF_PROG(handle_netif_receive_skb, struct sk_buff *skb)
{
    struct S {
        u32 len;
        u64 cookie;
    } data = {};

    data.len = BPF_CORE_READ(skb, len);
    data.cookie = 0x12345678;

    bpf_skb_output(skb, &my_map, 0, &data, sizeof(data));

    return 0;
}

char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;
```
```

--------------------------------

### Get FOU Encapsulation Parameters

Source: https://docs.ebpf.io/linux/kfuncs/bpf_skb_get_fou_encap

This example demonstrates retrieving FOU encapsulation parameters using bpf_skb_get_tunnel_key and bpf_skb_get_fou_encap. It checks if the retrieved destination port matches an expected value and prints tunnel information using bpf_printk. This is suitable for ingress path processing.

```c
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2016 VMware
 * Copyright (c) 2016 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */

SEC("tc")
int ipip_encap_get_tunnel(struct __sk_buff *skb)
{
    int ret;
    struct bpf_tunnel_key key = {};
    struct bpf_fou_encap encap = {};

    ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
    if (ret < 0) {
        log_err(ret);
        return TC_ACT_SHOT;
    }

    ret = bpf_skb_get_fou_encap(skb, &encap);
    if (ret < 0) {
        log_err(ret);
        return TC_ACT_SHOT;
    }

    if (bpf_ntohs(encap.dport) != 5555)
        return TC_ACT_SHOT;

    bpf_printk("%d remote ip 0x%x, sport %d, dport %d\n", ret,
           key.remote_ipv4, bpf_ntohs(encap.sport),
           bpf_ntohs(encap.dport));
    return TC_ACT_OK;
}

```

--------------------------------

### XDP Program Example using SEC

Source: https://docs.ebpf.io/ebpf-library/libbpf/ebpf/SEC

This example demonstrates how to use the `SEC` macro to define an eBPF program that will be placed in the `xdp` ELF section. Programs in this section are typically loaded as `BPF_PROG_TYPE_XDP`.

```c
SEC("xdp")
int example_prog(struct xdp_md *ctx)
{
    void *data_end = (void *)(long)ctx->data_end;
    void *data = (void *)(long)ctx->data;

    if (data + sizeof(struct ethhdr) > data_end)
        return XDP_DROP;

    struct ethhdr *eth = data;
    if (eth->h_proto == htons(ETH_P_IP))
        return XDP_PASS;
}
```

--------------------------------

### Trace Output Example

Source: https://docs.ebpf.io/linux/helper-function/bpf_trace_printk

An example of the typical output format seen in the kernel trace log when bpf_trace_printk is used. This format includes task name, PID, CPU, timestamp, and the formatted message.

```text
telnet-470   [001] .N.. 419421.045894: 0x00000001: <formatted msg>
```

--------------------------------

### Example of bpf_map_create usage

Source: https://docs.ebpf.io/ebpf-library/libbpf/userspace/bpf_map_create

Demonstrates how to use the `bpf_map_create` function to create a BPF hash map. This example shows the necessary parameters for key size, value size, and maximum entries. It also includes basic error handling for map creation.

```c
// struct example_map{
//         __uint(type, BPF_MAP_TYPE_HASH);
//         __uint(max_entries, 10);
//         __type(key, __u32);
//         __type(value, __u32);
// };

int main(){
    int fd = bpf_map_create(
        BPF_MAP_TYPE_HASH,
        NULL,
        sizeof(__u32),
        sizeof(__u32),
        INNER_MAP_MAX_ENTRY,
        NULL
    );
    if(fd < 0)
        puts("error creating map");
}

```

--------------------------------

### Example Usage of bpf_timer_cancel

Source: https://docs.ebpf.io/linux/helper-function/bpf_timer_cancel

This C code demonstrates how to initialize, set a callback for, start, and then cancel a timer using eBPF helper functions. It includes map setup, timer initialization, and callback definition.

```c
#include <linux/bpf.h>
#include <time.h>
#include <stdbool.h>
#include <errno.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

struct elem {
    struct bpf_timer t;
};

struct {
    __uint(type, BPF_MAP_TYPE_ARRAY);
    __uint(max_entries, 1);
    __type(key, int);
    __type(value, struct elem);
} hmap SEC(".maps");

static int timer_callback(void* hmap, int* key, struct bpf_timer *timer)
{
        bpf_printk("Callback was invoked do something useful");
    return 0;
}

SEC("cgroup_skb/egress")
int bpf_prog1(void *ctx)
{
    struct bpf_timer *timer;
    int err, key = 0;
    struct elem init;
    struct elem* ele;

    __builtin_memset(&init, 0, sizeof(struct elem));
    bpf_map_update_elem(&hmap, &key, &init, BPF_ANY);

    ele = bpf_map_lookup_elem(&hmap, &key);
    if (!ele)
        return 1;

    timer = &ele->t;
    err = bpf_timer_init(timer, &hmap, CLOCK_MONOTONIC);
    if (err && err != -EBUSY)
        return 1;

    bpf_timer_set_callback(timer, timer_callback);
    bpf_timer_start(timer, 0, 0);
    bpf_timer_cancel(timer);

    return 0;
}

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

```

--------------------------------

### XDP Entry Point with bpf_dynptr_from_xdp

Source: https://docs.ebpf.io/linux/kfuncs/bpf_dynptr_from_xdp

This is the main XDP program entry point. It uses bpf_dynptr_from_xdp to get a dynamic pointer to the packet, slices the Ethernet header, and then dispatches to handle_ipv4 or handle_ipv6 based on the protocol.

```c
SEC("xdp")
int _xdp_tx_iptunnel(struct xdp_md *xdp)
{
    __u8 buffer[ethhdr_sz];
    struct bpf_dynptr ptr;
    struct ethhdr *eth;
    __u16 h_proto;

    __builtin_memset(buffer, 0, sizeof(buffer));

    bpf_dynptr_from_xdp(xdp, 0, &ptr);
    eth = bpf_dynptr_slice(&ptr, 0, buffer, sizeof(buffer));
    if (!eth)
        return XDP_DROP;

    h_proto = eth->h_proto;

    if (h_proto == bpf_htons(ETH_P_IP))
        return handle_ipv4(xdp, &ptr);
    else if (h_proto == bpf_htons(ETH_P_IPV6))

        return handle_ipv6(xdp, &ptr);
    else
        return XDP_DROP;
}

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

--------------------------------

### eBPF Tracepoint Example: Get and Print Processor ID

Source: https://docs.ebpf.io/linux/helper-function/bpf_get_smp_processor_id

This eBPF program, designed for a tracepoint on syscalls/sys_enter_open, demonstrates how to use bpf_get_smp_processor_id to get the current processor ID and print it using bpf_printk. It requires including vmlinux.h and bpf/bpf_helpers.h.

```c
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>

SEC("tp/syscalls/sys_enter_open")
int sys_open_trace(void *ctx) {
    __u32 processor = bpf_get_smp_processor_id();
    bpf_printk("Executed on processor %u.\n", processor);
    return 0;

}
```

--------------------------------

### init

Source: https://docs.ebpf.io/linux/program-type/BPF_PROG_TYPE_STRUCT_OPS/Qdisc_ops

Initializes a qdisc instance `sch` using the current ops. `arg` contains netlink arguments for creation, and `extack` is for verbose error messages (not usable by BPF qdiscs as of v6.16).

```APIDOC
## init

### Description
This op is called to initialize a qdisc instance `sch` which will use the current ops for its implementation. `arg` are the netlink arguments used to create this new qdisc instance. `extack` is the extended acknowledge, used to carry verbose error messages, which BPF qdiscs cannot utilize as of v6.16.

### Signature
`int (*init)(struct Qdisc *sch, struct nlattr *arg, struct netlink_ext_ack *extack);`
```

--------------------------------

### Example Usage of bpf_core_field_offset

Source: https://docs.ebpf.io/ebpf-library/libbpf/ebpf/bpf_core_field_offset

Demonstrates how to use bpf_core_field_offset within a kprobe to get the byte offset of 'field2' from a 'some_kernel_struct'. The offset is determined at load time.

```c
struct some_kernel_struct {
    __u16 field1; // This field might be smaller or larger on the target kernel
    __u32 field2;
}

SEC("kprobe")
int kprobe__example(struct pt_regs *ctx)
{
    struct some_kernel_struct *a = PT_REGS_PARM1(ctx);
    int field_offset = bpf_core_field_offset(a->field2);

    // Do something with field_offset
    // ...

    return 0;
}
```

--------------------------------

### Example Usage of __kconfig

Source: https://docs.ebpf.io/ebpf-library/libbpf/ebpf/__kconfig

Demonstrates how to use __kconfig to access CONFIG_HZ and adapt time calculations. The loader initializes CONFIG_HZ with the system's kernel configuration value.

```c
extern unsigned CONFIG_HZ __kconfig;

#define USER_HZ     100
#define NSEC_PER_SEC    1000000000ULL
static clock_t jiffies_to_clock_t(unsigned long x)
{
    /* The implementation here tailored to a particular
     * setting of USER_HZ.
     */
    u64 tick_nsec = (NSEC_PER_SEC + CONFIG_HZ/2) / CONFIG_HZ;
    u64 user_hz_nsec = NSEC_PER_SEC / USER_HZ;

    if ((tick_nsec % user_hz_nsec) == 0) {
        if (CONFIG_HZ < USER_HZ)
            return x * (USER_HZ / CONFIG_HZ);
        else
            return x / (CONFIG_HZ / USER_HZ);
    }
    return x * tick_nsec/user_hz_nsec;
}

```

--------------------------------

### Get XFRM Info Example

Source: https://docs.ebpf.io/linux/kfuncs/bpf_skb_get_xfrm_info

Demonstrates how to use bpf_skb_get_xfrm_info to retrieve XFRM metadata and store the interface ID. This snippet is intended for use in TC programs.

```c
// SPDX-License-Identifier: GPL-2.0
#include "vmlinux.h"
#include "bpf_tracing_net.h"
#include <bpf/bpf_helpers.h>

__u32 req_if_id;
__u32 resp_if_id;

int bpf_skb_set_xfrm_info(struct __sk_buff *skb_ctx, 
              const struct bpf_xfrm_info *from) __ksym;
int bpf_skb_get_xfrm_info(struct __sk_buff *skb_ctx, 
              struct bpf_xfrm_info *to) __ksym;

SEC("tc")
int set_xfrm_info(struct __sk_buff *skb)
{
    struct bpf_xfrm_info info = { .if_id = req_if_id };

    return bpf_skb_set_xfrm_info(skb, &info) ? TC_ACT_SHOT : TC_ACT_UNSPEC;
}

SEC("tc")
int get_xfrm_info(struct __sk_buff *skb)
{
    struct bpf_xfrm_info info = {};

    if (bpf_skb_get_xfrm_info(skb, &info) < 0)
        return TC_ACT_SHOT;

    resp_if_id = info.if_id;

    return TC_ACT_UNSPEC;
}

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

```

--------------------------------

### HID BPF Example: Modifying HID Reports

Source: https://docs.ebpf.io/linux/kfuncs/hid_bpf_allocate_context

This example demonstrates modifying HID reports within a BPF program. It uses hid_bpf_allocate_context to get a context, hid_bpf_get_data to access report data, and hid_bpf_hw_request to send reports. The program also includes logic for setting haptic feedback parameters.

```c
// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2022 Benjamin Tissoires
 */

#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include "hid_bpf_helpers.h"

#define HID_UP_BUTTON       0x0009
#define HID_GD_WHEEL        0x0038

SEC("fmod_ret/hid_bpf_device_event")
int BPF_PROG(hid_event, struct hid_bpf_ctx *hctx)
{
    __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 9 /* size */);

    if (!data)
        return 0; /* EPERM check */

    /* Touch */
    data[1] &= 0xfd;

    /* X */
    data[4] = 0;
    data[5] = 0;

    /* Y */
    data[6] = 0;
    data[7] = 0;

    return 0;
}

/* 72 == 360 / 5 -> 1 report every 5 degrees */
int resolution = 72;
int physical = 5;

struct haptic_syscall_args {
    unsigned int hid;
    int retval;
};

static __u8 haptic_data[8];

SEC("syscall")
int set_haptic(struct haptic_syscall_args *args)
{
    struct hid_bpf_ctx *ctx;
    const size_t size = sizeof(haptic_data);
    u16 *res;
    int ret;

    if (size > sizeof(haptic_data))
        return -7; /* -E2BIG */

    ctx = hid_bpf_allocate_context(args->hid);
    if (!ctx)
        return -1; /* EPERM check */

    haptic_data[0] = 1;  /* report ID */

    ret = hid_bpf_hw_request(ctx, haptic_data, size, HID_FEATURE_REPORT, HID_REQ_GET_REPORT);

    bpf_printk("probed/remove event ret value: %d", ret);
    bpf_printk("buf: %02x %02x %02x",
           haptic_data[0],
           haptic_data[1],
           haptic_data[2]);
    bpf_printk("     %02x %02x %02x",
           haptic_data[3],
           haptic_data[4],
           haptic_data[5]);
    bpf_printk("     %02x %02x",
           haptic_data[6],
           haptic_data[7]);

    /* whenever resolution multiplier is not 3600, we have the fixed report descriptor */
    res = (u16 *)&haptic_data[1];
    if (*res != 3600) {
//      haptic_data[1] = 72; /* resolution multiplier */
//      haptic_data[2] = 0;  /* resolution multiplier */
//      haptic_data[3] = 0;  /* Repeat Count */
        haptic_data[4] = 3;  /* haptic Auto Trigger */
//      haptic_data[5] = 5;  /* Waveform Cutoff Time */
//      haptic_data[6] = 80; /* Retrigger Period */
//      haptic_data[7] = 0;  /* Retrigger Period */
    } else {
        haptic_data[4] = 0;
    }

    ret = hid_bpf_hw_request(ctx, haptic_data, size, HID_FEATURE_REPORT, HID_REQ_SET_REPORT);

    bpf_printk("set haptic ret value: %d -> %d", ret, haptic_data[4]);

    args->retval = ret;

    hid_bpf_release_context(ctx);

    return 0;
}

/* Convert REL_DIAL into REL_WHEEL */
SEC("fmod_ret/hid_bpf_rdesc_fixup")
int BPF_PROG(hid_rdesc_fixup, struct hid_bpf_ctx *hctx)
{
    __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */);
    __u16 *res, *phys;

    if (!data)
        return 0; /* EPERM check */

    /* Convert TOUCH into a button */
    data[31] = HID_UP_BUTTON;
    data[33] = 2;

    /* Convert REL_DIAL into REL_WHEEL */
    data[45] = HID_GD_WHEEL;

    /* Change Resolution Multiplier */
    phys = (__u16 *)&data[61];
    *phys = physical;
    res = (__u16 *)&data[66];
    *res = resolution;

    /* Convert X,Y from Abs to Rel */
    data[88] = 0x06;
    data[98] = 0x06;

    return 0;
}

char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = 1;

```

--------------------------------

### Profiling Example with Stack Traces

Source: https://docs.ebpf.io/linux/program-type/BPF_PROG_TYPE_PERF_EVENT

This BPF program collects performance events and records kernel and user-space stack traces. It filters out warmup events and updates a map with counts based on command name and stack IDs. Use this for detailed performance profiling.

```c
/* Copyright (c) 2016 Facebook
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of version 2 of the GNU General Public
* License as published by the Free Software Foundation.
*/
#include <linux/ptrace.h>
#include <uapi/linux/bpf.h>
#include <uapi/linux/bpf_perf_event.h>
#include <uapi/linux/perf_event.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

struct key_t {
    char comm[TASK_COMM_LEN];
    u32 kernstack;
    u32 userstack;
};

struct {
    __uint(type, BPF_MAP_TYPE_HASH);
    __type(key, struct key_t);
    __type(value, u64);
    __uint(max_entries, 10000);
} counts SEC(".maps");

struct {
    __uint(type, BPF_MAP_TYPE_STACK_TRACE);
    __uint(key_size, sizeof(u32));
    __uint(value_size, PERF_MAX_STACK_DEPTH * sizeof(u64));
    __uint(max_entries, 10000);
} stackmap SEC(".maps");

#define KERN_STACKID_FLAGS (0 | BPF_F_FAST_STACK_CMP)
#define USER_STACKID_FLAGS (0 | BPF_F_FAST_STACK_CMP | BPF_F_USER_STACK)

SEC("perf_event")
int bpf_prog1(struct bpf_perf_event_data *ctx)
{
    char time_fmt1[] = "Time Enabled: %llu, Time Running: %llu";
    char time_fmt2[] = "Get Time Failed, ErrCode: %d";
    char addr_fmt[] = "Address recorded on event: %llx";
    char fmt[] = "CPU-%d period %lld ip %llx";
    u32 cpu = bpf_get_smp_processor_id();
    struct bpf_perf_event_value value_buf;
    struct key_t key;
    u64 *val, one = 1;
    int ret;

    if (ctx->sample_period < 10000)
        /* ignore warmup */
        return 0;
    bpf_get_current_comm(&key.comm, sizeof(key.comm));
    key.kernstack = bpf_get_stackid(ctx, &stackmap, KERN_STACKID_FLAGS);
    key.userstack = bpf_get_stackid(ctx, &stackmap, USER_STACKID_FLAGS);
    if ((int)key.kernstack < 0 && (int)key.userstack < 0) {
        bpf_trace_printk(fmt, sizeof(fmt), cpu, ctx->sample_period,
                PT_REGS_IP(&ctx->regs));
        return 0;
    }

    ret = bpf_perf_prog_read_value(ctx, (void *)&value_buf, sizeof(struct bpf_perf_event_value));
    if (!ret)
    bpf_trace_printk(time_fmt1, sizeof(time_fmt1), value_buf.enabled, value_buf.running);
    else
    bpf_trace_printk(time_fmt2, sizeof(time_fmt2), ret);

    if (ctx->addr != 0)
    bpf_trace_printk(addr_fmt, sizeof(addr_fmt), ctx->addr);

    val = bpf_map_lookup_elem(&counts, &key);
    if (val)
        (*val)++;
    else
        bpf_map_update_elem(&counts, &key, &one, BPF_NOEXIST);
    return 0;
}

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

```

--------------------------------

### BPF Ring Buffer and Dynptr Example

Source: https://docs.ebpf.io/linux/helper-function/bpf_ringbuf_discard_dynptr

This example demonstrates the usage of bpf_ringbuf_reserve_dynptr, bpf_dynptr_write, bpf_dynptr_read, bpf_ringbuf_submit_dynptr, and bpf_ringbuf_discard_dynptr. It reserves space in a ring buffer using a dynamic pointer, writes data to it, reads the data back to verify, and then either submits or discards the sample.

```c
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

struct {
    __uint(type, BPF_MAP_TYPE_RINGBUF);
    __uint(max_entries, 256 * 1024);
} ringbuf SEC(".maps");

SEC("tp/syscalls/sys_enter_openat")
int bpf_prog1(void *ctx)
{
    char write_data[64] = "hello there, world!!";
    char read_data[64] = {};
    struct bpf_dynptr ptr;
    int i;
    int local_err = 0;

    local_err = bpf_ringbuf_reserve_dynptr(&ringbuf, sizeof(write_data), 0, &ptr);
    if (local_err < 0)
        goto discard;

    /* Write data into the dynptr */
    local_err = bpf_dynptr_write(&ptr, 0, write_data, sizeof(write_data), 0);
    if (local_err) {
        goto discard;
    }

    /* Read the data that was written into the dynptr */
    local_err = bpf_dynptr_read(read_data, sizeof(read_data), &ptr, 0, 0);
    if (local_err) {
        goto discard;
    }

    /* Ensure the data we read matches the data we wrote */
    for (i = 0; i < sizeof(read_data); i++) {
        if (read_data[i] != write_data[i]) {
            break;
        }
    }
    bpf_printk("Read matches write, dynptr API works");
    bpf_ringbuf_submit_dynptr(&ptr, 0);
    return 0;

discard:
    bpf_ringbuf_discard_dynptr(&ptr, 0);
    return 0;
}

```

--------------------------------

### xsk_ring_prod__fill_addr Usage Example

Source: https://docs.ebpf.io/ebpf-library/libxdp/functions/xsk_ring_prod__fill_addr

This snippet shows the function signature for `xsk_ring_prod__fill_addr`. Use this function to get a pointer to a slot in the fill ring to set the address of a packet buffer.

```c
__u64 *xsk_ring_prod__fill_addr(struct xsk_ring_prod *fill, __u32 idx);

```

--------------------------------

### Get kmem_cache for task_struct

Source: https://docs.ebpf.io/linux/kfuncs/bpf_get_kmem_cache

This example demonstrates how to use bpf_get_kmem_cache to retrieve the kmem_cache for the current task's structure. It then looks up the slab name in a hash map to verify if it's 'task_struct'.

```c
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2024 Google */
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include "bpf_experimental.h"

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

#define SLAB_NAME_MAX  32

struct {
    __uint(type, BPF_MAP_TYPE_HASH);
    __uint(key_size, sizeof(void *));
    __uint(value_size, SLAB_NAME_MAX);
    __uint(max_entries, 1);
} slab_hash SEC(".maps");

extern struct kmem_cache *bpf_get_kmem_cache(u64 addr) __ksym;

/* Result, will be checked by userspace */
int task_struct_found;

SEC("raw_tp/bpf_test_finish")
int BPF_PROG(check_task_struct)
{
    u64 curr = bpf_get_current_task();
    struct kmem_cache *s;
    char *name;

    s = bpf_get_kmem_cache(curr);
    if (s == NULL) {
        task_struct_found = -1;
        return 0;
    }
    name = bpf_map_lookup_elem(&slab_hash, &s);
    if (name && !bpf_strncmp(name, 11, "task_struct"))
        task_struct_found = 1;
    else
        task_struct_found = -2;
    return 0;
}

```

--------------------------------

### Initialize percpu object using bpf_percpu_obj_new

Source: https://docs.ebpf.io/ebpf-library/libbpf/ebpf/__percpu_kptr

Example of initializing a per-CPU object using bpf_percpu_obj_new and associating it with a map element's per-CPU pointer field using bpf_kptr_xchg. If a previous pointer exists, it is dropped.

```c
struct val_t __percpu_kptr *p;
struct elem *e;
int index = 0;

e = bpf_map_lookup_elem(&array, &index);
if (!e)
    return 0;

p = bpf_percpu_obj_new(struct val_t);
if (!p)
    return 0;

p = bpf_kptr_xchg(&e->pc, p);
if (p)
    bpf_percpu_obj_drop(p);

return 0;

```

--------------------------------

### Get Time Elapsed in Nanoseconds

Source: https://docs.ebpf.io/linux/helper-function/bpf_ktime_get_ns

This snippet demonstrates how to use bpf_ktime_get_ns to measure the duration of a task. It captures the start time, performs some operations, and then captures the end time to calculate the elapsed duration.

```c
__u64 start_time = bpf_ktime_get_ns();
/* some tasks */
__u64 end_time = bpf_ktime_get_ns();
__u64 duration = end_time - start_time;

```

--------------------------------

### bpf_wq_start

Source: https://docs.ebpf.io/linux/kfuncs/bpf_wq_start

Starts a work-queue, allowing eBPF programs to schedule work for asynchronous execution. The work-queue must be initialized and have a callback function set prior to calling this kfunc.

```APIDOC
## bpf_wq_start

### Description
Starts a work-queue which allows eBPF programs to schedule work to be executed asynchronously.

### Signature
`int bpf_wq_start(struct bpf_wq *wq, unsigned int flags)`

### Parameters
#### Arguments
- **wq** (`struct bpf_wq *`) - A pointer to a `struct bpf_wq` which must reside in a map value.
- **flags** (`unsigned int`) - Flags to allow for future extensions.

### Returns
- `0` on success.
- A negative error code on failure.
```

--------------------------------

### Get and Filter Tunnel Key Information

Source: https://docs.ebpf.io/linux/helper-function/bpf_skb_get_tunnel_key

Example of using bpf_skb_get_tunnel_key to retrieve tunnel metadata and filter packets based on the remote IPv4 address. This snippet is intended for use in TC ingress programs.

```c
int ret;
struct bpf_tunnel_key key = {};

ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
if (ret < 0)
    return TC_ACT_SHOT; // drop packet

if (key.remote_ipv4 != 0x0a000001)
    return TC_ACT_SHOT; // drop packet

return TC_ACT_OK;       // accept packet

```

--------------------------------

### eBPF Tracepoint Example using bpf_strncmp

Source: https://docs.ebpf.io/linux/helper-function/bpf_strncmp

This snippet demonstrates how to use bpf_strncmp within an eBPF tracepoint program to check if the current task's command name starts with 'cat'. It requires including vmlinux.h and bpf/bpf_helpers.h.

```c
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>

SEC("tp_btf/sys_enter")
int sys_enter_trace(void *ctx) {
  struct task_struct *task = (struct task_struct *)bpf_get_current_task_btf();
  if (bpf_strncmp(task->comm, TASK_COMM_LEN, "cat") != 0) {
    return 0;
  }
  bpf_printk("Hello, I'm a cat!\n");
  return 0;
}

```

--------------------------------

### BPF Cgroup Connect, Getsockname, Getpeername Example

Source: https://docs.ebpf.io/linux/program-type/BPF_PROG_TYPE_CGROUP_SOCK_ADDR

This example demonstrates BPF programs for cgroup connect, getsockname, and getpeername events. It uses bpf_sk_storage to map original service addresses and ports, allowing for service rewiring and exposure.

```c
// SPDX-License-Identifier: GPL-2.0
#include <string.h>
#include <stdbool.h>

#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/in6.h>
#include <sys/socket.h>

#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>

#include <bpf_sockopt_helpers.h>

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

struct svc_addr {
    __be32 addr;
    __be16 port;
};

struct {
    __uint(type, BPF_MAP_TYPE_SK_STORAGE);
    __uint(map_flags, BPF_F_NO_PREALLOC);
    __type(key, int);
    __type(value, struct svc_addr);
} service_mapping SEC ".maps";

SEC("cgroup/connect4")
int connect4(struct bpf_sock_addr *ctx)
{
    struct sockaddr_in sa = {};
    struct svc_addr *orig;

    /* Force local address to 127.0.0.1:22222. */
    sa.sin_family = AF_INET;
    sa.sin_port = bpf_htons(22222);
    sa.sin_addr.s_addr = bpf_htonl(0x7f000001);

    if (bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa)) != 0)
        return 0;

    /* Rewire service 1.2.3.4:60000 to backend 127.0.0.1:60123. */
    if (ctx->user_port == bpf_htons(60000)) {
        orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0,
                    BPF_SK_STORAGE_GET_F_CREATE);
        if (!orig)
            return 0;

        orig->addr = ctx->user_ip4;
        orig->port = ctx->user_port;

        ctx->user_ip4 = bpf_htonl(0x7f000001);
        ctx->user_port = bpf_htons(60123);
    }
    return 1;
}

SEC("cgroup/getsockname4")
int getsockname4(struct bpf_sock_addr *ctx)
{
    if (!get_set_sk_priority(ctx))
        return 1;

    /* Expose local server as 1.2.3.4:60000 to client. */
    if (ctx->user_port == bpf_htons(60123)) {
        ctx->user_ip4 = bpf_htonl(0x01020304);
        ctx->user_port = bpf_htons(60000);
    }
    return 1;
}

SEC("cgroup/getpeername4")
int getpeername4(struct bpf_sock_addr *ctx)
{
    struct svc_addr *orig;

    if (!get_set_sk_priority(ctx))
        return 1;

    /* Expose service 1.2.3.4:60000 as peer instead of backend. */
    if (ctx->user_port == bpf_htons(60123)) {
        orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0, 0);
        if (orig) {
            ctx->user_ip4 = orig->addr;
            ctx->user_port = orig->port;
        }
    }
    return 1;
}

```

--------------------------------

### Get Boot Time in Nanoseconds

Source: https://docs.ebpf.io/linux/helper-function/bpf_ktime_get_boot_ns

This snippet demonstrates how to use bpf_ktime_get_boot_ns to capture a start time, perform some tasks, and then capture an end time to calculate a duration. It is useful for measuring time intervals within eBPF programs.

```c
__u64 start_time = bpf_ktime_get_boot_ns();
/* some tasks */
__u64 end_time = bpf_ktime_get_boot_ns();
__u64 duration = end_time - start_time;

```

--------------------------------

### bpf_wq_init

Source: https://docs.ebpf.io/linux/kfuncs/bpf_wq_init

Initializes a work-queue for asynchronous execution. This is the first step in using a work-queue, followed by setting a callback and starting the work.

```APIDOC
## bpf_wq_init

### Description
Initializes a work-queue which allows eBPF programs to schedule work to be executed asynchronously.

### Signature
`int bpf_wq_init(struct bpf_wq *wq, void *p__map, unsigned int flags)`

### Parameters
* `wq` (struct bpf_wq *): A pointer to a `struct bpf_wq` which must reside in a map value.
* `p__map` (void *): A pointer to a map that contains the `wq` as value.
* `flags` (unsigned int): Flags to allow for future extensions.

### Returns
* `0` on success.
* A negative error code on failure.
```

--------------------------------

### Lookup Element in Per-CPU Map

Source: https://docs.ebpf.io/linux/helper-function/bpf_map_lookup_percpu_elem

This example demonstrates how to use bpf_map_lookup_percpu_elem to retrieve a value from a per-CPU map. It first gets the current CPU ID and then attempts to look up the element using the provided key. The result is printed to the eBPF log.

```c
int key, *value, cpuid;
key=0;
cpuid=bpf_get_smp_processor_id();
value = bpf_map_lookup_percpu_elem(&percpu_map, &key, cpuid);
if (value)
    bpf_printk("Read value '%d' from the map on CPU '%d'\n", *value, cpuid);
else
    bpf_printk("Failed to read value from the map\n");

```

--------------------------------

### Set FOU Encapsulation Parameters

Source: https://docs.ebpf.io/linux/kfuncs/bpf_skb_set_fou_encap

This example demonstrates setting up FOU encapsulation for packets. It first sets tunnel key information and then configures the FOU encapsulation with a specific destination port and auto-assigned source port. Ensure `bpf_skb_set_tunnel_key` is called successfully before this function.

```c
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2016 VMware
 * Copyright (c) 2016 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */

SEC("tc")
int ipip_fou_set_tunnel(struct __sk_buff *skb)
{
    struct bpf_tunnel_key key = {};
    struct bpf_fou_encap encap = {};
    void *data = (void *)(long)skb->data;
    struct iphdr *iph = data;
    void *data_end = (void *)(long)skb->data_end;
    int ret;

    if (data + sizeof(*iph) > data_end) {
        log_err(1);
        return TC_ACT_SHOT;
    }

    key.tunnel_ttl = 64;
    if (iph->protocol == IPPROTO_ICMP)
        key.remote_ipv4 = 0xac100164; /* 172.16.1.100 */

    ret = bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
    if (ret < 0) {
        log_err(ret);
        return TC_ACT_SHOT;
    }

    encap.sport = 0;
    encap.dport = bpf_htons(5555);

    ret = bpf_skb_set_fou_encap(skb, &encap, FOU_BPF_ENCAP_FOU);
    if (ret < 0) {
        log_err(ret);
        return TC_ACT_SHOT;
    }

    return TC_ACT_OK;
}

```