// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
// Copyright (c) 2021 Google
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

// This should be in sync with "util/ftrace.h"
#define NUM_BUCKET  22

struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __uint(key_size, sizeof(__u64));
        __uint(value_size, sizeof(__u64));
        __uint(max_entries, 10000);
} functime SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __uint(key_size, sizeof(__u32));
        __uint(value_size, sizeof(__u8));
        __uint(max_entries, 1);
} cpu_filter SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __uint(key_size, sizeof(__u32));
        __uint(value_size, sizeof(__u8));
        __uint(max_entries, 1);
} task_filter SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
        __uint(key_size, sizeof(__u32));
        __uint(value_size, sizeof(__u64));
        __uint(max_entries, NUM_BUCKET);
} latency SEC(".maps");


int enabled = 0;

// stats
__s64 total;
__s64 count;
__s64 max;
__s64 min;

const volatile int has_cpu = 0;
const volatile int has_task = 0;
const volatile int use_nsec = 0;
const volatile unsigned int bucket_range;
const volatile unsigned int min_latency;
const volatile unsigned int max_latency;
const volatile unsigned int bucket_num = NUM_BUCKET;

static bool can_record(void)
{
        if (has_cpu) {
                __u32 cpu = bpf_get_smp_processor_id();
                __u8 *ok;

                ok = bpf_map_lookup_elem(&cpu_filter, &cpu);
                if (!ok)
                        return false;
        }

        if (has_task) {
                __u32 pid = bpf_get_current_pid_tgid();
                __u8 *ok;

                ok = bpf_map_lookup_elem(&task_filter, &pid);
                if (!ok)
                        return false;
        }
        return true;
}

static void update_latency(__s64 delta)
{
        __u64 val = delta;
        __u32 key = 0;
        __u64 *hist;
        __u64 cmp_base = use_nsec ? 1 : 1000;

        if (delta < 0)
                return;

        if (bucket_range != 0) {
                val = delta / cmp_base;

                if (min_latency > 0) {
                        if (val > min_latency)
                                val -= min_latency;
                        else
                                goto do_lookup;
                }

                // Less than 1 unit (ms or ns), or, in the future,
                // than the min latency desired.
                if (val > 0) { // 1st entry: [ 1 unit .. bucket_range units )
                        key = val / bucket_range + 1;
                        if (key >= bucket_num)
                                key = bucket_num - 1;
                }

                goto do_lookup;
        }
        // calculate index using delta
        for (key = 0; key < (bucket_num - 1); key++) {
                if (delta < (cmp_base << key))
                        break;
        }

do_lookup:
        hist = bpf_map_lookup_elem(&latency, &key);
        if (!hist)
                return;

        __sync_fetch_and_add(hist, 1);

        __sync_fetch_and_add(&total, delta); // always in nsec
        __sync_fetch_and_add(&count, 1);

        if (delta > max)
                max = delta;
        if (delta < min)
                min = delta;
}

SEC("kprobe/func")
int BPF_PROG(func_begin)
{
        __u64 key, now;

        if (!enabled || !can_record())
                return 0;

        key = bpf_get_current_pid_tgid();
        now = bpf_ktime_get_ns();

        // overwrite timestamp for nested functions
        bpf_map_update_elem(&functime, &key, &now, BPF_ANY);
        return 0;
}

SEC("kretprobe/func")
int BPF_PROG(func_end)
{
        __u64 tid;
        __u64 *start;

        if (!enabled)
                return 0;

        tid = bpf_get_current_pid_tgid();

        start = bpf_map_lookup_elem(&functime, &tid);
        if (start) {
                update_latency(bpf_ktime_get_ns() - *start);
                bpf_map_delete_elem(&functime, &tid);
        }

        return 0;
}

SEC("raw_tp")
int BPF_PROG(event_begin)
{
        __u64 key, now;

        if (!enabled || !can_record())
                return 0;

        key = bpf_get_current_pid_tgid();
        now = bpf_ktime_get_ns();

        // overwrite timestamp for nested events
        bpf_map_update_elem(&functime, &key, &now, BPF_ANY);
        return 0;
}

SEC("raw_tp")
int BPF_PROG(event_end)
{
        __u64 tid;
        __u64 *start;

        if (!enabled)
                return 0;

        tid = bpf_get_current_pid_tgid();

        start = bpf_map_lookup_elem(&functime, &tid);
        if (start) {
                update_latency(bpf_ktime_get_ns() - *start);
                bpf_map_delete_elem(&functime, &tid);
        }

        return 0;
}