// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
// Copyright (c) 2020 Facebook
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

/* map of perf event fds, num_cpu * num_metric entries */
struct {
        __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
        __uint(key_size, sizeof(__u32));
        __uint(value_size, sizeof(int));
} events SEC(".maps");

/* readings at fentry */
struct {
        __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
        __uint(key_size, sizeof(__u32));
        __uint(value_size, sizeof(struct bpf_perf_event_value));
        __uint(max_entries, 1);
} fentry_readings SEC(".maps");

/* accumulated readings */
struct {
        __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
        __uint(key_size, sizeof(__u32));
        __uint(value_size, sizeof(struct bpf_perf_event_value));
        __uint(max_entries, 1);
} accum_readings SEC(".maps");

const volatile __u32 num_cpu = 1;

SEC("fentry/XXX")
int BPF_PROG(fentry_XXX)
{
        __u32 key = bpf_get_smp_processor_id();
        struct bpf_perf_event_value *ptr;
        __u32 zero = 0;
        long err;

        /* look up before reading, to reduce error */
        ptr = bpf_map_lookup_elem(&fentry_readings, &zero);
        if (!ptr)
                return 0;

        err = bpf_perf_event_read_value(&events, key, ptr, sizeof(*ptr));
        if (err)
                return 0;

        return 0;
}

static inline void
fexit_update_maps(struct bpf_perf_event_value *after)
{
        struct bpf_perf_event_value *before, diff;
        __u32 zero = 0;

        before = bpf_map_lookup_elem(&fentry_readings, &zero);
        /* only account samples with a valid fentry_reading */
        if (before && before->counter) {
                struct bpf_perf_event_value *accum;

                diff.counter = after->counter - before->counter;
                diff.enabled = after->enabled - before->enabled;
                diff.running = after->running - before->running;

                accum = bpf_map_lookup_elem(&accum_readings, &zero);
                if (accum) {
                        accum->counter += diff.counter;
                        accum->enabled += diff.enabled;
                        accum->running += diff.running;
                }
        }
}

SEC("fexit/XXX")
int BPF_PROG(fexit_XXX)
{
        struct bpf_perf_event_value reading;
        __u32 cpu = bpf_get_smp_processor_id();
        int err;

        /* read all events before updating the maps, to reduce error */
        err = bpf_perf_event_read_value(&events, cpu, &reading, sizeof(reading));
        if (err)
                return 0;

        fexit_update_maps(&reading);
        return 0;
}

char LICENSE[] SEC("license") = "Dual BSD/GPL";