/* 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 "vmlinux.h"
#include <linux/version.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_core_read.h>

#ifndef PERF_MAX_STACK_DEPTH
#define PERF_MAX_STACK_DEPTH         127
#endif

#define MINBLOCK_US     1
#define MAX_ENTRIES     10000

struct key_t {
        char waker[TASK_COMM_LEN];
        char target[TASK_COMM_LEN];
        u32 wret;
        u32 tret;
};

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

struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __type(key, u32);
        __type(value, u64);
        __uint(max_entries, MAX_ENTRIES);
} start SEC(".maps");

struct wokeby_t {
        char name[TASK_COMM_LEN];
        u32 ret;
};

struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __type(key, u32);
        __type(value, struct wokeby_t);
        __uint(max_entries, MAX_ENTRIES);
} wokeby 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, MAX_ENTRIES);
} stackmap SEC(".maps");

#define STACKID_FLAGS (0 | BPF_F_FAST_STACK_CMP)

SEC("kprobe/try_to_wake_up")
int waker(struct pt_regs *ctx)
{
        struct task_struct *p = (void *)PT_REGS_PARM1_CORE(ctx);
        u32 pid = BPF_CORE_READ(p, pid);
        struct wokeby_t woke;

        bpf_get_current_comm(&woke.name, sizeof(woke.name));
        woke.ret = bpf_get_stackid(ctx, &stackmap, STACKID_FLAGS);

        bpf_map_update_elem(&wokeby, &pid, &woke, BPF_ANY);
        return 0;
}

static inline int update_counts(void *ctx, u32 pid, u64 delta)
{
        struct wokeby_t *woke;
        u64 zero = 0, *val;
        struct key_t key;

        __builtin_memset(&key.waker, 0, sizeof(key.waker));
        bpf_get_current_comm(&key.target, sizeof(key.target));
        key.tret = bpf_get_stackid(ctx, &stackmap, STACKID_FLAGS);
        key.wret = 0;

        woke = bpf_map_lookup_elem(&wokeby, &pid);
        if (woke) {
                key.wret = woke->ret;
                __builtin_memcpy(&key.waker, woke->name, sizeof(key.waker));
                bpf_map_delete_elem(&wokeby, &pid);
        }

        val = bpf_map_lookup_elem(&counts, &key);
        if (!val) {
                bpf_map_update_elem(&counts, &key, &zero, BPF_NOEXIST);
                val = bpf_map_lookup_elem(&counts, &key);
                if (!val)
                        return 0;
        }
        (*val) += delta;
        return 0;
}

#if 1
/* taken from /sys/kernel/tracing/events/sched/sched_switch/format */
SEC("tracepoint/sched/sched_switch")
int oncpu(struct trace_event_raw_sched_switch *ctx)
{
        /* record previous thread sleep time */
        u32 pid = ctx->prev_pid;
#else
SEC("kprobe.multi/finish_task_switch*")
int oncpu(struct pt_regs *ctx)
{
        struct task_struct *p = (void *)PT_REGS_PARM1_CORE(ctx);
        /* record previous thread sleep time */
        u32 pid = BPF_CORE_READ(p, pid);
#endif
        u64 delta, ts, *tsp;

        ts = bpf_ktime_get_ns();
        bpf_map_update_elem(&start, &pid, &ts, BPF_ANY);

        /* calculate current thread's delta time */
        pid = bpf_get_current_pid_tgid();
        tsp = bpf_map_lookup_elem(&start, &pid);
        if (!tsp)
                /* missed start or filtered */
                return 0;

        delta = bpf_ktime_get_ns() - *tsp;
        bpf_map_delete_elem(&start, &pid);
        delta = delta / 1000;
        if (delta < MINBLOCK_US)
                return 0;

        return update_counts(ctx, pid, delta);
}
char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;