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

#define MAX_ENTRIES 102400

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);
} diff_readings SEC(".maps");

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");

struct {
	__uint(type, BPF_MAP_TYPE_HASH);
	__uint(key_size, sizeof(__u32));
	__uint(value_size, sizeof(struct bperf_filter_value));
	__uint(max_entries, MAX_ENTRIES);
	__uint(map_flags, BPF_F_NO_PREALLOC);
} filter SEC(".maps");

enum bperf_filter_type type = 0;
int enabled = 0;
int inherit;

SEC("fexit/XXX")
int BPF_PROG(fexit_XXX)
{
	struct bpf_perf_event_value *diff_val, *accum_val;
	__u32 filter_key, zero = 0;
	__u32 accum_key;
	struct bperf_filter_value *fval;

	if (!enabled)
		return 0;

	switch (type) {
	case BPERF_FILTER_GLOBAL:
		accum_key = zero;
		goto do_add;
	case BPERF_FILTER_CPU:
		filter_key = bpf_get_smp_processor_id();
		break;
	case BPERF_FILTER_PID:
		filter_key = bpf_get_current_pid_tgid() & 0xffffffff;
		break;
	case BPERF_FILTER_TGID:
		/* Use pid as the filter_key to exclude new task counts
		 * when inherit is disabled. Don't worry about the existing
		 * children in TGID losing their counts, bpf_counter has
		 * already added them to the filter map via perf_thread_map
		 * before this bpf prog runs.
		 */
		filter_key = inherit ?
			     bpf_get_current_pid_tgid() >> 32 :
			     bpf_get_current_pid_tgid() & 0xffffffff;
		break;
	default:
		return 0;
	}

	fval = bpf_map_lookup_elem(&filter, &filter_key);
	if (!fval)
		return 0;

	accum_key = fval->accum_key;
	if (fval->exited)
		bpf_map_delete_elem(&filter, &filter_key);

do_add:
	diff_val = bpf_map_lookup_elem(&diff_readings, &zero);
	if (!diff_val)
		return 0;

	accum_val = bpf_map_lookup_elem(&accum_readings, &accum_key);
	if (!accum_val)
		return 0;

	accum_val->counter += diff_val->counter;
	accum_val->enabled += diff_val->enabled;
	accum_val->running += diff_val->running;

	return 0;
}

/* The program is only used for PID or TGID filter types. */
SEC("tp_btf/task_newtask")
int BPF_PROG(on_newtask, struct task_struct *task, __u64 clone_flags)
{
	__u32 parent_key, child_key;
	struct bperf_filter_value *parent_fval;
	struct bperf_filter_value child_fval = { 0 };

	if (!enabled)
		return 0;

	switch (type) {
	case BPERF_FILTER_PID:
		parent_key = bpf_get_current_pid_tgid() & 0xffffffff;
		child_key = task->pid;
		break;
	case BPERF_FILTER_TGID:
		parent_key = bpf_get_current_pid_tgid() >> 32;
		child_key = task->tgid;
		if (child_key == parent_key)
			return 0;
		break;
	default:
		return 0;
	}

	/* Check if the current task is one of the target tasks to be counted */
	parent_fval = bpf_map_lookup_elem(&filter, &parent_key);
	if (!parent_fval)
		return 0;

	/* Start counting for the new task by adding it into filter map,
	 * inherit the accum key of its parent task so that they can be
	 * counted together.
	 */
	child_fval.accum_key = parent_fval->accum_key;
	child_fval.exited = 0;
	bpf_map_update_elem(&filter, &child_key, &child_fval, BPF_NOEXIST);

	return 0;
}

/* The program is only used for PID or TGID filter types. */
SEC("tp_btf/sched_process_exit")
int BPF_PROG(on_exittask, struct task_struct *task)
{
	__u32 pid;
	struct bperf_filter_value *fval;

	if (!enabled)
		return 0;

	/* Stop counting for this task by removing it from filter map.
	 * For TGID type, if the pid can be found in the map, it means that
	 * this pid belongs to the leader task. After the task exits, the
	 * tgid of its child tasks (if any) will be 1, so the pid can be
	 * safely removed.
	 */
	pid = task->pid;
	fval = bpf_map_lookup_elem(&filter, &pid);
	if (fval)
		fval->exited = 1;

	return 0;
}

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