// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
 * Copyright (c) 2023 David Vernet <dvernet@meta.com>
 * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
 */

#include <scx/common.bpf.h>

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

UEI_DEFINE(uei);

s32 BPF_STRUCT_OPS(enq_select_cpu_select_cpu, struct task_struct *p,
                   s32 prev_cpu, u64 wake_flags)
{
        /* Bounce all tasks to ops.enqueue() */
        return prev_cpu;
}

void BPF_STRUCT_OPS(enq_select_cpu_enqueue, struct task_struct *p,
                    u64 enq_flags)
{
        s32 cpu, prev_cpu = scx_bpf_task_cpu(p);
        bool found = false;

        cpu = scx_bpf_select_cpu_dfl(p, prev_cpu, 0, &found);
        if (found) {
                scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL_ON | cpu, SCX_SLICE_DFL, enq_flags);
                return;
        }

        scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
}

void BPF_STRUCT_OPS(enq_select_cpu_exit, struct scx_exit_info *ei)
{
        UEI_RECORD(uei, ei);
}

struct task_cpu_arg {
        pid_t pid;
};

SEC("syscall")
int select_cpu_from_user(struct task_cpu_arg *input)
{
        struct task_struct *p;
        bool found = false;
        s32 cpu;

        p = bpf_task_from_pid(input->pid);
        if (!p)
                return -EINVAL;

        bpf_rcu_read_lock();
        cpu = scx_bpf_select_cpu_dfl(p, bpf_get_smp_processor_id(), 0, &found);
        if (!found)
                cpu = -EBUSY;
        bpf_rcu_read_unlock();

        bpf_task_release(p);

        return cpu;
}

SEC(".struct_ops.link")
struct sched_ext_ops enq_select_cpu_ops = {
        .select_cpu             = (void *)enq_select_cpu_select_cpu,
        .enqueue                = (void *)enq_select_cpu_enqueue,
        .exit                   = (void *)enq_select_cpu_exit,
        .name                   = "enq_select_cpu",
        .timeout_ms             = 1000U,
};