/* Kernel thread helper functions.
 *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
 *
 * Creation is done via kthreadd, so that we get a clean environment
 * even if we're invoked from userspace (think modprobe, hotplug cpu,
 * etc.).
 */
#include <linux/sched.h>
#include <linux/kthread.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/unistd.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <asm/semaphore.h>

#define KTHREAD_NICE_LEVEL (-5)

static DEFINE_SPINLOCK(kthread_create_lock);
static LIST_HEAD(kthread_create_list);
struct task_struct *kthreadd_task;

struct kthread_create_info
{
        /* Information passed to kthread() from kthreadd. */
        int (*threadfn)(void *data);
        void *data;
        struct completion started;

        /* Result passed back to kthread_create() from kthreadd. */
        struct task_struct *result;
        struct completion done;

        struct list_head list;
};

struct kthread_stop_info
{
        struct task_struct *k;
        int err;
        struct completion done;
};

/* Thread stopping is done by setthing this var: lock serializes
 * multiple kthread_stop calls. */
static DEFINE_MUTEX(kthread_stop_lock);
static struct kthread_stop_info kthread_stop_info;

/**
 * kthread_should_stop - should this kthread return now?
 *
 * When someone calls kthread_stop() on your kthread, it will be woken
 * and this will return true.  You should then return, and your return
 * value will be passed through to kthread_stop().
 */
int kthread_should_stop(void)
{
        return (kthread_stop_info.k == current);
}
EXPORT_SYMBOL(kthread_should_stop);

static int kthread(void *_create)
{
        struct kthread_create_info *create = _create;
        int (*threadfn)(void *data);
        void *data;
        int ret = -EINTR;

        /* Copy data: it's on kthread's stack */
        threadfn = create->threadfn;
        data = create->data;

        /* OK, tell user we're spawned, wait for stop or wakeup */
        __set_current_state(TASK_UNINTERRUPTIBLE);
        complete(&create->started);
        schedule();

        if (!kthread_should_stop())
                ret = threadfn(data);

        /* It might have exited on its own, w/o kthread_stop.  Check. */
        if (kthread_should_stop()) {
                kthread_stop_info.err = ret;
                complete(&kthread_stop_info.done);
        }
        return 0;
}

static void create_kthread(struct kthread_create_info *create)
{
        int pid;

        /* We want our own signal handler (we take no signals by default). */
        pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
        if (pid < 0) {
                create->result = ERR_PTR(pid);
        } else {
                struct sched_param param = { .sched_priority = 0 };
                wait_for_completion(&create->started);
                read_lock(&tasklist_lock);
                create->result = find_task_by_pid(pid);
                read_unlock(&tasklist_lock);
                /*
                 * root may have changed our (kthreadd's) priority or CPU mask.
                 * The kernel thread should not inherit these properties.
                 */
                sched_setscheduler(create->result, SCHED_NORMAL, &param);
                set_user_nice(create->result, KTHREAD_NICE_LEVEL);
                set_cpus_allowed(create->result, CPU_MASK_ALL);
        }
        complete(&create->done);
}

/**
 * kthread_create - create a kthread.
 * @threadfn: the function to run until signal_pending(current).
 * @data: data ptr for @threadfn.
 * @namefmt: printf-style name for the thread.
 *
 * Description: This helper function creates and names a kernel
 * thread.  The thread will be stopped: use wake_up_process() to start
 * it.  See also kthread_run(), kthread_create_on_cpu().
 *
 * When woken, the thread will run @threadfn() with @data as its
 * argument. @threadfn() can either call do_exit() directly if it is a
 * standalone thread for which noone will call kthread_stop(), or
 * return when 'kthread_should_stop()' is true (which means
 * kthread_stop() has been called).  The return value should be zero
 * or a negative error number; it will be passed to kthread_stop().
 *
 * Returns a task_struct or ERR_PTR(-ENOMEM).
 */
struct task_struct *kthread_create(int (*threadfn)(void *data),
                                   void *data,
                                   const char namefmt[],
                                   ...)
{
        struct kthread_create_info create;

        create.threadfn = threadfn;
        create.data = data;
        init_completion(&create.started);
        init_completion(&create.done);

        spin_lock(&kthread_create_lock);
        list_add_tail(&create.list, &kthread_create_list);
        wake_up_process(kthreadd_task);
        spin_unlock(&kthread_create_lock);

        wait_for_completion(&create.done);

        if (!IS_ERR(create.result)) {
                va_list args;
                va_start(args, namefmt);
                vsnprintf(create.result->comm, sizeof(create.result->comm),
                          namefmt, args);
                va_end(args);
        }
        return create.result;
}
EXPORT_SYMBOL(kthread_create);

/**
 * kthread_bind - bind a just-created kthread to a cpu.
 * @k: thread created by kthread_create().
 * @cpu: cpu (might not be online, must be possible) for @k to run on.
 *
 * Description: This function is equivalent to set_cpus_allowed(),
 * except that @cpu doesn't need to be online, and the thread must be
 * stopped (i.e., just returned from kthread_create()).
 */
void kthread_bind(struct task_struct *k, unsigned int cpu)
{
        if (k->state != TASK_UNINTERRUPTIBLE) {
                WARN_ON(1);
                return;
        }
        /* Must have done schedule() in kthread() before we set_task_cpu */
        wait_task_inactive(k);
        set_task_cpu(k, cpu);
        k->cpus_allowed = cpumask_of_cpu(cpu);
}
EXPORT_SYMBOL(kthread_bind);

/**
 * kthread_stop - stop a thread created by kthread_create().
 * @k: thread created by kthread_create().
 *
 * Sets kthread_should_stop() for @k to return true, wakes it, and
 * waits for it to exit.  Your threadfn() must not call do_exit()
 * itself if you use this function!  This can also be called after
 * kthread_create() instead of calling wake_up_process(): the thread
 * will exit without calling threadfn().
 *
 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 * was never called.
 */
int kthread_stop(struct task_struct *k)
{
        int ret;

        mutex_lock(&kthread_stop_lock);

        /* It could exit after stop_info.k set, but before wake_up_process. */
        get_task_struct(k);

        /* Must init completion *before* thread sees kthread_stop_info.k */
        init_completion(&kthread_stop_info.done);
        smp_wmb();

        /* Now set kthread_should_stop() to true, and wake it up. */
        kthread_stop_info.k = k;
        wake_up_process(k);
        put_task_struct(k);

        /* Once it dies, reset stop ptr, gather result and we're done. */
        wait_for_completion(&kthread_stop_info.done);
        kthread_stop_info.k = NULL;
        ret = kthread_stop_info.err;
        mutex_unlock(&kthread_stop_lock);

        return ret;
}
EXPORT_SYMBOL(kthread_stop);

int kthreadd(void *unused)
{
        struct task_struct *tsk = current;

        /* Setup a clean context for our children to inherit. */
        set_task_comm(tsk, "kthreadd");
        ignore_signals(tsk);
        set_user_nice(tsk, KTHREAD_NICE_LEVEL);
        set_cpus_allowed(tsk, CPU_MASK_ALL);

        current->flags |= PF_NOFREEZE;

        for (;;) {
                set_current_state(TASK_INTERRUPTIBLE);
                if (list_empty(&kthread_create_list))
                        schedule();
                __set_current_state(TASK_RUNNING);

                spin_lock(&kthread_create_lock);
                while (!list_empty(&kthread_create_list)) {
                        struct kthread_create_info *create;

                        create = list_entry(kthread_create_list.next,
                                            struct kthread_create_info, list);
                        list_del_init(&create->list);
                        spin_unlock(&kthread_create_lock);

                        create_kthread(create);

                        spin_lock(&kthread_create_lock);
                }
                spin_unlock(&kthread_create_lock);
        }

        return 0;
}