/* Kernel thread helper functions.
 *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
 *
 * Creation is done via keventd, 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 <asm/semaphore.h>

/*
 * We dont want to execute off keventd since it might
 * hold a semaphore our callers hold too:
 */
static struct workqueue_struct *helper_wq;

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

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

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 DECLARE_MUTEX(kthread_stop_lock);
static struct kthread_stop_info kthread_stop_info;

int kthread_should_stop(void)
{
        return (kthread_stop_info.k == current);
}
EXPORT_SYMBOL(kthread_should_stop);

static void kthread_exit_files(void)
{
        struct fs_struct *fs;
        struct task_struct *tsk = current;

        exit_fs(tsk);           /* current->fs->count--; */
        fs = init_task.fs;
        tsk->fs = fs;
        atomic_inc(&fs->count);
        exit_files(tsk);
        current->files = init_task.files;
        atomic_inc(&tsk->files->count);
}

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

        kthread_exit_files();

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

        /* Block and flush all signals (in case we're not from keventd). */
        sigfillset(&blocked);
        sigprocmask(SIG_BLOCK, &blocked, NULL);
        flush_signals(current);

        /* By default we can run anywhere, unlike keventd. */
        set_cpus_allowed(current, CPU_MASK_ALL);

        /* OK, tell user we're spawned, wait for stop or wakeup */
        __set_current_state(TASK_INTERRUPTIBLE);
        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;
}

/* We are keventd: create a thread. */
static void keventd_create_kthread(void *_create)
{
        struct kthread_create_info *create = _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 {
                wait_for_completion(&create->started);
                create->result = find_task_by_pid(pid);
        }
        complete(&create->done);
}

struct task_struct *kthread_create(int (*threadfn)(void *data),
                                   void *data,
                                   const char namefmt[],
                                   ...)
{
        struct kthread_create_info create;
        DECLARE_WORK(work, keventd_create_kthread, &create);

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

        /*
         * The workqueue needs to start up first:
         */
        if (!helper_wq)
                work.func(work.data);
        else {
                queue_work(helper_wq, &work);
                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);

void kthread_bind(struct task_struct *k, unsigned int cpu)
{
        BUG_ON(k->state != TASK_INTERRUPTIBLE);
        /* 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);

int kthread_stop(struct task_struct *k)
{
        int ret;

        down(&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);
        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;
        up(&kthread_stop_lock);

        return ret;
}
EXPORT_SYMBOL(kthread_stop);

static __init int helper_init(void)
{
        helper_wq = create_singlethread_workqueue("kthread");
        BUG_ON(!helper_wq);

        return 0;
}
core_initcall(helper_init);