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/*

 *  fs/timerfd.c

 *

 *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>

 *

 *

 *  Thanks to Thomas Gleixner for code reviews and useful comments.

 *

 */

#include <linux/file.h>

#include <linux/poll.h>

#include <linux/init.h>

#include <linux/fs.h>

#include <linux/sched.h>

#include <linux/kernel.h>

#include <linux/list.h>

#include <linux/spinlock.h>

#include <linux/time.h>

#include <linux/hrtimer.h>

#include <linux/anon_inodes.h>

#include <linux/timerfd.h>

struct timerfd_ctx {

        struct hrtimer tmr;

        ktime_t tintv;

        wait_queue_head_t wqh;

        int expired;

};

/*

 * This gets called when the timer event triggers. We set the "expired"

 * flag, but we do not re-arm the timer (in case it's necessary,

 * tintv.tv64 != 0) until the timer is read.

 */

static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)

{

        struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);

        unsigned long flags;

        spin_lock_irqsave(&ctx->wqh.lock, flags);

        ctx->expired = 1;

        wake_up_locked(&ctx->wqh);

        spin_unlock_irqrestore(&ctx->wqh.lock, flags);

        return HRTIMER_NORESTART;

}

static void timerfd_setup(struct timerfd_ctx *ctx, int clockid, int flags,

                          const struct itimerspec *ktmr)

{

        enum hrtimer_mode htmode;

        ktime_t texp;

        htmode = (flags & TFD_TIMER_ABSTIME) ?

                HRTIMER_MODE_ABS: HRTIMER_MODE_REL;

        texp = timespec_to_ktime(ktmr->it_value);

        ctx->expired = 0;

        ctx->tintv = timespec_to_ktime(ktmr->it_interval);

        hrtimer_init(&ctx->tmr, clockid, htmode);

        ctx->tmr.expires = texp;

        ctx->tmr.function = timerfd_tmrproc;

        if (texp.tv64 != 0)

                hrtimer_start(&ctx->tmr, texp, htmode);

}

static int timerfd_release(struct inode *inode, struct file *file)

{

        struct timerfd_ctx *ctx = file->private_data;

        hrtimer_cancel(&ctx->tmr);

        kfree(ctx);

        return 0;

}

static unsigned int timerfd_poll(struct file *file, poll_table *wait)

{

        struct timerfd_ctx *ctx = file->private_data;

        unsigned int events = 0;

        unsigned long flags;

        poll_wait(file, &ctx->wqh, wait);

        spin_lock_irqsave(&ctx->wqh.lock, flags);

        if (ctx->expired)

                events |= POLLIN;

        spin_unlock_irqrestore(&ctx->wqh.lock, flags);

        return events;

}

static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,

                            loff_t *ppos)

{

        struct timerfd_ctx *ctx = file->private_data;

        ssize_t res;

        u64 ticks = 0;

        DECLARE_WAITQUEUE(wait, current);

        if (count < sizeof(ticks))

                return -EINVAL;

        spin_lock_irq(&ctx->wqh.lock);

        res = -EAGAIN;

        if (!ctx->expired && !(file->f_flags & O_NONBLOCK)) {

                __add_wait_queue(&ctx->wqh, &wait);

                for (res = 0;;) {

                        set_current_state(TASK_INTERRUPTIBLE);

                        if (ctx->expired) {

                                res = 0;

                                break;

                        }

                        if (signal_pending(current)) {

                                res = -ERESTARTSYS;

                                break;

                        }

                        spin_unlock_irq(&ctx->wqh.lock);

                        schedule();

                        spin_lock_irq(&ctx->wqh.lock);

                }

                __remove_wait_queue(&ctx->wqh, &wait);

                __set_current_state(TASK_RUNNING);

        }

        if (ctx->expired) {

                ctx->expired = 0;

                if (ctx->tintv.tv64 != 0) {

                        /*

                         * If tintv.tv64 != 0, this is a periodic timer that

                         * needs to be re-armed. We avoid doing it in the timer

                         * callback to avoid DoS attacks specifying a very

                         * short timer period.

                         */

                        ticks = (u64)

                                hrtimer_forward(&ctx->tmr,

                                                hrtimer_cb_get_time(&ctx->tmr),

                                                ctx->tintv);

                        hrtimer_restart(&ctx->tmr);

                } else

                        ticks = 1;

        }

        spin_unlock_irq(&ctx->wqh.lock);

        if (ticks)

                res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);

        return res;

}

static const struct file_operations timerfd_fops = {

        .release        = timerfd_release,

        .poll           = timerfd_poll,

        .read           = timerfd_read,

};

asmlinkage long sys_timerfd(int ufd, int clockid, int flags,

                            const struct itimerspec __user *utmr)

{

        int error;

        struct timerfd_ctx *ctx;

        struct file *file;

        struct inode *inode;

        struct itimerspec ktmr;

        if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))

                return -EFAULT;

        if (clockid != CLOCK_MONOTONIC &&

            clockid != CLOCK_REALTIME)

                return -EINVAL;

        if (!timespec_valid(&ktmr.it_value) ||

            !timespec_valid(&ktmr.it_interval))

                return -EINVAL;

        if (ufd == -1) {

                ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);

                if (!ctx)

                        return -ENOMEM;

                init_waitqueue_head(&ctx->wqh);

                timerfd_setup(ctx, clockid, flags, &ktmr);

                /*

                 * When we call this, the initialization must be complete, since

                 * anon_inode_getfd() will install the fd.

                 */

                error = anon_inode_getfd(&ufd, &inode, &file, "[timerfd]",

                                         &timerfd_fops, ctx);

                if (error)

                        goto err_tmrcancel;

        } else {

                file = fget(ufd);

                if (!file)

                        return -EBADF;

                ctx = file->private_data;

                if (file->f_op != &timerfd_fops) {

                        fput(file);

                        return -EINVAL;

                }

                /*

                 * We need to stop the existing timer before reprogramming

                 * it to the new values.

                 */

                for (;;) {

                        spin_lock_irq(&ctx->wqh.lock);

                        if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)

                                break;

                        spin_unlock_irq(&ctx->wqh.lock);

                        cpu_relax();

                }

                /*

                 * Re-program the timer to the new value ...

                 */

                timerfd_setup(ctx, clockid, flags, &ktmr);

                spin_unlock_irq(&ctx->wqh.lock);

                fput(file);

        }

        return ufd;

err_tmrcancel:

        hrtimer_cancel(&ctx->tmr);

        kfree(ctx);

        return error;

}