/*
 *  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;
}