/*
 *  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/slab.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>
#include <linux/syscalls.h>
#include <linux/rcupdate.h>

struct timerfd_ctx {
        struct hrtimer tmr;
        ktime_t tintv;
        ktime_t moffs;
        wait_queue_head_t wqh;
        u64 ticks;
        int expired;
        int clockid;
        struct rcu_head rcu;
        struct list_head clist;
        bool might_cancel;
};

static LIST_HEAD(cancel_list);
static DEFINE_SPINLOCK(cancel_lock);

/*
 * 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 accessed.
 */
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;
        ctx->ticks++;
        wake_up_locked(&ctx->wqh);
        spin_unlock_irqrestore(&ctx->wqh.lock, flags);

        return HRTIMER_NORESTART;
}

/*
 * Called when the clock was set to cancel the timers in the cancel
 * list. This will wake up processes waiting on these timers. The
 * wake-up requires ctx->ticks to be non zero, therefore we increment
 * it before calling wake_up_locked().
 */
void timerfd_clock_was_set(void)
{
        ktime_t moffs = ktime_get_monotonic_offset();
        struct timerfd_ctx *ctx;
        unsigned long flags;

        rcu_read_lock();
        list_for_each_entry_rcu(ctx, &cancel_list, clist) {
                if (!ctx->might_cancel)
                        continue;
                spin_lock_irqsave(&ctx->wqh.lock, flags);
                if (ctx->moffs.tv64 != moffs.tv64) {
                        ctx->moffs.tv64 = KTIME_MAX;
                        ctx->ticks++;
                        wake_up_locked(&ctx->wqh);
                }
                spin_unlock_irqrestore(&ctx->wqh.lock, flags);
        }
        rcu_read_unlock();
}

static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
        if (ctx->might_cancel) {
                ctx->might_cancel = false;
                spin_lock(&cancel_lock);
                list_del_rcu(&ctx->clist);
                spin_unlock(&cancel_lock);
        }
}

static bool timerfd_canceled(struct timerfd_ctx *ctx)
{
        if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
                return false;
        ctx->moffs = ktime_get_monotonic_offset();
        return true;
}

static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
{
        if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) &&
            (flags & TFD_TIMER_CANCEL_ON_SET)) {
                if (!ctx->might_cancel) {
                        ctx->might_cancel = true;
                        spin_lock(&cancel_lock);
                        list_add_rcu(&ctx->clist, &cancel_list);
                        spin_unlock(&cancel_lock);
                }
        } else if (ctx->might_cancel) {
                timerfd_remove_cancel(ctx);
        }
}

static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
{
        ktime_t remaining;

        remaining = hrtimer_expires_remaining(&ctx->tmr);
        return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
}

static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
                         const struct itimerspec *ktmr)
{
        enum hrtimer_mode htmode;
        ktime_t texp;
        int clockid = ctx->clockid;

        htmode = (flags & TFD_TIMER_ABSTIME) ?
                HRTIMER_MODE_ABS: HRTIMER_MODE_REL;

        texp = timespec_to_ktime(ktmr->it_value);
        ctx->expired = 0;
        ctx->ticks = 0;
        ctx->tintv = timespec_to_ktime(ktmr->it_interval);
        hrtimer_init(&ctx->tmr, clockid, htmode);
        hrtimer_set_expires(&ctx->tmr, texp);
        ctx->tmr.function = timerfd_tmrproc;
        if (texp.tv64 != 0) {
                hrtimer_start(&ctx->tmr, texp, htmode);
                if (timerfd_canceled(ctx))
                        return -ECANCELED;
        }
        return 0;
}

static int timerfd_release(struct inode *inode, struct file *file)
{
        struct timerfd_ctx *ctx = file->private_data;

        timerfd_remove_cancel(ctx);
        hrtimer_cancel(&ctx->tmr);
        kfree_rcu(ctx, rcu);
        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->ticks)
                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;

        if (count < sizeof(ticks))
                return -EINVAL;
        spin_lock_irq(&ctx->wqh.lock);
        if (file->f_flags & O_NONBLOCK)
                res = -EAGAIN;
        else
                res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);

        /*
         * If clock has changed, we do not care about the
         * ticks and we do not rearm the timer. Userspace must
         * reevaluate anyway.
         */
        if (timerfd_canceled(ctx)) {
                ctx->ticks = 0;
                ctx->expired = 0;
                res = -ECANCELED;
        }

        if (ctx->ticks) {
                ticks = ctx->ticks;

                if (ctx->expired && ctx->tintv.tv64) {
                        /*
                         * 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 += hrtimer_forward_now(&ctx->tmr,
                                                     ctx->tintv) - 1;
                        hrtimer_restart(&ctx->tmr);
                }
                ctx->expired = 0;
                ctx->ticks = 0;
        }
        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,
        .llseek         = noop_llseek,
};

static struct file *timerfd_fget(int fd)
{
        struct file *file;

        file = fget(fd);
        if (!file)
                return ERR_PTR(-EBADF);
        if (file->f_op != &timerfd_fops) {
                fput(file);
                return ERR_PTR(-EINVAL);
        }

        return file;
}

SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
{
        int ufd;
        struct timerfd_ctx *ctx;

        /* Check the TFD_* constants for consistency.  */
        BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
        BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);

        if ((flags & ~TFD_CREATE_FLAGS) ||
            (clockid != CLOCK_MONOTONIC &&
             clockid != CLOCK_REALTIME))
                return -EINVAL;

        ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
        if (!ctx)
                return -ENOMEM;

        init_waitqueue_head(&ctx->wqh);
        ctx->clockid = clockid;
        hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
        ctx->moffs = ktime_get_monotonic_offset();

        ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
                               O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
        if (ufd < 0)
                kfree(ctx);

        return ufd;
}

SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
                const struct itimerspec __user *, utmr,
                struct itimerspec __user *, otmr)
{
        struct file *file;
        struct timerfd_ctx *ctx;
        struct itimerspec ktmr, kotmr;
        int ret;

        if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
                return -EFAULT;

        if ((flags & ~TFD_SETTIME_FLAGS) ||
            !timespec_valid(&ktmr.it_value) ||
            !timespec_valid(&ktmr.it_interval))
                return -EINVAL;

        file = timerfd_fget(ufd);
        if (IS_ERR(file))
                return PTR_ERR(file);
        ctx = file->private_data;

        timerfd_setup_cancel(ctx, flags);

        /*
         * 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();
        }

        /*
         * If the timer is expired and it's periodic, we need to advance it
         * because the caller may want to know the previous expiration time.
         * We do not update "ticks" and "expired" since the timer will be
         * re-programmed again in the following timerfd_setup() call.
         */
        if (ctx->expired && ctx->tintv.tv64)
                hrtimer_forward_now(&ctx->tmr, ctx->tintv);

        kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
        kotmr.it_interval = ktime_to_timespec(ctx->tintv);

        /*
         * Re-program the timer to the new value ...
         */
        ret = timerfd_setup(ctx, flags, &ktmr);

        spin_unlock_irq(&ctx->wqh.lock);
        fput(file);
        if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
                return -EFAULT;

        return ret;
}

SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
{
        struct file *file;
        struct timerfd_ctx *ctx;
        struct itimerspec kotmr;

        file = timerfd_fget(ufd);
        if (IS_ERR(file))
                return PTR_ERR(file);
        ctx = file->private_data;

        spin_lock_irq(&ctx->wqh.lock);
        if (ctx->expired && ctx->tintv.tv64) {
                ctx->expired = 0;
                ctx->ticks +=
                        hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
                hrtimer_restart(&ctx->tmr);
        }
        kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
        kotmr.it_interval = ktime_to_timespec(ctx->tintv);
        spin_unlock_irq(&ctx->wqh.lock);
        fput(file);

        return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
}