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/*

 *  fs/eventfd.c

 *

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

 *

 */

#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/anon_inodes.h>

#include <linux/eventfd.h>

struct eventfd_ctx {

        wait_queue_head_t wqh;

        /*

         * Every time that a write(2) is performed on an eventfd, the

         * value of the __u64 being written is added to "count" and a

         * wakeup is performed on "wqh". A read(2) will return the "count"

         * value to userspace, and will reset "count" to zero. The kernel

         * size eventfd_signal() also, adds to the "count" counter and

         * issue a wakeup.

         */

        __u64 count;

};

/*

 * Adds "n" to the eventfd counter "count". Returns "n" in case of

 * success, or a value lower then "n" in case of coutner overflow.

 * This function is supposed to be called by the kernel in paths

 * that do not allow sleeping. In this function we allow the counter

 * to reach the ULLONG_MAX value, and we signal this as overflow

 * condition by returining a POLLERR to poll(2).

 */

int eventfd_signal(struct file *file, int n)

{

        struct eventfd_ctx *ctx = file->private_data;

        unsigned long flags;

        if (n < 0)

                return -EINVAL;

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

        if (ULLONG_MAX - ctx->count < n)

                n = (int) (ULLONG_MAX - ctx->count);

        ctx->count += n;

        if (waitqueue_active(&ctx->wqh))

                wake_up_locked(&ctx->wqh);

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

        return n;

}

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

{

        kfree(file->private_data);

        return 0;

}

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

{

        struct eventfd_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->count > 0)

                events |= POLLIN;

        if (ctx->count == ULLONG_MAX)

                events |= POLLERR;

        if (ULLONG_MAX - 1 > ctx->count)

                events |= POLLOUT;

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

        return events;

}

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

                            loff_t *ppos)

{

        struct eventfd_ctx *ctx = file->private_data;

        ssize_t res;

        __u64 ucnt;

        DECLARE_WAITQUEUE(wait, current);

        if (count < sizeof(ucnt))

                return -EINVAL;

        spin_lock_irq(&ctx->wqh.lock);

        res = -EAGAIN;

        ucnt = ctx->count;

        if (ucnt > 0)

                res = sizeof(ucnt);

        else if (!(file->f_flags & O_NONBLOCK)) {

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

                for (res = 0;;) {

                        set_current_state(TASK_INTERRUPTIBLE);

                        if (ctx->count > 0) {

                                ucnt = ctx->count;

                                res = sizeof(ucnt);

                                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 (res > 0) {

                ctx->count = 0;

                if (waitqueue_active(&ctx->wqh))

                        wake_up_locked(&ctx->wqh);

        }

        spin_unlock_irq(&ctx->wqh.lock);

        if (res > 0 && put_user(ucnt, (__u64 __user *) buf))

                return -EFAULT;

        return res;

}

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

                             loff_t *ppos)

{

        struct eventfd_ctx *ctx = file->private_data;

        ssize_t res;

        __u64 ucnt;

        DECLARE_WAITQUEUE(wait, current);

        if (count < sizeof(ucnt))

                return -EINVAL;

        if (copy_from_user(&ucnt, buf, sizeof(ucnt)))

                return -EFAULT;

        if (ucnt == ULLONG_MAX)

                return -EINVAL;

        spin_lock_irq(&ctx->wqh.lock);

        res = -EAGAIN;

        if (ULLONG_MAX - ctx->count > ucnt)

                res = sizeof(ucnt);

        else if (!(file->f_flags & O_NONBLOCK)) {

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

                for (res = 0;;) {

                        set_current_state(TASK_INTERRUPTIBLE);

                        if (ULLONG_MAX - ctx->count > ucnt) {

                                res = sizeof(ucnt);

                                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 (res > 0) {

                ctx->count += ucnt;

                if (waitqueue_active(&ctx->wqh))

                        wake_up_locked(&ctx->wqh);

        }

        spin_unlock_irq(&ctx->wqh.lock);

        return res;

}

static const struct file_operations eventfd_fops = {

        .release        = eventfd_release,

        .poll           = eventfd_poll,

        .read           = eventfd_read,

        .write          = eventfd_write,

};

struct file *eventfd_fget(int fd)

{

        struct file *file;

        file = fget(fd);

        if (!file)

                return ERR_PTR(-EBADF);

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

                fput(file);

                return ERR_PTR(-EINVAL);

        }

        return file;

}

asmlinkage long sys_eventfd(unsigned int count)

{

        int error, fd;

        struct eventfd_ctx *ctx;

        struct file *file;

        struct inode *inode;

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

        if (!ctx)

                return -ENOMEM;

        init_waitqueue_head(&ctx->wqh);

        ctx->count = count;

        /*

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

         * anon_inode_getfd() will install the fd.

         */

        error = anon_inode_getfd(&fd, &inode, &file, "[eventfd]",

                                 &eventfd_fops, ctx);

        if (!error)

                return fd;

        kfree(ctx);

        return error;

}