root/fs/eventfd.c

DEFINITIONS

1. eventfd_signal
2. eventfd_release
3. eventfd_poll
4. eventfd_read
5. eventfd_write
6. eventfd_fget
7. sys_eventfd2
8. sys_eventfd

/*
 *  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>
#include <linux/syscalls.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_eventfd2(unsigned int count, int flags)
{
        int fd;
        struct eventfd_ctx *ctx;

        /* Check the EFD_* constants for consistency.  */
        BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
        BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);

        if (flags & ~(EFD_CLOEXEC | EFD_NONBLOCK))
                return -EINVAL;

        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.
         */
        fd = anon_inode_getfd("[eventfd]", &eventfd_fops, ctx,
                              flags & (O_CLOEXEC | O_NONBLOCK));
        if (fd < 0)
                kfree(ctx);
        return fd;
}

asmlinkage long sys_eventfd(unsigned int count)
{
        return sys_eventfd2(count, 0);
}