1 files changed, 228 insertions, 0 deletions
diff --git a/fs/eventfd.c b/fs/eventfd.c
new file mode 100644
index 0000000..480e2b3
--- /dev/null
+++ b/fs/eventfd.c
@@ -0,0 +1,228 @@
+/*
+ *  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 {
+	spinlock_t lock;
+	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->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->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->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->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->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->lock);
+			schedule();
+			spin_lock_irq(&ctx->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->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->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->lock);
+			schedule();
+			spin_lock_irq(&ctx->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->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);
+	spin_lock_init(&ctx->lock);
+	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;
+}
+