uhid.c

/*
 * User-space I/O driver support for HID subsystem
 * Copyright (c) 2012 David Herrmann
 */

/*
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 */

#include <linux/atomic.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/hid.h>
#include <linux/input.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/poll.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/uhid.h>
#include <linux/wait.h>

#define UHID_NAME	"uhid"
#define UHID_BUFSIZE	32

struct uhid_device {
	struct mutex devlock;
	struct hid_device *hid;

	wait_queue_head_t waitq;
	spinlock_t qlock;
	__u8 head;
	__u8 tail;
	struct uhid_event *outq[UHID_BUFSIZE];
};

static struct miscdevice uhid_misc;

static void uhid_queue(struct uhid_device *uhid, struct uhid_event *ev)
{
	__u8 newhead;

	newhead = (uhid->head + 1) % UHID_BUFSIZE;

	if (newhead != uhid->tail) {
		uhid->outq[uhid->head] = ev;
		uhid->head = newhead;
		wake_up_interruptible(&uhid->waitq);
	} else {
		hid_warn(uhid->hid, "Output queue is full\n");
		kfree(ev);
	}
}

static int uhid_queue_event(struct uhid_device *uhid, __u32 event)
{
	unsigned long flags;
	struct uhid_event *ev;

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

	ev->type = event;

	spin_lock_irqsave(&uhid->qlock, flags);
	uhid_queue(uhid, ev);
	spin_unlock_irqrestore(&uhid->qlock, flags);

	return 0;
}

static int uhid_char_open(struct inode *inode, struct file *file)
{
	struct uhid_device *uhid;

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

	mutex_init(&uhid->devlock);
	spin_lock_init(&uhid->qlock);
	init_waitqueue_head(&uhid->waitq);

	file->private_data = uhid;
	nonseekable_open(inode, file);

	return 0;
}

static int uhid_char_release(struct inode *inode, struct file *file)
{
	struct uhid_device *uhid = file->private_data;
	unsigned int i;

	for (i = 0; i < UHID_BUFSIZE; ++i)
		kfree(uhid->outq[i]);

	kfree(uhid);

	return 0;
}

static ssize_t uhid_char_read(struct file *file, char __user *buffer,
				size_t count, loff_t *ppos)
{
	struct uhid_device *uhid = file->private_data;
	int ret;
	unsigned long flags;
	size_t len;

	/* they need at least the "type" member of uhid_event */
	if (count < sizeof(__u32))
		return -EINVAL;

try_again:
	if (file->f_flags & O_NONBLOCK) {
		if (uhid->head == uhid->tail)
			return -EAGAIN;
	} else {
		ret = wait_event_interruptible(uhid->waitq,
						uhid->head != uhid->tail);
		if (ret)
			return ret;
	}

	ret = mutex_lock_interruptible(&uhid->devlock);
	if (ret)
		return ret;

	if (uhid->head == uhid->tail) {
		mutex_unlock(&uhid->devlock);
		goto try_again;
	} else {
		len = min(count, sizeof(**uhid->outq));
		if (copy_to_user(buffer, &uhid->outq[uhid->tail], len)) {
			ret = -EFAULT;
		} else {
			kfree(uhid->outq[uhid->tail]);
			uhid->outq[uhid->tail] = NULL;

			spin_lock_irqsave(&uhid->qlock, flags);
			uhid->tail = (uhid->tail + 1) % UHID_BUFSIZE;
			spin_unlock_irqrestore(&uhid->qlock, flags);
		}
	}

	mutex_unlock(&uhid->devlock);
	return ret ? ret : len;
}

static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
				size_t count, loff_t *ppos)
{
	return 0;
}

static unsigned int uhid_char_poll(struct file *file, poll_table *wait)
{
	struct uhid_device *uhid = file->private_data;

	poll_wait(file, &uhid->waitq, wait);

	if (uhid->head != uhid->tail)
		return POLLIN | POLLRDNORM;

	return 0;
}

static const struct file_operations uhid_fops = {
	.owner		= THIS_MODULE,
	.open		= uhid_char_open,
	.release	= uhid_char_release,
	.read		= uhid_char_read,
	.write		= uhid_char_write,
	.poll		= uhid_char_poll,
	.llseek		= no_llseek,
};

static struct miscdevice uhid_misc = {
	.fops		= &uhid_fops,
	.minor		= MISC_DYNAMIC_MINOR,
	.name		= UHID_NAME,
};

static int __init uhid_init(void)
{
	return misc_register(&uhid_misc);
}

static void __exit uhid_exit(void)
{
	misc_deregister(&uhid_misc);
}

module_init(uhid_init);
module_exit(uhid_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("David Herrmann <dh.herrmann@gmail.com>");
MODULE_DESCRIPTION("User-space I/O driver support for HID subsystem");