[RFC,v3,1/1] Input: Add userio module
diff mbox

Message ID 1437594773-22274-2-git-send-email-cpaul@redhat.com
State Superseded
Headers show

Commit Message

cpaul@redhat.com July 22, 2015, 7:52 p.m. UTC
Debugging input devices, specifically laptop touchpads, can be tricky
without having the physical device handy. Here we try to remedy that
with userio. This module allows an application to connect to a character
device provided by the kernel, and emulate any serio device. In
combination with userspace programs that can record PS/2 devices and
replay them through the /dev/userio device, this allows developers to
debug driver issues on the PS/2 level with devices simply by requesting
a recording from the user experiencing the issue without having to have
the physical hardware in front of them.

Signed-off-by: Stephen Chandler Paul <cpaul@redhat.com>
---
 Documentation/input/userio.txt |  70 +++++++++++
 MAINTAINERS                    |   6 +
 drivers/input/serio/Kconfig    |  11 ++
 drivers/input/serio/Makefile   |   1 +
 drivers/input/serio/userio.c   | 261 +++++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/userio.h    |  42 +++++++
 6 files changed, 391 insertions(+)
 create mode 100644 Documentation/input/userio.txt
 create mode 100644 drivers/input/serio/userio.c
 create mode 100644 include/uapi/linux/userio.h

Comments

cpaul@redhat.com July 22, 2015, 8:16 p.m. UTC | #1
Forgot to add the changes I made onto here, whoops!

 * Allocate the serio struct separately, we don't have control over
   when it's freed
 * Use locking when working with the head or when working with the
   tail. Use two seperate locks so that we only risk making the
   userspace threads wait, not the kernel threads
 * Use modulus operations when incrementing the head and the tail
 * Check for read()s with length 0, return immediately if we find one
 * When doing ps2emu_device_write(), check to make sure that the ps2emu
   struct hasn't been set for destruction (being set to NULL), if it
   has just abort the write
 * Don't assign ps2emu to NULL, kzalloc will set it to NULL if
   allocation fails
 * Get rid of some ugly whitespace
 * Remove an unused include header
 * Allow any port types to be used
 * Rename the module from ps2emu to userio
 * Change documentation in Kconfig to say "using the userio kernel
   module" as opposed to "using the userio tools.", since it's possible
   there may be tools other then the ps2emu tools used with userio in
   the future.
 * Mention the requirement for <linux/serio.h>

On Wed, 2015-07-22 at 15:52 -0400, Stephen Chandler Paul wrote:
> Debugging input devices, specifically laptop touchpads, can be tricky
> without having the physical device handy. Here we try to remedy that
> with userio. This module allows an application to connect to a 
> character
> device provided by the kernel, and emulate any serio device. In
> combination with userspace programs that can record PS/2 devices and
> replay them through the /dev/userio device, this allows developers to
> debug driver issues on the PS/2 level with devices simply by 
> requesting
> a recording from the user experiencing the issue without having to 
> have
> the physical hardware in front of them.
> 
> Signed-off-by: Stephen Chandler Paul <cpaul@redhat.com>
> ---
>  Documentation/input/userio.txt |  70 +++++++++++
>  MAINTAINERS                    |   6 +
>  drivers/input/serio/Kconfig    |  11 ++
>  drivers/input/serio/Makefile   |   1 +
>  drivers/input/serio/userio.c   | 261 
> +++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/userio.h    |  42 +++++++
>  6 files changed, 391 insertions(+)
>  create mode 100644 Documentation/input/userio.txt
>  create mode 100644 drivers/input/serio/userio.c
>  create mode 100644 include/uapi/linux/userio.h
> 
> diff --git a/Documentation/input/userio.txt 
> b/Documentation/input/userio.txt
> new file mode 100644
> index 0000000..0880c0f
> --- /dev/null
> +++ b/Documentation/input/userio.txt
> @@ -0,0 +1,70 @@
> +			      The userio Protocol
> +	     (c) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
> +			      Sponsored by Red Hat
> +--------------------------------------------------------------------
> ------------
> +
> +1. Introduction
> +~~~~~~~~~~~~~~~
> +  This module is intended to try to make the lives of input driver 
> developers
> +easier by allowing them to test various serio devices (mainly the 
> various
> +touchpads found on laptops) without having to have the physical 
> device in front
> +of them. userio accomplishes this by allowing any privileged 
> userspace program
> +to directly interact with the kernel's serio driver and control a 
> virtual serio
> +port from there.
> +
> +2. Usage overview
> +~~~~~~~~~~~~~~~~~
> +  In order to interact with the userio kernel module, one simply 
> opens the
> +/dev/userio character device in their applications. Commands are 
> sent to the
> +kernel module by writing to the device, and any data received from 
> the serio
> +driver is read as-is from the /dev/userio device. All of the 
> structures and
> +macros you need to interact with the device are defined in 
> <linux/userio.h> and
> +<linux/serio.h>.
> +
> +3. Command Structure
> +~~~~~~~~~~~~~~~~~~~~
> +  The struct used for sending commands to /dev/userio is as follows:
> +
> +	struct userio_cmd {
> +		__u8 type;
> +		__u8 data;
> +	};
> +
> +  "type" describes the type of command that is being sent. This can 
> be any one
> +of the USERIO_CMD macros defined in <linux/userio.h>. "data" is the 
> argument
> +that goes along with the command. In the event that the command 
> doesn't have an
> +argument, this field can be left untouched and will be ignored by 
> the kernel.
> +Each command should be sent by writing the struct directly to the 
> character
> +device. In the event that the command you send is invalid, an error 
> will be
> +returned by the character device and a more descriptive error will 
> be printed
> +to the kernel log. Only one command can be sent at a time, any 
> additional data
> +written to the character device after the initial command will be 
> ignored.
> +  To close the virtual serio port, just close /dev/userio.
> +
> +4. Commands
> +~~~~~~~~~~~
> +
> +4.1 USERIO_CMD_REGISTER
> +~~~~~~~~~~~~~~~~~~~~~~~
> +  Registers the port with the serio driver and begins transmitting 
> data back and
> +forth. Registration can only be performed once a port type is set 
> with
> +USERIO_CMD_SET_PORT_TYPE. Has no argument.
> +
> +4.2 USERIO_CMD_SET_PORT_TYPE
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +  Sets the type of port we're emulating, where "data" is the port 
> type being
> +set. Can be any of the macros from <linux/serio.h>. For example: 
> SERIO_8042
> +would set the port type to be a normal PS/2 port.
> +
> +4.3 USERIO_CMD_SEND_INTERRUPT
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +  Sends an interrupt through the virtual serio port to the serio 
> driver, where
> +"data" is the interrupt data being sent.
> +
> +5. Userspace tools
> +~~~~~~~~~~~~~~~~~~
> +  The userio userspace tools are able to record PS/2 devices using 
> some of the
> +debugging information from i8042, and play back the devices on 
> /dev/userio. The
> +latest version of these tools can be found at:
> +
> +	https://github.com/Lyude/ps2emu
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a226416..68a0977 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10877,6 +10877,12 @@ S:	Maintained
>  F:	drivers/media/v4l2-core/videobuf2-*
>  F:	include/media/videobuf2-*
>  
> +VIRTUAL PS/2 DEVICE DRIVER
> +M:	Stephen Chandler Paul <thatslyude@gmail.com>
> +S:	Maintained
> +F:	drivers/input/serio/ps2emu.c
> +F:	include/uapi/linux/ps2emu.h
> +
>  VIRTIO CONSOLE DRIVER
>  M:	Amit Shah <amit.shah@redhat.com>
>  L:	virtualization@lists.linux-foundation.org
> diff --git a/drivers/input/serio/Kconfig 
> b/drivers/input/serio/Kconfig
> index 200841b..22b8b58 100644
> --- a/drivers/input/serio/Kconfig
> +++ b/drivers/input/serio/Kconfig
> @@ -292,4 +292,15 @@ config SERIO_SUN4I_PS2
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called sun4i-ps2.
>  
> +config USERIO
> +	tristate "Virtual serio device support"
> +	help
> +	  Say Y here if you want to emulate serio devices using the 
> userio
> +	  kernel module.
> +
> +	  To compile this driver as a module, choose M here: the 
> module will be
> +	  called userio.
> +
> +	  If you are unsure, say N.
> +
>  endif
> diff --git a/drivers/input/serio/Makefile 
> b/drivers/input/serio/Makefile
> index c600089..2374ef9 100644
> --- a/drivers/input/serio/Makefile
> +++ b/drivers/input/serio/Makefile
> @@ -30,3 +30,4 @@ obj-$(CONFIG_SERIO_APBPS2)	+= apbps2.o
>  obj-$(CONFIG_SERIO_OLPC_APSP)	+= olpc_apsp.o
>  obj-$(CONFIG_HYPERV_KEYBOARD)	+= hyperv-keyboard.o
>  obj-$(CONFIG_SERIO_SUN4I_PS2)	+= sun4i-ps2.o
> +obj-$(CONFIG_USERIO)		+= userio.o
> diff --git a/drivers/input/serio/userio.c 
> b/drivers/input/serio/userio.c
> new file mode 100644
> index 0000000..578b107
> --- /dev/null
> +++ b/drivers/input/serio/userio.c
> @@ -0,0 +1,261 @@
> +/*
> + * userio kernel serio device emulation module
> + * Copyright (C) 2015 Red Hat
> + * Copyright (C) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
> + *
> + * This program is free software; you can redistribute it and/or 
> modify it
> + * under the terms of the GNU Lesser General Public License as 
> published by the
> + * Free Software Foundation; either version 2 of the License, or (at 
> your
> + * option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful, 
> but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of 
> MERCHANTABILITY or FITNESS
> + * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
> License for more
> + * details.
> + */
> +#include <linux/circ_buf.h>
> +#include <linux/mutex.h>
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/serio.h>
> +#include <linux/slab.h>
> +#include <linux/fs.h>
> +#include <linux/miscdevice.h>
> +#include <linux/sched.h>
> +#include <linux/poll.h>
> +#include <linux/spinlock.h>
> +#include <uapi/linux/userio.h>
> +
> +#define USERIO_NAME "userio"
> +#define USERIO_BUFSIZE 16
> +
> +static const struct file_operations userio_fops;
> +static struct miscdevice userio_misc;
> +
> +struct userio_device {
> +	struct serio *serio;
> +
> +	bool running;
> +
> +	u8 head;
> +	u8 tail;
> +
> +	/*
> +	 * Since we need to copy from userspace when modifying the 
> tail and we
> +	 * don't want to lock up the serio driver during these 
> operations, we
> +	 * use two different locks
> +	 */
> +	spinlock_t head_lock;
> +	struct mutex tail_lock;
> +
> +	unsigned char buf[USERIO_BUFSIZE];
> +
> +	wait_queue_head_t waitq;
> +};
> +
> +/**
> + * userio_device_write - Write data from serio to a userio device in 
> userspace
> + * @id: The serio port for the userio device
> + * @val: The data to write to the device
> + */
> +static int userio_device_write(struct serio *id, unsigned char val)
> +{
> +	struct userio_device *userio = id->port_data;
> +	unsigned long flags;
> +
> +	if (!userio)
> +		return -1;
> +
> +	spin_lock_irqsave(&userio->head_lock, flags);
> +
> +	userio->buf[userio->head] = val;
> +	userio->head = (userio->head + 1) % USERIO_BUFSIZE;
> +
> +	spin_unlock_irqrestore(&userio->head_lock, flags);
> +
> +	if (userio->head == userio->tail)
> +		dev_warn(userio_misc.this_device,
> +			 "Buffer overflowed, userio client isn't 
> keeping up");
> +
> +	wake_up_interruptible(&userio->waitq);
> +
> +	return 0;
> +}
> +
> +static int userio_char_open(struct inode *inode, struct file *file)
> +{
> +	struct userio_device *userio;
> +
> +	userio = devm_kzalloc(userio_misc.this_device,
> +			      sizeof(struct userio_device), 
> GFP_KERNEL);
> +	if (!userio)
> +		return -ENOMEM;
> +
> +	spin_lock_init(&userio->head_lock);
> +	mutex_init(&userio->tail_lock);
> +	init_waitqueue_head(&userio->waitq);
> +
> +	userio->serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
> +	if (!userio->serio) {
> +		devm_kfree(userio_misc.this_device, userio);
> +		return -ENOMEM;
> +	}
> +
> +	userio->serio->write = userio_device_write;
> +	userio->serio->port_data = userio;
> +
> +	file->private_data = userio;
> +
> +	return 0;
> +}
> +
> +static int userio_char_release(struct inode *inode, struct file 
> *file)
> +{
> +	struct userio_device *userio = file->private_data;
> +
> +	if (userio->serio) {
> +		userio->serio->port_data = NULL;
> +
> +		if (userio->running)
> +			serio_unregister_port(userio->serio);
> +		else
> +			kfree(userio->serio);
> +	}
> +
> +	devm_kfree(userio_misc.this_device, userio);
> +
> +	return 0;
> +}
> +
> +static ssize_t userio_char_read(struct file *file, char __user 
> *buffer,
> +				size_t count, loff_t *ppos)
> +{
> +	struct userio_device *userio = file->private_data;
> +	int ret;
> +	size_t nonwrap_len, copylen;
> +
> +	if (!count)
> +		return 0;
> +
> +	if (file->f_flags & O_NONBLOCK && userio->head == userio
> ->tail)
> +		return -EAGAIN;
> +	else {
> +		ret = wait_event_interruptible(userio->waitq,
> +					       userio->head != 
> userio->tail);
> +
> +		if (ret)
> +			return ret;
> +	}
> +
> +	mutex_lock(&userio->tail_lock);
> +
> +	nonwrap_len = CIRC_CNT_TO_END(userio->head, userio->tail,
> +				      USERIO_BUFSIZE);
> +	copylen = min(nonwrap_len, count);
> +
> +	if (copy_to_user(buffer, &userio->buf[userio->tail], 
> copylen)) {
> +		mutex_unlock(&userio->tail_lock);
> +		return -EFAULT;
> +	}
> +
> +	userio->tail = (userio->tail + copylen) % USERIO_BUFSIZE;
> +
> +	mutex_unlock(&userio->tail_lock);
> +
> +	return copylen;
> +}
> +
> +static ssize_t userio_char_write(struct file *file, const char 
> __user *buffer,
> +				 size_t count, loff_t *ppos)
> +{
> +	struct userio_device *userio = file->private_data;
> +	struct userio_cmd cmd;
> +
> +	if (count < sizeof(cmd))
> +		return -EINVAL;
> +
> +	if (copy_from_user(&cmd, buffer, sizeof(cmd)))
> +		return -EFAULT;
> +
> +	switch (cmd.type) {
> +	case USERIO_CMD_REGISTER:
> +		if (!userio->serio->id.type) {
> +			dev_warn(userio_misc.this_device,
> +				 "No port type given on 
> /dev/userio\n");
> +
> +			return -EINVAL;
> +		}
> +		if (userio->running) {
> +			dev_warn(userio_misc.this_device,
> +				 "Begin command sent, but we're 
> already running\n");
> +
> +			return -EINVAL;
> +		}
> +
> +		userio->running = true;
> +		serio_register_port(userio->serio);
> +		break;
> +
> +	case USERIO_CMD_SET_PORT_TYPE:
> +		if (userio->running) {
> +			dev_warn(userio_misc.this_device,
> +				 "Can't change port type on an 
> already running userio instance\n");
> +
> +			return -EINVAL;
> +		}
> +
> +		userio->serio->id.type = cmd.data;
> +		break;
> +
> +	case USERIO_CMD_SEND_INTERRUPT:
> +		if (!userio->running) {
> +			dev_warn(userio_misc.this_device,
> +				 "The device must be registered 
> before sending interrupts\n");
> +
> +			return -EINVAL;
> +		}
> +
> +		serio_interrupt(userio->serio, cmd.data, 0);
> +		break;
> +
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return sizeof(cmd);
> +}
> +
> +static unsigned int userio_char_poll(struct file *file, poll_table 
> *wait)
> +{
> +	struct userio_device *userio = file->private_data;
> +
> +	poll_wait(file, &userio->waitq, wait);
> +
> +	if (userio->head != userio->tail)
> +		return POLLIN | POLLRDNORM;
> +
> +	return 0;
> +}
> +
> +static const struct file_operations userio_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= userio_char_open,
> +	.release	= userio_char_release,
> +	.read		= userio_char_read,
> +	.write		= userio_char_write,
> +	.poll		= userio_char_poll,
> +	.llseek		= no_llseek,
> +};
> +
> +static struct miscdevice userio_misc = {
> +	.fops	= &userio_fops,
> +	.minor	= MISC_DYNAMIC_MINOR,
> +	.name	= USERIO_NAME,
> +};
> +
> +MODULE_AUTHOR("Stephen Chandler Paul <thatslyude@gmail.com>");
> +MODULE_DESCRIPTION("userio");
> +MODULE_LICENSE("GPL");
> +
> +module_driver(userio_misc, misc_register, misc_deregister);
> diff --git a/include/uapi/linux/userio.h 
> b/include/uapi/linux/userio.h
> new file mode 100644
> index 0000000..da0a3d6
> --- /dev/null
> +++ b/include/uapi/linux/userio.h
> @@ -0,0 +1,42 @@
> +/*
> + * userio.h
> + * Copyright (C) 2015 Red Hat
> + * Copyright (C) 2015 Lyude (Stephen Chandler Paul) <
> cpaul@redhat.com>
> + *
> + * This program is free software; you can redistribute it and/or 
> modify it
> + * under the terms of the GNU Lesser General Public License as 
> published by the
> + * Free Software Foundation; either version 2 of the License, or (at 
> your
> + * option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful, 
> but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of 
> MERCHANTABILITY or FITNESS
> + * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
> License for more
> + * details.
> + *
> + * This is the public header used for user-space communication with 
> the userio
> + * driver. __attribute__((__packed__)) is used  for all structs to 
> keep ABI
> + * compatibility between all architectures.
> + */
> +
> +#ifndef _USERIO_H
> +#define _USERIO_H
> +
> +#include <linux/types.h>
> +
> +#define USERIO_CMD_REGISTER		0
> +#define USERIO_CMD_SET_PORT_TYPE	1
> +#define USERIO_CMD_SEND_INTERRUPT	2
> +
> +/*
> + * userio Commands
> + * All commands sent to /dev/userio are encoded using this 
> structure. The type
> + * field should contain a USERIO_CMD* value that indicates what kind 
> of command
> + * is being sent to userio. The data field should contain the 
> accompanying
> + * argument for the command, if there is one.
> + */
> +struct userio_cmd {
> +	__u8 type;
> +	__u8 data;
> +} __attribute__((__packed__));
> +
> +#endif /* !_USERIO_H */
Benjamin Tissoires July 22, 2015, 8:53 p.m. UTC | #2
On Wed, Jul 22, 2015 at 3:52 PM, Stephen Chandler Paul <cpaul@redhat.com> wrote:
> Debugging input devices, specifically laptop touchpads, can be tricky
> without having the physical device handy. Here we try to remedy that
> with userio. This module allows an application to connect to a character
> device provided by the kernel, and emulate any serio device. In
> combination with userspace programs that can record PS/2 devices and
> replay them through the /dev/userio device, this allows developers to
> debug driver issues on the PS/2 level with devices simply by requesting
> a recording from the user experiencing the issue without having to have
> the physical hardware in front of them.
>
> Signed-off-by: Stephen Chandler Paul <cpaul@redhat.com>
> ---

Thanks Chandler for the new version. I think we still need to enhance
the concurrency barriers here. See inline.

>  Documentation/input/userio.txt |  70 +++++++++++
>  MAINTAINERS                    |   6 +
>  drivers/input/serio/Kconfig    |  11 ++
>  drivers/input/serio/Makefile   |   1 +
>  drivers/input/serio/userio.c   | 261 +++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/userio.h    |  42 +++++++
>  6 files changed, 391 insertions(+)
>  create mode 100644 Documentation/input/userio.txt
>  create mode 100644 drivers/input/serio/userio.c
>  create mode 100644 include/uapi/linux/userio.h
>
> diff --git a/Documentation/input/userio.txt b/Documentation/input/userio.txt
> new file mode 100644
> index 0000000..0880c0f
> --- /dev/null
> +++ b/Documentation/input/userio.txt
> @@ -0,0 +1,70 @@
> +                             The userio Protocol
> +            (c) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
> +                             Sponsored by Red Hat
> +--------------------------------------------------------------------------------
> +
> +1. Introduction
> +~~~~~~~~~~~~~~~
> +  This module is intended to try to make the lives of input driver developers
> +easier by allowing them to test various serio devices (mainly the various
> +touchpads found on laptops) without having to have the physical device in front
> +of them. userio accomplishes this by allowing any privileged userspace program
> +to directly interact with the kernel's serio driver and control a virtual serio
> +port from there.
> +
> +2. Usage overview
> +~~~~~~~~~~~~~~~~~
> +  In order to interact with the userio kernel module, one simply opens the
> +/dev/userio character device in their applications. Commands are sent to the
> +kernel module by writing to the device, and any data received from the serio
> +driver is read as-is from the /dev/userio device. All of the structures and
> +macros you need to interact with the device are defined in <linux/userio.h> and
> +<linux/serio.h>.
> +
> +3. Command Structure
> +~~~~~~~~~~~~~~~~~~~~
> +  The struct used for sending commands to /dev/userio is as follows:
> +
> +       struct userio_cmd {
> +               __u8 type;
> +               __u8 data;
> +       };
> +
> +  "type" describes the type of command that is being sent. This can be any one
> +of the USERIO_CMD macros defined in <linux/userio.h>. "data" is the argument
> +that goes along with the command. In the event that the command doesn't have an
> +argument, this field can be left untouched and will be ignored by the kernel.
> +Each command should be sent by writing the struct directly to the character
> +device. In the event that the command you send is invalid, an error will be
> +returned by the character device and a more descriptive error will be printed
> +to the kernel log. Only one command can be sent at a time, any additional data
> +written to the character device after the initial command will be ignored.
> +  To close the virtual serio port, just close /dev/userio.
> +
> +4. Commands
> +~~~~~~~~~~~
> +
> +4.1 USERIO_CMD_REGISTER
> +~~~~~~~~~~~~~~~~~~~~~~~
> +  Registers the port with the serio driver and begins transmitting data back and
> +forth. Registration can only be performed once a port type is set with
> +USERIO_CMD_SET_PORT_TYPE. Has no argument.
> +
> +4.2 USERIO_CMD_SET_PORT_TYPE
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +  Sets the type of port we're emulating, where "data" is the port type being
> +set. Can be any of the macros from <linux/serio.h>. For example: SERIO_8042
> +would set the port type to be a normal PS/2 port.
> +
> +4.3 USERIO_CMD_SEND_INTERRUPT
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +  Sends an interrupt through the virtual serio port to the serio driver, where
> +"data" is the interrupt data being sent.
> +
> +5. Userspace tools
> +~~~~~~~~~~~~~~~~~~
> +  The userio userspace tools are able to record PS/2 devices using some of the
> +debugging information from i8042, and play back the devices on /dev/userio. The
> +latest version of these tools can be found at:
> +
> +       https://github.com/Lyude/ps2emu
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a226416..68a0977 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10877,6 +10877,12 @@ S:     Maintained
>  F:     drivers/media/v4l2-core/videobuf2-*
>  F:     include/media/videobuf2-*
>
> +VIRTUAL PS/2 DEVICE DRIVER
> +M:     Stephen Chandler Paul <thatslyude@gmail.com>
> +S:     Maintained
> +F:     drivers/input/serio/ps2emu.c
> +F:     include/uapi/linux/ps2emu.h
> +
>  VIRTIO CONSOLE DRIVER
>  M:     Amit Shah <amit.shah@redhat.com>
>  L:     virtualization@lists.linux-foundation.org
> diff --git a/drivers/input/serio/Kconfig b/drivers/input/serio/Kconfig
> index 200841b..22b8b58 100644
> --- a/drivers/input/serio/Kconfig
> +++ b/drivers/input/serio/Kconfig
> @@ -292,4 +292,15 @@ config SERIO_SUN4I_PS2
>           To compile this driver as a module, choose M here: the
>           module will be called sun4i-ps2.
>
> +config USERIO
> +       tristate "Virtual serio device support"
> +       help
> +         Say Y here if you want to emulate serio devices using the userio
> +         kernel module.
> +
> +         To compile this driver as a module, choose M here: the module will be
> +         called userio.
> +
> +         If you are unsure, say N.
> +
>  endif
> diff --git a/drivers/input/serio/Makefile b/drivers/input/serio/Makefile
> index c600089..2374ef9 100644
> --- a/drivers/input/serio/Makefile
> +++ b/drivers/input/serio/Makefile
> @@ -30,3 +30,4 @@ obj-$(CONFIG_SERIO_APBPS2)    += apbps2.o
>  obj-$(CONFIG_SERIO_OLPC_APSP)  += olpc_apsp.o
>  obj-$(CONFIG_HYPERV_KEYBOARD)  += hyperv-keyboard.o
>  obj-$(CONFIG_SERIO_SUN4I_PS2)  += sun4i-ps2.o
> +obj-$(CONFIG_USERIO)           += userio.o
> diff --git a/drivers/input/serio/userio.c b/drivers/input/serio/userio.c
> new file mode 100644
> index 0000000..578b107
> --- /dev/null
> +++ b/drivers/input/serio/userio.c
> @@ -0,0 +1,261 @@
> +/*
> + * userio kernel serio device emulation module
> + * Copyright (C) 2015 Red Hat
> + * Copyright (C) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU Lesser General Public License as published by the
> + * Free Software Foundation; either version 2 of the License, or (at your
> + * option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
> + * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
> + * details.
> + */
> +#include <linux/circ_buf.h>
> +#include <linux/mutex.h>
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/serio.h>
> +#include <linux/slab.h>
> +#include <linux/fs.h>
> +#include <linux/miscdevice.h>
> +#include <linux/sched.h>
> +#include <linux/poll.h>
> +#include <linux/spinlock.h>
> +#include <uapi/linux/userio.h>
> +
> +#define USERIO_NAME "userio"
> +#define USERIO_BUFSIZE 16
> +
> +static const struct file_operations userio_fops;
> +static struct miscdevice userio_misc;
> +
> +struct userio_device {
> +       struct serio *serio;
> +
> +       bool running;
> +
> +       u8 head;
> +       u8 tail;
> +
> +       /*
> +        * Since we need to copy from userspace when modifying the tail and we
> +        * don't want to lock up the serio driver during these operations, we
> +        * use two different locks
> +        */

My guts tell me that this is racy. You generally want to have a single
mutex/spinlock to protect your buffer. Having 2 might introduce
interesting complex problems...

> +       spinlock_t head_lock;
> +       struct mutex tail_lock;
> +
> +       unsigned char buf[USERIO_BUFSIZE];
> +
> +       wait_queue_head_t waitq;
> +};
> +
> +/**
> + * userio_device_write - Write data from serio to a userio device in userspace
> + * @id: The serio port for the userio device
> + * @val: The data to write to the device
> + */
> +static int userio_device_write(struct serio *id, unsigned char val)
> +{
> +       struct userio_device *userio = id->port_data;
> +       unsigned long flags;
> +
> +       if (!userio)
> +               return -1;
> +
> +       spin_lock_irqsave(&userio->head_lock, flags);
> +

I know Dmitry said that this could be called by several threads, but I
am not 100% sure.
This function is called by the serio driver, and I don't think we will
have more than one thread at a time in the serio driver (this would
raise interesting hardware behavior for a serial protocol).

Though protecting the head and the value here could be a good thing if
you protect also when you read them.

> +       userio->buf[userio->head] = val;
> +       userio->head = (userio->head + 1) % USERIO_BUFSIZE;
> +
> +       spin_unlock_irqrestore(&userio->head_lock, flags);
> +
> +       if (userio->head == userio->tail)
> +               dev_warn(userio_misc.this_device,
> +                        "Buffer overflowed, userio client isn't keeping up");
> +
> +       wake_up_interruptible(&userio->waitq);
> +
> +       return 0;
> +}
> +
> +static int userio_char_open(struct inode *inode, struct file *file)
> +{
> +       struct userio_device *userio;
> +
> +       userio = devm_kzalloc(userio_misc.this_device,
> +                             sizeof(struct userio_device), GFP_KERNEL);
> +       if (!userio)
> +               return -ENOMEM;
> +
> +       spin_lock_init(&userio->head_lock);
> +       mutex_init(&userio->tail_lock);
> +       init_waitqueue_head(&userio->waitq);
> +
> +       userio->serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
> +       if (!userio->serio) {
> +               devm_kfree(userio_misc.this_device, userio);
> +               return -ENOMEM;
> +       }
> +
> +       userio->serio->write = userio_device_write;
> +       userio->serio->port_data = userio;
> +
> +       file->private_data = userio;
> +
> +       return 0;
> +}
> +
> +static int userio_char_release(struct inode *inode, struct file *file)
> +{
> +       struct userio_device *userio = file->private_data;
> +
> +       if (userio->serio) {
> +               userio->serio->port_data = NULL;
> +
> +               if (userio->running)
> +                       serio_unregister_port(userio->serio);
> +               else
> +                       kfree(userio->serio);
> +       }
> +
> +       devm_kfree(userio_misc.this_device, userio);

Calling devm_kfree directly should always raise a big red warning. The
point of having managed memory is to avoid calling kfree. If you have
to, then you probably should not call devm_kzalloc() in the first
place.

> +
> +       return 0;
> +}
> +
> +static ssize_t userio_char_read(struct file *file, char __user *buffer,
> +                               size_t count, loff_t *ppos)
> +{
> +       struct userio_device *userio = file->private_data;
> +       int ret;
> +       size_t nonwrap_len, copylen;
> +
> +       if (!count)
> +               return 0;
> +
> +       if (file->f_flags & O_NONBLOCK && userio->head == userio->tail)

This section is not protected while you are accessing userio->tail.
I think it is still safe here, but I am not 100% sure.

> +               return -EAGAIN;
> +       else {
> +               ret = wait_event_interruptible(userio->waitq,
> +                                              userio->head != userio->tail);

I would protect this under the mutex, but OTOH, it might lead also to
some interesting lockups.

> +
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       mutex_lock(&userio->tail_lock);
> +
> +       nonwrap_len = CIRC_CNT_TO_END(userio->head, userio->tail,
> +                                     USERIO_BUFSIZE);
> +       copylen = min(nonwrap_len, count);
> +
> +       if (copy_to_user(buffer, &userio->buf[userio->tail], copylen)) {
> +               mutex_unlock(&userio->tail_lock);
> +               return -EFAULT;
> +       }
> +
> +       userio->tail = (userio->tail + copylen) % USERIO_BUFSIZE;
> +
> +       mutex_unlock(&userio->tail_lock);
> +
> +       return copylen;
> +}
> +
> +static ssize_t userio_char_write(struct file *file, const char __user *buffer,
> +                                size_t count, loff_t *ppos)
> +{
> +       struct userio_device *userio = file->private_data;
> +       struct userio_cmd cmd;
> +
> +       if (count < sizeof(cmd))
> +               return -EINVAL;
> +
> +       if (copy_from_user(&cmd, buffer, sizeof(cmd)))
> +               return -EFAULT;
> +

Starting from here

> +       switch (cmd.type) {
> +       case USERIO_CMD_REGISTER:
> +               if (!userio->serio->id.type) {
> +                       dev_warn(userio_misc.this_device,
> +                                "No port type given on /dev/userio\n");
> +
> +                       return -EINVAL;
> +               }
> +               if (userio->running) {
> +                       dev_warn(userio_misc.this_device,
> +                                "Begin command sent, but we're already running\n");
> +
> +                       return -EINVAL;
> +               }
> +
> +               userio->running = true;
> +               serio_register_port(userio->serio);
> +               break;
> +
> +       case USERIO_CMD_SET_PORT_TYPE:
> +               if (userio->running) {
> +                       dev_warn(userio_misc.this_device,
> +                                "Can't change port type on an already running userio instance\n");
> +
> +                       return -EINVAL;
> +               }
> +
> +               userio->serio->id.type = cmd.data;
> +               break;
> +
> +       case USERIO_CMD_SEND_INTERRUPT:
> +               if (!userio->running) {
> +                       dev_warn(userio_misc.this_device,
> +                                "The device must be registered before sending interrupts\n");
> +
> +                       return -EINVAL;
> +               }
> +
> +               serio_interrupt(userio->serio, cmd.data, 0);
> +               break;
> +
> +       default:
> +               return -EINVAL;
> +       }

... to here, you should protect this against several threads. You
don't want to register twice the serio port because 2 threads read
userio->running as false when issuing USERIO_CMD_REGISTER.
Likewise, there could be races between USERIO_CMD_SEND_INTERRUPT and
USERIO_CMD_REGISTER.

I don't think this user-space interface (both read and write) is time
critical, so I would simply put a lock before each interaction with
the internal state and release it when done.

> +
> +       return sizeof(cmd);
> +}
> +
> +static unsigned int userio_char_poll(struct file *file, poll_table *wait)
> +{
> +       struct userio_device *userio = file->private_data;
> +
> +       poll_wait(file, &userio->waitq, wait);
> +
> +       if (userio->head != userio->tail)
> +               return POLLIN | POLLRDNORM;
> +
> +       return 0;
> +}
> +
> +static const struct file_operations userio_fops = {
> +       .owner          = THIS_MODULE,
> +       .open           = userio_char_open,
> +       .release        = userio_char_release,
> +       .read           = userio_char_read,
> +       .write          = userio_char_write,
> +       .poll           = userio_char_poll,
> +       .llseek         = no_llseek,
> +};
> +
> +static struct miscdevice userio_misc = {
> +       .fops   = &userio_fops,
> +       .minor  = MISC_DYNAMIC_MINOR,
> +       .name   = USERIO_NAME,
> +};
> +
> +MODULE_AUTHOR("Stephen Chandler Paul <thatslyude@gmail.com>");
> +MODULE_DESCRIPTION("userio");
> +MODULE_LICENSE("GPL");
> +
> +module_driver(userio_misc, misc_register, misc_deregister);
> diff --git a/include/uapi/linux/userio.h b/include/uapi/linux/userio.h
> new file mode 100644
> index 0000000..da0a3d6
> --- /dev/null
> +++ b/include/uapi/linux/userio.h
> @@ -0,0 +1,42 @@
> +/*
> + * userio.h
> + * Copyright (C) 2015 Red Hat
> + * Copyright (C) 2015 Lyude (Stephen Chandler Paul) <cpaul@redhat.com>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU Lesser General Public License as published by the
> + * Free Software Foundation; either version 2 of the License, or (at your
> + * option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
> + * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
> + * details.
> + *
> + * This is the public header used for user-space communication with the userio
> + * driver. __attribute__((__packed__)) is used  for all structs to keep ABI
> + * compatibility between all architectures.
> + */
> +
> +#ifndef _USERIO_H
> +#define _USERIO_H
> +
> +#include <linux/types.h>
> +
> +#define USERIO_CMD_REGISTER            0
> +#define USERIO_CMD_SET_PORT_TYPE       1
> +#define USERIO_CMD_SEND_INTERRUPT      2
> +
> +/*
> + * userio Commands
> + * All commands sent to /dev/userio are encoded using this structure. The type
> + * field should contain a USERIO_CMD* value that indicates what kind of command
> + * is being sent to userio. The data field should contain the accompanying
> + * argument for the command, if there is one.
> + */
> +struct userio_cmd {
> +       __u8 type;
> +       __u8 data;
> +} __attribute__((__packed__));
> +
> +#endif /* !_USERIO_H */
> --
> 2.4.3
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-input" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Cheers,
Benjamin
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the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Dmitry Torokhov July 22, 2015, 9:39 p.m. UTC | #3
Hi Stephen,

On Wed, Jul 22, 2015 at 03:52:53PM -0400, Stephen Chandler Paul wrote:
> +static int userio_char_open(struct inode *inode, struct file *file)
> +{
> +	struct userio_device *userio;
> +
> +	userio = devm_kzalloc(userio_misc.this_device,
> +			      sizeof(struct userio_device), GFP_KERNEL);
> +	if (!userio)
> +		return -ENOMEM;

Never ever use devm_ API outside of device probe() calls because
devm-managed resources only freed after failed probe() or after remove()
callback on driver model device and not any other device (block, char,
etc) in the system.

> +
> +	spin_lock_init(&userio->head_lock);
> +	mutex_init(&userio->tail_lock);
> +	init_waitqueue_head(&userio->waitq);
> +
> +	userio->serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
> +	if (!userio->serio) {
> +		devm_kfree(userio_misc.this_device, userio);

And indeed here you have ot manually release the acquired resource. So
the only benefit you got form devm* is wasted resousrces.

> +		return -ENOMEM;
> +	}
> +
> +	userio->serio->write = userio_device_write;
> +	userio->serio->port_data = userio;
> +
> +	file->private_data = userio;
> +
> +	return 0;
> +}
> +
> +static int userio_char_release(struct inode *inode, struct file *file)
> +{
> +	struct userio_device *userio = file->private_data;
> +
> +	if (userio->serio) {
> +		userio->serio->port_data = NULL;

No need to reset, it is going away.

> +
> +		if (userio->running)
> +			serio_unregister_port(userio->serio);
> +		else
> +			kfree(userio->serio);
> +	}
> +
> +	devm_kfree(userio_misc.this_device, userio);
> +
> +	return 0;
> +}
> +
> +static ssize_t userio_char_read(struct file *file, char __user *buffer,
> +				size_t count, loff_t *ppos)
> +{
> +	struct userio_device *userio = file->private_data;
> +	int ret;
> +	size_t nonwrap_len, copylen;
> +
> +	if (!count)
> +		return 0;
> +
> +	if (file->f_flags & O_NONBLOCK && userio->head == userio->tail)
> +		return -EAGAIN;
> +	else {

This is racy. If there was data and other thread "stole" it here then
your O_NONBLOCK will block. See evdev_read() how you supposed to handle
this.

Thanks.

Patch
diff mbox

diff --git a/Documentation/input/userio.txt b/Documentation/input/userio.txt
new file mode 100644
index 0000000..0880c0f
--- /dev/null
+++ b/Documentation/input/userio.txt
@@ -0,0 +1,70 @@ 
+			      The userio Protocol
+	     (c) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
+			      Sponsored by Red Hat
+--------------------------------------------------------------------------------
+
+1. Introduction
+~~~~~~~~~~~~~~~
+  This module is intended to try to make the lives of input driver developers
+easier by allowing them to test various serio devices (mainly the various
+touchpads found on laptops) without having to have the physical device in front
+of them. userio accomplishes this by allowing any privileged userspace program
+to directly interact with the kernel's serio driver and control a virtual serio
+port from there.
+
+2. Usage overview
+~~~~~~~~~~~~~~~~~
+  In order to interact with the userio kernel module, one simply opens the
+/dev/userio character device in their applications. Commands are sent to the
+kernel module by writing to the device, and any data received from the serio
+driver is read as-is from the /dev/userio device. All of the structures and
+macros you need to interact with the device are defined in <linux/userio.h> and
+<linux/serio.h>.
+
+3. Command Structure
+~~~~~~~~~~~~~~~~~~~~
+  The struct used for sending commands to /dev/userio is as follows:
+
+	struct userio_cmd {
+		__u8 type;
+		__u8 data;
+	};
+
+  "type" describes the type of command that is being sent. This can be any one
+of the USERIO_CMD macros defined in <linux/userio.h>. "data" is the argument
+that goes along with the command. In the event that the command doesn't have an
+argument, this field can be left untouched and will be ignored by the kernel.
+Each command should be sent by writing the struct directly to the character
+device. In the event that the command you send is invalid, an error will be
+returned by the character device and a more descriptive error will be printed
+to the kernel log. Only one command can be sent at a time, any additional data
+written to the character device after the initial command will be ignored.
+  To close the virtual serio port, just close /dev/userio.
+
+4. Commands
+~~~~~~~~~~~
+
+4.1 USERIO_CMD_REGISTER
+~~~~~~~~~~~~~~~~~~~~~~~
+  Registers the port with the serio driver and begins transmitting data back and
+forth. Registration can only be performed once a port type is set with
+USERIO_CMD_SET_PORT_TYPE. Has no argument.
+
+4.2 USERIO_CMD_SET_PORT_TYPE
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  Sets the type of port we're emulating, where "data" is the port type being
+set. Can be any of the macros from <linux/serio.h>. For example: SERIO_8042
+would set the port type to be a normal PS/2 port.
+
+4.3 USERIO_CMD_SEND_INTERRUPT
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  Sends an interrupt through the virtual serio port to the serio driver, where
+"data" is the interrupt data being sent.
+
+5. Userspace tools
+~~~~~~~~~~~~~~~~~~
+  The userio userspace tools are able to record PS/2 devices using some of the
+debugging information from i8042, and play back the devices on /dev/userio. The
+latest version of these tools can be found at:
+
+	https://github.com/Lyude/ps2emu
diff --git a/MAINTAINERS b/MAINTAINERS
index a226416..68a0977 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10877,6 +10877,12 @@  S:	Maintained
 F:	drivers/media/v4l2-core/videobuf2-*
 F:	include/media/videobuf2-*
 
+VIRTUAL PS/2 DEVICE DRIVER
+M:	Stephen Chandler Paul <thatslyude@gmail.com>
+S:	Maintained
+F:	drivers/input/serio/ps2emu.c
+F:	include/uapi/linux/ps2emu.h
+
 VIRTIO CONSOLE DRIVER
 M:	Amit Shah <amit.shah@redhat.com>
 L:	virtualization@lists.linux-foundation.org
diff --git a/drivers/input/serio/Kconfig b/drivers/input/serio/Kconfig
index 200841b..22b8b58 100644
--- a/drivers/input/serio/Kconfig
+++ b/drivers/input/serio/Kconfig
@@ -292,4 +292,15 @@  config SERIO_SUN4I_PS2
 	  To compile this driver as a module, choose M here: the
 	  module will be called sun4i-ps2.
 
+config USERIO
+	tristate "Virtual serio device support"
+	help
+	  Say Y here if you want to emulate serio devices using the userio
+	  kernel module.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called userio.
+
+	  If you are unsure, say N.
+
 endif
diff --git a/drivers/input/serio/Makefile b/drivers/input/serio/Makefile
index c600089..2374ef9 100644
--- a/drivers/input/serio/Makefile
+++ b/drivers/input/serio/Makefile
@@ -30,3 +30,4 @@  obj-$(CONFIG_SERIO_APBPS2)	+= apbps2.o
 obj-$(CONFIG_SERIO_OLPC_APSP)	+= olpc_apsp.o
 obj-$(CONFIG_HYPERV_KEYBOARD)	+= hyperv-keyboard.o
 obj-$(CONFIG_SERIO_SUN4I_PS2)	+= sun4i-ps2.o
+obj-$(CONFIG_USERIO)		+= userio.o
diff --git a/drivers/input/serio/userio.c b/drivers/input/serio/userio.c
new file mode 100644
index 0000000..578b107
--- /dev/null
+++ b/drivers/input/serio/userio.c
@@ -0,0 +1,261 @@ 
+/*
+ * userio kernel serio device emulation module
+ * Copyright (C) 2015 Red Hat
+ * Copyright (C) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+ * details.
+ */
+#include <linux/circ_buf.h>
+#include <linux/mutex.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/serio.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <linux/sched.h>
+#include <linux/poll.h>
+#include <linux/spinlock.h>
+#include <uapi/linux/userio.h>
+
+#define USERIO_NAME "userio"
+#define USERIO_BUFSIZE 16
+
+static const struct file_operations userio_fops;
+static struct miscdevice userio_misc;
+
+struct userio_device {
+	struct serio *serio;
+
+	bool running;
+
+	u8 head;
+	u8 tail;
+
+	/*
+	 * Since we need to copy from userspace when modifying the tail and we
+	 * don't want to lock up the serio driver during these operations, we
+	 * use two different locks
+	 */
+	spinlock_t head_lock;
+	struct mutex tail_lock;
+
+	unsigned char buf[USERIO_BUFSIZE];
+
+	wait_queue_head_t waitq;
+};
+
+/**
+ * userio_device_write - Write data from serio to a userio device in userspace
+ * @id: The serio port for the userio device
+ * @val: The data to write to the device
+ */
+static int userio_device_write(struct serio *id, unsigned char val)
+{
+	struct userio_device *userio = id->port_data;
+	unsigned long flags;
+
+	if (!userio)
+		return -1;
+
+	spin_lock_irqsave(&userio->head_lock, flags);
+
+	userio->buf[userio->head] = val;
+	userio->head = (userio->head + 1) % USERIO_BUFSIZE;
+
+	spin_unlock_irqrestore(&userio->head_lock, flags);
+
+	if (userio->head == userio->tail)
+		dev_warn(userio_misc.this_device,
+			 "Buffer overflowed, userio client isn't keeping up");
+
+	wake_up_interruptible(&userio->waitq);
+
+	return 0;
+}
+
+static int userio_char_open(struct inode *inode, struct file *file)
+{
+	struct userio_device *userio;
+
+	userio = devm_kzalloc(userio_misc.this_device,
+			      sizeof(struct userio_device), GFP_KERNEL);
+	if (!userio)
+		return -ENOMEM;
+
+	spin_lock_init(&userio->head_lock);
+	mutex_init(&userio->tail_lock);
+	init_waitqueue_head(&userio->waitq);
+
+	userio->serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
+	if (!userio->serio) {
+		devm_kfree(userio_misc.this_device, userio);
+		return -ENOMEM;
+	}
+
+	userio->serio->write = userio_device_write;
+	userio->serio->port_data = userio;
+
+	file->private_data = userio;
+
+	return 0;
+}
+
+static int userio_char_release(struct inode *inode, struct file *file)
+{
+	struct userio_device *userio = file->private_data;
+
+	if (userio->serio) {
+		userio->serio->port_data = NULL;
+
+		if (userio->running)
+			serio_unregister_port(userio->serio);
+		else
+			kfree(userio->serio);
+	}
+
+	devm_kfree(userio_misc.this_device, userio);
+
+	return 0;
+}
+
+static ssize_t userio_char_read(struct file *file, char __user *buffer,
+				size_t count, loff_t *ppos)
+{
+	struct userio_device *userio = file->private_data;
+	int ret;
+	size_t nonwrap_len, copylen;
+
+	if (!count)
+		return 0;
+
+	if (file->f_flags & O_NONBLOCK && userio->head == userio->tail)
+		return -EAGAIN;
+	else {
+		ret = wait_event_interruptible(userio->waitq,
+					       userio->head != userio->tail);
+
+		if (ret)
+			return ret;
+	}
+
+	mutex_lock(&userio->tail_lock);
+
+	nonwrap_len = CIRC_CNT_TO_END(userio->head, userio->tail,
+				      USERIO_BUFSIZE);
+	copylen = min(nonwrap_len, count);
+
+	if (copy_to_user(buffer, &userio->buf[userio->tail], copylen)) {
+		mutex_unlock(&userio->tail_lock);
+		return -EFAULT;
+	}
+
+	userio->tail = (userio->tail + copylen) % USERIO_BUFSIZE;
+
+	mutex_unlock(&userio->tail_lock);
+
+	return copylen;
+}
+
+static ssize_t userio_char_write(struct file *file, const char __user *buffer,
+				 size_t count, loff_t *ppos)
+{
+	struct userio_device *userio = file->private_data;
+	struct userio_cmd cmd;
+
+	if (count < sizeof(cmd))
+		return -EINVAL;
+
+	if (copy_from_user(&cmd, buffer, sizeof(cmd)))
+		return -EFAULT;
+
+	switch (cmd.type) {
+	case USERIO_CMD_REGISTER:
+		if (!userio->serio->id.type) {
+			dev_warn(userio_misc.this_device,
+				 "No port type given on /dev/userio\n");
+
+			return -EINVAL;
+		}
+		if (userio->running) {
+			dev_warn(userio_misc.this_device,
+				 "Begin command sent, but we're already running\n");
+
+			return -EINVAL;
+		}
+
+		userio->running = true;
+		serio_register_port(userio->serio);
+		break;
+
+	case USERIO_CMD_SET_PORT_TYPE:
+		if (userio->running) {
+			dev_warn(userio_misc.this_device,
+				 "Can't change port type on an already running userio instance\n");
+
+			return -EINVAL;
+		}
+
+		userio->serio->id.type = cmd.data;
+		break;
+
+	case USERIO_CMD_SEND_INTERRUPT:
+		if (!userio->running) {
+			dev_warn(userio_misc.this_device,
+				 "The device must be registered before sending interrupts\n");
+
+			return -EINVAL;
+		}
+
+		serio_interrupt(userio->serio, cmd.data, 0);
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	return sizeof(cmd);
+}
+
+static unsigned int userio_char_poll(struct file *file, poll_table *wait)
+{
+	struct userio_device *userio = file->private_data;
+
+	poll_wait(file, &userio->waitq, wait);
+
+	if (userio->head != userio->tail)
+		return POLLIN | POLLRDNORM;
+
+	return 0;
+}
+
+static const struct file_operations userio_fops = {
+	.owner		= THIS_MODULE,
+	.open		= userio_char_open,
+	.release	= userio_char_release,
+	.read		= userio_char_read,
+	.write		= userio_char_write,
+	.poll		= userio_char_poll,
+	.llseek		= no_llseek,
+};
+
+static struct miscdevice userio_misc = {
+	.fops	= &userio_fops,
+	.minor	= MISC_DYNAMIC_MINOR,
+	.name	= USERIO_NAME,
+};
+
+MODULE_AUTHOR("Stephen Chandler Paul <thatslyude@gmail.com>");
+MODULE_DESCRIPTION("userio");
+MODULE_LICENSE("GPL");
+
+module_driver(userio_misc, misc_register, misc_deregister);
diff --git a/include/uapi/linux/userio.h b/include/uapi/linux/userio.h
new file mode 100644
index 0000000..da0a3d6
--- /dev/null
+++ b/include/uapi/linux/userio.h
@@ -0,0 +1,42 @@ 
+/*
+ * userio.h
+ * Copyright (C) 2015 Red Hat
+ * Copyright (C) 2015 Lyude (Stephen Chandler Paul) <cpaul@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+ * details.
+ *
+ * This is the public header used for user-space communication with the userio
+ * driver. __attribute__((__packed__)) is used  for all structs to keep ABI
+ * compatibility between all architectures.
+ */
+
+#ifndef _USERIO_H
+#define _USERIO_H
+
+#include <linux/types.h>
+
+#define USERIO_CMD_REGISTER		0
+#define USERIO_CMD_SET_PORT_TYPE	1
+#define USERIO_CMD_SEND_INTERRUPT	2
+
+/*
+ * userio Commands
+ * All commands sent to /dev/userio are encoded using this structure. The type
+ * field should contain a USERIO_CMD* value that indicates what kind of command
+ * is being sent to userio. The data field should contain the accompanying
+ * argument for the command, if there is one.
+ */
+struct userio_cmd {
+	__u8 type;
+	__u8 data;
+} __attribute__((__packed__));
+
+#endif /* !_USERIO_H */