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+.. include:: <isonum.txt>
+
+===================
+The userio Protocol
+===================
+
+
+:Copyright: |copy| 2015 Stephen Chandler Paul <thatslyude@gmail.com>
+
+Sponsored by Red Hat
+
+
+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.
+
+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>.
+
+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.
+
+Commands
+========
+
+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.
+
+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.
+
+USERIO_CMD_SEND_INTERRUPT
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Sends an interrupt through the virtual serio port to the serio driver, where
+``data`` is the interrupt data being sent.
+
+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