Input: add userio module

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>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

3 files changed, 300 insertions, 0 deletions

diff --git a/drivers/input/serio/Kconfig b/drivers/input/serio/Kconfig
index 200841b77edb..c3d05b4d3118 100644
--- a/drivers/input/serio/Kconfig
+++ b/drivers/input/serio/Kconfig
@@ -292,4 +292,18 @@ config SERIO_SUN4I_PS2
 	  To compile this driver as a module, choose M here: the
 	  module will be called sun4i-ps2.
 
+config USERIO
+	tristate "User space serio port driver support"
+	help
+	  Say Y here if you want to support user level drivers for serio
+	  subsystem accessible under char device 10:240 - /dev/userio. Using
+	  this facility userspace programs can implement serio ports that
+	  will be used by the standard in-kernel serio consumer drivers,
+	  such as psmouse and atkbd.
+
+	  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 c600089b7a34..2374ef9b33d7 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 000000000000..df1fd41860ac
--- /dev/null
+++ b/drivers/input/serio/userio.c
@@ -0,0 +1,285 @@
+/*
+ * 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 <uapi/linux/userio.h>
+
+#define USERIO_NAME		"userio"
+#define USERIO_BUFSIZE		16
+
+static struct miscdevice userio_misc;
+
+struct userio_device {
+	struct serio *serio;
+	struct mutex mutex;
+
+	bool running;
+
+	u8 head;
+	u8 tail;
+
+	spinlock_t buf_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;
+
+	spin_lock_irqsave(&userio->buf_lock, flags);
+
+	userio->buf[userio->head] = val;
+	userio->head = (userio->head + 1) % USERIO_BUFSIZE;
+
+	if (userio->head == userio->tail)
+		dev_warn(userio_misc.this_device,
+			 "Buffer overflowed, userio client isn't keeping up");
+
+	spin_unlock_irqrestore(&userio->buf_lock, flags);
+
+	wake_up_interruptible(&userio->waitq);
+
+	return 0;
+}
+
+static int userio_char_open(struct inode *inode, struct file *file)
+{
+	struct userio_device *userio;
+
+	userio = kzalloc(sizeof(struct userio_device), GFP_KERNEL);
+	if (!userio)
+		return -ENOMEM;
+
+	mutex_init(&userio->mutex);
+	spin_lock_init(&userio->buf_lock);
+	init_waitqueue_head(&userio->waitq);
+
+	userio->serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
+	if (!userio->serio) {
+		kfree(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->running) {
+		/*
+		 * Don't free the serio port here, serio_unregister_port()
+		 * does it for us.
+		 */
+		serio_unregister_port(userio->serio);
+	} else {
+		kfree(userio->serio);
+	}
+
+	kfree(userio);
+
+	return 0;
+}
+
+static ssize_t userio_char_read(struct file *file, char __user *user_buffer,
+				size_t count, loff_t *ppos)
+{
+	struct userio_device *userio = file->private_data;
+	int error;
+	size_t nonwrap_len, copylen;
+	unsigned char buf[USERIO_BUFSIZE];
+	unsigned long flags;
+
+	/*
+	 * By the time we get here, the data that was waiting might have
+	 * been taken by another thread. Grab the buffer lock and check if
+	 * there's still any data waiting, otherwise repeat this process
+	 * until we have data (unless the file descriptor is non-blocking
+	 * of course).
+	 */
+	for (;;) {
+		spin_lock_irqsave(&userio->buf_lock, flags);
+
+		nonwrap_len = CIRC_CNT_TO_END(userio->head,
+					      userio->tail,
+					      USERIO_BUFSIZE);
+		copylen = min(nonwrap_len, count);
+		if (copylen) {
+			memcpy(buf, &userio->buf[userio->tail], copylen);
+			userio->tail = (userio->tail + copylen) %
+							USERIO_BUFSIZE;
+		}
+
+		spin_unlock_irqrestore(&userio->buf_lock, flags);
+
+		if (nonwrap_len)
+			break;
+
+		/* buffer was/is empty */
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		/*
+		 * count == 0 is special - no IO is done but we check
+		 * for error conditions (see above).
+		 */
+		if (count == 0)
+			return 0;
+
+		error = wait_event_interruptible(userio->waitq,
+						 userio->head != userio->tail);
+		if (error)
+			return error;
+	}
+
+	if (copylen)
+		if (copy_to_user(user_buffer, buf, copylen))
+			return -EFAULT;
+
+	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;
+	int error;
+
+	if (count != sizeof(cmd)) {
+		dev_warn(userio_misc.this_device, "Invalid payload size\n");
+		return -EINVAL;
+	}
+
+	if (copy_from_user(&cmd, buffer, sizeof(cmd)))
+		return -EFAULT;
+
+	error = mutex_lock_interruptible(&userio->mutex);
+	if (error)
+		return error;
+
+	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");
+
+			error = -EINVAL;
+			goto out;
+		}
+
+		if (userio->running) {
+			dev_warn(userio_misc.this_device,
+				 "Begin command sent, but we're already running\n");
+			error = -EBUSY;
+			goto out;
+		}
+
+		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");
+			error = -EBUSY;
+			goto out;
+		}
+
+		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");
+			error = -ENODEV;
+			goto out;
+		}
+
+		serio_interrupt(userio->serio, cmd.data, 0);
+		break;
+
+	default:
+		error = -EOPNOTSUPP;
+		goto out;
+	}
+
+out:
+	mutex_unlock(&userio->mutex);
+	return error ?: count;
+}
+
+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	= USERIO_MINOR,
+	.name	= USERIO_NAME,
+};
+module_driver(userio_misc, misc_register, misc_deregister);
+
+MODULE_ALIAS_MISCDEV(USERIO_MINOR);
+MODULE_ALIAS("devname:" USERIO_NAME);
+
+MODULE_AUTHOR("Stephen Chandler Paul <thatslyude@gmail.com>");
+MODULE_DESCRIPTION("Virtual Serio Device Support");
+MODULE_LICENSE("GPL");