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Date: Wed, 22 Jul 2015 16:53:38 -0400
From: Benjamin Tissoires <benjamin.tissoires@...il.com>
To: Stephen Chandler Paul <cpaul@...hat.com>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mauro Carvalho Chehab <mchehab@....samsung.com>,
Greg KH <gregkh@...uxfoundation.org>,
Arnd Bergmann <arnd@...db.de>, Joe Perches <joe@...ches.com>,
Jiri Slaby <jslaby@...e.com>,
Vishnu Patekar <vishnupatekar0510@...il.com>,
Sebastian Ott <sebott@...ux.vnet.ibm.com>,
linux-doc@...r.kernel.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
linux-input <linux-input@...r.kernel.org>,
linux-api@...r.kernel.org,
Benjamin Tissoires <benjamin.tissoires@...hat.com>,
Hans de Goede <hdegoede@...hat.com>
Subject: Re: [RFC v3 1/1] Input: Add userio module
On Wed, Jul 22, 2015 at 3:52 PM, Stephen Chandler Paul <cpaul@...hat.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@...hat.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@...il.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@...il.com>
> +S: Maintained
> +F: drivers/input/serio/ps2emu.c
> +F: include/uapi/linux/ps2emu.h
> +
> VIRTIO CONSOLE DRIVER
> M: Amit Shah <amit.shah@...hat.com>
> L: virtualization@...ts.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@...il.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@...il.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@...hat.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
>
> --
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Cheers,
Benjamin
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