Date:   Sun, 26 Mar 2017 13:21:14 -0300
From:   Marcos Paulo de Souza <marcos.souza.org@...il.com>
To:     Peter Hutterer <peter.hutterer@...-t.net>
Cc:     corbet@....net, linux-doc@...r.kernel.org,
        dmitry.torokhov@...il.com, linux-input@...r.kernel.org,
        benjamin.tissoires@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Documentation: Input: Add uinput documentation

On Fri, Mar 24, 2017 at 02:39:13PM +1000, Peter Hutterer wrote:
> as usual, reading through these things multiple times means one spots a
> couple of different things. sorry about that.
> 
> On Fri, Mar 24, 2017 at 12:34:59AM -0300, Marcos Paulo de Souza wrote:
> > Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@...il.com>
> > ---
> >  Documentation/input/uinput.rst | 196 +++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 196 insertions(+)
> >  create mode 100644 Documentation/input/uinput.rst
> > 
> > diff --git a/Documentation/input/uinput.rst b/Documentation/input/uinput.rst
> > new file mode 100644
> > index 0000000..eb79b77
> > --- /dev/null
> > +++ b/Documentation/input/uinput.rst
> > @@ -0,0 +1,196 @@
> > +=============
> > +uinput module
> > +=============
> > +
> > +Introduction
> > +============
> > +
> > +uinput is a kernel module that makes possible to create and handle input devices
> 
> typo: makes *it* possible.
> 
> replace "to create and handle" with "to emulate", the rest is in the next
> sentence anyway

Fixed.

> 
> > +from userspace. By writing to the module's /dev/uinput (or /dev/input/uinput), a
> > +process can create a virtual device with specific capabilities.
> > +Once created, the process can send events through that virtual device.
> > +
> > +Interface
> > +=========
> > +
> > +::
> > +
> > +  linux/uinput.h
> > +
> > +The uinput header defines ioctls to create, setup and destroy virtual devices.
> > +
> > +libevdev
> > +========
> > +
> > +libevdev is a wrapper library for evdev devices, making uinput setup easier
> > +by skipping a lot of ioctl calls. When dealing with uinput, libevdev is the best
> > +alternative over accessing uinput directly, and it is less error prone.
> 
> "libevdev is a wrapper library for evdev devices that provides interfaces to
> create uinput devices and send events. libevdev is less error-prone than
> accessing uinput directly and should be considered for new software".

Much better. Fixed.

> 
> > +
> > +For examples and more information about libevdev:
> > +https://cgit.freedesktop.org/libevdev
> > +
> 
> Please use https://www.freedesktop.org/software/libevdev/doc/latest/
> (which needs a link to the git repo, I'll fix that in a minute)

Fixed.

> 
> > +Examples
> > +========
> > +
> > +1.0 Keyboard events
> > +-------------------
> > +
> > +This first example shows how to create a new virtual device and how to send a
> > +key event. All default imports and error handlers were removed for the sake of
> > +simplicity.
> > +
> > +.. code-block:: c
> > +
> > +   #include <linux/uinput.h>
> > +
> > +   int fd;
> > +
> > +   void emit(int type, int code, int val)
> > +   {
> > +        struct input_event ie;
> > +
> > +        ie.type = type;
> > +        ie.code = code;
> > +        ie.value = val;
> > +        /* below timestamp values are ignored */
> > +        ie.time.tv_sec = 0;
> > +        ie.time.tv_usec = 0;
> > +
> > +        write(fd, &ie, sizeof(ie));
> > +   }
> > +
> > +   int main() {
> > +        struct uinput_setup usetup;
> > +
> > +        fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
> > +
> > +        /* the ioctls below enables the to be created device to key
> > +         * events, in this case the space key
> > +         **/
> 
> the comment terminator doesn't look right

Fixed.

> 
> > +        ioctl(fd, UI_SET_EVBIT, EV_KEY);
> > +        ioctl(fd, UI_SET_KEYBIT, KEY_SPACE);
> > +
> > +        memset(&usetup, 0, sizeof(usetup));
> > +        usetup.id.bustype = BUS_USB;
> > +        usetup.id.vendor = 0x1234; /* sample vendor */
> 
> add a sample product id too please
Added.

> 
> > +        strcpy(usetup.name, "Example device");
> > +
> > +        ioctl(fd, UI_DEV_SETUP, &usetup);
> > +        ioctl(fd, UI_DEV_CREATE);
> > +
> > +        /* UI_DEV_CREATE causes the kernel to create the device nodes for this
> 
> "On UI_DEV_CREATE the kernel creates the device nodes..."
Fixed.

> 
> > +         * device. Insert a pause so that userspace has time to detect,
> > +         * initialize the new device, and can start to listen to events from
> > +         * this device
> > +         **/
> 
> the comment terminator doesn't look right
> 
> note: the actual pause is missing now :)

I thought you wanted just the warning, but ok, I added back the sleep
call :)

> 
> > +
> > +        /* key press, report the event, send key release, and report again */
> > +        emit(EV_KEY, KEY_SPACE, 1);
> > +        emit(EV_SYN, SYN_REPORT, 0);
> > +        emit(EV_KEY, KEY_SPACE, 0);
> > +        emit(EV_SYN, SYN_REPORT, 0);
> 
> come to think of it, you probably need a pause here too, iirc a caller may
> get ENODEV before reading the key events otherwise.

We need a sleep call after each emitted event?

> 
> > +
> > +        ioctl(fd, UI_DEV_DESTROY);
> > +        close(fd);
> > +
> > +        return 0;
> > +   }
> > +
> > +2.0 Mouse movements
> > +-------------------
> > +
> > +This example shows how to create a virtual device that behaves like a physical
> > +mouse.
> > +
> > +.. code-block:: c
> > +
> > +    #include <linux/uinput.h>
> > +
> > +    /* emit function is identical to of the first example */
> > +
> > +    struct uinput_setup usetup;
> > +    int i = 50;
> > +
> > +    fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
> > +
> > +    /* enable mouse button left and relative events */
> > +    ioctl(fd, UI_SET_EVBIT, EV_KEY);
> > +    ioctl(fd, UI_SET_KEYBIT, BTN_LEFT);
> > +
> > +    ioctl(fd, UI_SET_EVBIT, EV_REL);
> > +    ioctl(fd, UI_SET_RELBIT, REL_X);
> > +    ioctl(fd, UI_SET_RELBIT, REL_Y);
> > +
> > +    memset(&usetup, 0, sizeof(usetup));
> > +    usetup.id.bustype = BUS_USB;
> > +    usetup.id.vendor = 0x1234; /* sample vendor */
> > +    strcpy(usetup.name, "Example device");
> > +
> > +    ioctl(fd, UI_DEV_SETUP, &usetup);
> > +    ioctl(fd, UI_DEV_CREATE);
> > +
> > +    /* UI_DEV_CREATE causes the kernel to create the device nodes for this
> > +     * device. Insert a pause so that userspace has time to detect,
> > +     * initialize the new device, and can start to listen to events from
> > +     * this device
> > +     **/
> > +
> > +    /* moves the mouse diagonally, 5 units per axis */
> > +    while (i--) {
> > +        emit(EV_REL, REL_X, 5);
> > +        emit(EV_REL, REL_Y, 5);
> > +        emit(EV_SYN, SYN_REPORT, 0);
> > +        usleep(15000);
> > +    }
> > +
> > +    ioctl(fd, UI_DEV_DESTROY);
> > +    close(fd);
> > +
> > +    return 0;
> > +
> > +3.0 uinput old interface
> > +------------------------
> > +
> > +Before kernel 4.5, uinput didn't have an ioctl to setup a virtual device. When
> > +running a version prior to 4.5, the user needs to fill a different struct and
> > +call write on the uinput file descriptor.
> 
> I think this should really include the version check.

Uhg, I forgot this one again. Fixed here.

Sending a new version soon.

> 
> Cheers,
>    Peter
> 
> > +
> > +.. code-block:: c
> > +
> > +    #include <linux/uinput.h>
> > +
> > +    /* emit function is identical to of the first example */
> > +
> > +    struct uinput_user_dev uud;
> > +
> > +    fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
> > +
> > +    /* the ioctls below enables the to be created device to key
> > +     * events, in this case the space key
> > +     **/
> > +    ioctl(fd, UI_SET_EVBIT, EV_KEY);
> > +    ioctl(fd, UI_SET_KEYBIT, KEY_SPACE);
> > +
> > +    memset(&uud, 0, sizeof(uud));
> > +    snprintf(uud.name, UINPUT_MAX_NAME_SIZE, "uinput old interface");
> > +    write(fd, &uud, sizeof(uud));
> > +
> > +    ioctl(fd, UI_DEV_CREATE);
> > +
> > +    /* UI_DEV_CREATE causes the kernel to create the device nodes for this
> > +     * device. Insert a pause so that userspace has time to detect,
> > +     * initialize the new device, and can start to listen to events from
> > +     * this device
> > +     **/
> > +
> > +    /* key press, report the event, send key release, and report again */
> > +    emit(EV_KEY, KEY_SPACE, 1);
> > +    emit(EV_SYN, SYN_REPORT, 0);
> > +    emit(EV_KEY, KEY_SPACE, 0);
> > +    emit(EV_SYN, SYN_REPORT, 0);
> > +
> > +    ioctl(fd, UI_DEV_DESTROY);
> > +    close(fd);
> > +
> > +    return 0;
> > +
> > -- 
> > 2.9.3
> > 

-- 
Thanks,
	Marcos

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