Re: [PATCH v2] Documentation: Input: Add uinput documentation

From: Marcos Paulo de Souza
Date: Sun Mar 26 2017 - 12:22:40 EST

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@xxxxxxxxx>
> > ---
> > 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