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SubjectRe: [PATCH v3] Documentation: Input: Add uinput documentation
On Sun, Mar 26, 2017 at 01:48:12PM -0300, Marcos Paulo de Souza wrote:
> Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
> ---
> v2 -> v3:
> Changes in libevdev's description (suggested by Peter)
> Added uinput version check when using the old interface (suggested by Peter)
> Removed section numbers from sections, sphinx creates these indexes
> (suggestion by Jon)
>
> v1 -> v2:
> Changes all over the place, including better descriptions (suggested by Peter)
> Added comments about the need of a sleep call (suggested by Peter)
>


[...]

tested mouse/keyboard - works as expected, thanks. I found it slightly
confusing though that the mouse example wasn't wrapped in main() but still had a
return 0 at the bottom. This code will never change once it's in the doc, so
I'm not sure skipping things is really that useful here.

> +uinput old interface
> +--------------------
> +
> +Before uinput version 5, there wasn't a proper ioctl to setup a virtual device.
> +In this case, the user neesa to fill a different struct and call write o the
> +uinput file descriptor to configure the new uinput device.
> +
> +.. code-block:: c
> +
> + #include <linux/uinput.h>
> +
> + /* emit function is identical to of the first example */
> +
> + struct uinput_user_dev uud;
> + int version;
> +
> + fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
> + ioctl(fd, UI_GET_VERSION, &version);
> +
> + if (version < 5) {

this won't work on all kernels. UI_GET_VERSION was added in version 4, on
kernels before you get rc == -1 and errno EINVAL. You can only check
for >= 4. Please make sure the example compiles and works on an older
kernel, otherwise there's no point shipping it.

Cheers,
Peter

> + /*
> + * 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);
> +
> + /*
> + * On UI_DEV_CREATE the kernel creates 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
> + */
> + sleep(1);
> +
> + /* 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
>

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