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authorMarcos Paulo de Souza <marcos.souza.org@gmail.com>2017-04-24 16:19:49 -0700
committerDmitry Torokhov <dmitry.torokhov@gmail.com>2017-04-24 16:50:37 -0700
commitaea415b1d10ea25779a100da639b3e3989080971 (patch)
treef796656ed00dad76f23850c5091bab20702f17a7 /Documentation/input/uinput.rst
parent1613976bbdc560b5ed906af9976ae476996550c3 (diff)
downloadlinux-aea415b1d10ea25779a100da639b3e3989080971.tar.bz2
Input: add uinput documentation
Add description of uinput module with a few examples. Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
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+=============
+uinput module
+=============
+
+Introduction
+============
+
+uinput is a kernel module that makes it possible to emulate input devices
+from userspace. By writing to /dev/uinput (or /dev/input/uinput) device, a
+process can create a virtual input device with specific capabilities. Once
+this virtual device is created, the process can send events through it,
+that will be delivered to userspace and in-kernel consumers.
+
+Interface
+=========
+
+::
+
+ linux/uinput.h
+
+The uinput header defines ioctls to create, set up, and destroy virtual
+devices.
+
+libevdev
+========
+
+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.
+
+For examples and more information about libevdev:
+https://www.freedesktop.org/software/libevdev/doc/latest/
+
+Examples
+========
+
+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>
+
+ void emit(int fd, int type, int code, int val)
+ {
+ struct input_event ie;
+
+ ie.type = type;
+ ie.code = code;
+ ie.value = val;
+ /* timestamp values below are ignored */
+ ie.time.tv_sec = 0;
+ ie.time.tv_usec = 0;
+
+ write(fd, &ie, sizeof(ie));
+ }
+
+ int main(void)
+ {
+ struct uinput_setup usetup;
+
+ int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
+
+
+ /*
+ * The ioctls below will enable the device that is about to be
+ * created, to pass key events, in this case the space key.
+ */
+ 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 */
+ usetup.id.product = 0x5678; /* sample product */
+ strcpy(usetup.name, "Example device");
+
+ ioctl(fd, UI_DEV_SETUP, &usetup);
+ ioctl(fd, UI_DEV_CREATE);
+
+ /*
+ * On UI_DEV_CREATE the kernel will create the device node for this
+ * device. We are inserting a pause here so that userspace has time
+ * to detect, initialize the new device, and can start listening to
+ * the event, otherwise it will not notice the event we are about
+ * to send. This pause is only needed in our example code!
+ */
+ sleep(1);
+
+ /* Key press, report the event, send key release, and report again */
+ emit(fd, EV_KEY, KEY_SPACE, 1);
+ emit(fd, EV_SYN, SYN_REPORT, 0);
+ emit(fd, EV_KEY, KEY_SPACE, 0);
+ emit(fd, EV_SYN, SYN_REPORT, 0);
+
+ /*
+ * Give userspace some time to read the events before we destroy the
+ * device with UI_DEV_DESTOY.
+ */
+ sleep(1);
+
+ ioctl(fd, UI_DEV_DESTROY);
+ close(fd);
+
+ return 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 */
+
+ int main(void)
+ {
+ struct uinput_setup usetup;
+ int i = 50;
+
+ int 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 */
+ usetup.id.product = 0x5678; /* sample product */
+ strcpy(usetup.name, "Example device");
+
+ ioctl(fd, UI_DEV_SETUP, &usetup);
+ ioctl(fd, UI_DEV_CREATE);
+
+ /*
+ * On UI_DEV_CREATE the kernel will create the device node for this
+ * device. We are inserting a pause here so that userspace has time
+ * to detect, initialize the new device, and can start listening to
+ * the event, otherwise it will not notice the event we are about
+ * to send. This pause is only needed in our example code!
+ */
+ sleep(1);
+
+ /* Move the mouse diagonally, 5 units per axis */
+ while (i--) {
+ emit(fd, EV_REL, REL_X, 5);
+ emit(fd, EV_REL, REL_Y, 5);
+ emit(fd, EV_SYN, SYN_REPORT, 0);
+ usleep(15000);
+ }
+
+ /*
+ * Give userspace some time to read the events before we destroy the
+ * device with UI_DEV_DESTOY.
+ */
+ sleep(1);
+
+ ioctl(fd, UI_DEV_DESTROY);
+ close(fd);
+
+ return 0;
+ }
+
+
+uinput old interface
+--------------------
+
+Before uinput version 5, there wasn't a dedicated ioctl to set up a virtual
+device. Programs supportinf older versions of uinput interface need to fill
+a uinput_user_dev structure and write it to the uinput file descriptor to
+configure the new uinput device. New code should not use the old interface
+but interact with uinput via ioctl calls, or use libevdev.
+
+.. code-block:: c
+
+ #include <linux/uinput.h>
+
+ /* emit function is identical to of the first example */
+
+ int main(void)
+ {
+ struct uinput_user_dev uud;
+ int version, rc, fd;
+
+ fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
+ rc = ioctl(fd, UI_GET_VERSION, &version);
+
+ if (rc == 0 && version >= 5) {
+ /* use UI_DEV_SETUP */
+ return 0;
+ }
+
+ /*
+ * The ioctls below will enable the device that is about to be
+ * created, to pass 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 will create the device node for this
+ * device. We are inserting a pause here so that userspace has time
+ * to detect, initialize the new device, and can start listening to
+ * the event, otherwise it will not notice the event we are about
+ * to send. This pause is only needed in our example code!
+ */
+ sleep(1);
+
+ /* Key press, report the event, send key release, and report again */
+ emit(fd, EV_KEY, KEY_SPACE, 1);
+ emit(fd, EV_SYN, SYN_REPORT, 0);
+ emit(fd, EV_KEY, KEY_SPACE, 0);
+ emit(fd, EV_SYN, SYN_REPORT, 0);
+
+ /*
+ * Give userspace some time to read the events before we destroy the
+ * device with UI_DEV_DESTOY.
+ */
+ sleep(1);
+
+ ioctl(fd, UI_DEV_DESTROY);
+
+ close(fd);
+ return 0;
+ }
+