[PATCH v3] Documentation: Input: Add uinput documentation

[Marcos Paulo de Souza]

Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@xxxxxxxxx>
---
 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)
 

 Documentation/input/uinput.rst | 207 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 207 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..f606989
--- /dev/null
+++ b/Documentation/input/uinput.rst
@@ -0,0 +1,207 @@
+=============
+uinput module
+=============
+
+Introduction
+============
+
+uinput is a kernel module that makes it possible to emulate input devices 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 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>
+
+   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
+         */
+        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 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;
+   }
+
+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 */
+    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 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);
+
+    /* 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;
+
+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) {
+        /*
+         * 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