Android Keyevent is defined in the KeyEvent.java screenshot corresponding to public static final int KEYCODE_SYSRQ = 120;
adb shell input keyevent SYSRQ
Linux Scancode is defined in input-event-codes.h #define KEY_SCALE 120. It can be seen that it does not correspond.
Originally, I wanted to double-click the fingerprint to realize the screenshot function, but found that reporting scancode 120 was not enough. Later, I learned that the codes of Android and Linux are different.
At the beginning, the method I thought of was to report the Linux Scancdoe volume down key and power key KEY_VOLUMEDOWN + KEY_POWER at the same time. Later, I learned that there is a key value implicit kl file
According to the above flowchart, we can know that the fingerprint does not have vendorid and prodcutid, so the name: uinput-fpc is directly passed, and all corresponding files are uinput-fpc.kl
. It is processed by EventHub.cpp, see the flow chart
(1)open /dev/uinput
(2)ioctl UI_SET_EVBIT -> set_bit
(2)ioctl UI_SET_KEYBIT -> set_bit
(3)write udev->name(uinput-fpc) -> uinput_setup_device_legacy
(4)ioctl UI_DEV_CREATE -> input_register_device
(5)write ev.type ev.code ev.value -> uinput_inject_event -> input_event
# Double Tap
-key 306 BUTTON_C
+key 306 SYSRQ
adb push uinput-fpc.kl system/usr/keylayout
