Hi Zhai, On Mon, Mar 15, 2021 at 07:58:58PM +0800, Zhai Zhaoxuan wrote: > > In the real world, I think, it is nearly impossible that a physical > device contains so many keys or buttons. > > But I think a virtual device may need this. Such as a server remote > management card, it simulates a virtual keyboard, > registers keys and forwards all keys from user's computer to server. > And the user's computer may have any keys. So the card needs to > register all possible keys and send them to the kernel. I believe the best approach is to forward input devices to the remote system one by one, exactly as they are on the local end, instead of trying to crate a frankenstein monster out of them. You will not be able to do that in a meaningful way anyway, as for example a touchscreen needs to be handled differently from a touchpad, and if you smash them all together into one composite device you will get a mess on your hands. > > I have tried to register only all **known** keys instead of all keys, > but it still fails on the kernel. > (The userspace source file has been placed in attachment.) > > > What functionality does it allow that we do not have today? > > If programs are unable to register all known keys on only 1 uinput > device, programs have to register > keys on two or more devices. But this may result in unexpected behavior. > > For example, the program registers Key A on device1, and registers Key > B on device2. > When the program needs to send a key combination A+B to a target > application, it has to: > 1. emit Key A down on device 1 > 2. emit Key B down on device 2 > 3. SYN_REPORT on device 1 > 4. SYN_REPORT on device 2 > 5. emit Key A up on device 1 > 6. emit Key B up on device 2 > 7. SYN_REPORT on device 1 > 8. SYN_REPORT on device 2 > > Then, the target application polls input events on both devices 1 & 2. > It reads on device 1, and gets Key A pressed down and then released, > so it does feature A. > Then, it reads on device 2, and gets Key B pressed down and then > released, so it does feature B. > Finally, the target application loses the A+B key combination. Which is exactly what would happen in a real life with 2 hardware devices. Thanks. -- Dmitry
