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Add some sections in the DESIGN.md for topics I want to talk about.

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Johannes Leupolz 2025-12-07 22:11:47 +00:00
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5
README.md
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@ -115,11 +115,6 @@ It reliably demonstrates the core concept — exposing `/dev/uinput` devices ins
Provide a deb/rpm package for simple deployment.
* [ ] **Check for compatibility with steam runtime:**
https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/blob/main/steam-runtime-tools/input-device.c
https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/blob/main/docs/container-runtime.md
https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/blob/main/docs/ld-library-path-runtime.md
https://github.com/ValveSoftware/steam-for-linux/issues/10175?utm_source=chatgpt.com
https://github.com/ValveSoftware/steam-for-linux/issues/8042
* [ ] **Forward known controller pids automatically:**
The main reason that vuinputd overrides pids is to ensure that those are not used by the host by accident, especially for keyboards that otherwise might get a seat assigned. This is irrelevant for gamepads. So the pids of known gamepads can just be forwarded. This is relevant for the 360 input devices that are created by steam.

49
docs/DESIGN.md
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@ -564,9 +564,11 @@ Library used by wolf and sunshine
#### 5.3.2 Steam
https://github.com/games-on-whales/inputtino
Library used by wolf and sunshine
https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/blob/main/steam-runtime-tools/input-device.c
https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/blob/main/docs/container-runtime.md
https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/blob/main/docs/ld-library-path-runtime.md
https://github.com/ValveSoftware/steam-for-linux/issues/10175
https://github.com/ValveSoftware/steam-for-linux/issues/8042
### 5.4 Applications that use the created devices
@ -574,15 +576,37 @@ Library used by wolf and sunshine
https://github.com/libsdl-org/SDL/blob/main/src/joystick/linux/SDL_sysjoystick.c
https://github.com/libsdl-org/SDL/blob/main/src/joystick/SDL_joystick.c
#### 5.4.2 libudev and netlink
#### 5.4.3 libinput
https://github.com/systemd/systemd/tree/main/src/libudev
https://insujang.github.io/2018-11-27/udev-device-manager-for-the-linux-kernel-in-userspace/
https://games-on-whales.github.io/wolf/stable/dev/fake-udev.html
https://github.com/JohnCMcDonough/virtual-gamepad
#### 5.4.3 libinput, libevdev
https://gitlab.freedesktop.org/libinput/libinput/-/tree/main/src?ref_type=heads
https://gitlab.freedesktop.org/libevdev/libevdev/-/blob/master/libevdev/libevdev-uinput.c?ref_type=heads
#### 5.4.4. Proton
## 6. Alternative Approaches
https://github.com/GloriousEggroll/proton-ge-custom/blob/master/docs/CONTROLLERS.md
### 6.1 trace accesses of /dev/uinput with eBPF
## 6. HIDAPI
https://github.com/libusb/hidapi
https://abeltra.me/blog/inputtino-uhid-1/
## 7. Alternative Approaches
### 7.1 trace accesses of /dev/uinput with eBPF
**Idea (short):** attach an eBPF program to the syscall tracepoint for `ioctl` (`tracepoint/syscalls/sys_enter_ioctl`), filter by container cgroup, and send small events (pid, tgid, fd, cmd, timestamp, short payload sample) to userspace using the BPF ring buffer. A privileged host agent consumes the ringbuf events, duplicates the target FD via `pidfd_getfd()` and proceeds with UI_GET_SYSNAME / sysfs resolution to retrieve the sys-path and the dev-path. Having the dev-path and the pid of the container, the solution could proceed as in the current solution.
@ -606,11 +630,20 @@ Inside the trace program you will typically use:
The **`pidfd_getfd()`** syscall (introduced in Linux 5.6, see `man pidfd_getfd(2)`) allows one process to **duplicate a file descriptor from another process** into its own FD table. It takes a *pidfd* (obtained via `pidfd_open()` or from `CLONE_PIDFD`), the target FD number in the remote process, and optional flags. The resulting descriptor refers to the **same open file description**—sharing offset, status flags, and driver state—exactly as if the target process had called `dup()`. Permission checks apply: the caller must either share credentials (same UID) or hold `CAP_SYS_PTRACE` or an equivalent capability over the target. This makes `pidfd_getfd()` the canonical and race-free way to inspect or reuse another process’s device handles (for example, to run `UI_GET_SYSNAME` on a client apps' fd on `/dev/uinput` ) without invasive ptrace tricks.
### 6.2 LD_PRELOAD
### 7.2 LD_PRELOAD
See src/fake-uinput/README.md on wolf
https://github.com/games-on-whales/wolf/issues/81
https://github.com/games-on-whales/wolf/pull/88
https://github.com/zerofltexx/wolf/commit/5b3282ceef6373c5afd2a860365c886fa942f59c#diff-2446d8f27f6ac4efff38510458548cea92179eddf38c187f5ad90d6bdd4b3d69
https://github.com/zerofltexx/wolf/commit/5b3282ceef6373c5afd2a860365c886fa942f59c#diff-2446d8f27f6ac4efff38510458548cea92179eddf38c187f5ad90d6bdd4b3d69
### 7.3 Custom kernel modul
https://github.com/dkms-project/dkms
https://github.com/torvalds/linux/blob/master/drivers/input/misc/uinput.c
https://lore.kernel.org/linux-bluetooth/20191201145357.ybq5gfty4ulnfasq@pali/t/#u