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2026-07-12 10:17:17 -04:00
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+# Kernel 7.0 uinput regression: UI_DEV_SETUP required
+
+## Summary
+
+Kernel 7.0.0-22-generic broke the legacy uinput creation sequence.
+Sunshine's Inputtino and libevdev both use the old method and fail silently.
+
+## Pre-diagnostic: is uinput built-in or a module?
+
+Before running the C or Python diagnostic below, check if uinput is a loadable module or built into the kernel:
+
+```bash
+modinfo uinput 2>&1 | grep filename
+# "filename: (builtin)" → uinput is compiled into the kernel
+# "filename: /lib/modules/..." → uinput is a loadable module
+
+grep CONFIG_INPUT_UINPUT /boot/config-$(uname -r)
+# "CONFIG_INPUT_UINPUT=y" → built-in (no modprobe needed)
+# "CONFIG_INPUT_UINPUT=m" → module (modprobe uinput to load)
+```
+
+**If built-in:** `modprobe uinput` will succeed silently but `lsmod | grep uinput` will show nothing — this is expected. The device node at `/dev/uinput` exists regardless. Permissions (user in `input` group) are what matter. Skip any module-loading troubleshooting steps.
+
+**If a module:** `sudo modprobe uinput` and verify with `lsmod | grep uinput`. To persist across reboots: `echo "uinput" | sudo tee /etc/modules-load.d/uinput.conf`.
+
+## Root cause
+
+The uinput subsystem on kernel 7.0+ REQUIRES `UI_DEV_SETUP` ioctl before
+`UI_DEV_CREATE`. The old method (writing `struct uinput_user_dev` via write()
+or calling `UI_DEV_CREATE` without prior setup) is rejected with EINVAL (-22).
+
+Sunshine v2026.516.143833 links against libevdev 1.13.6, which uses the old method.
+Inputtino (Sunshine's actual input backend, not libevdev) also uses the old method.
+
+## Diagnostic (C test)
+
+```c
+#include <linux/uinput.h>
+int fd = open("/dev/uinput", O_WRONLY);
+ioctl(fd, UI_DEV_CREATE);  // FAILS: EINVAL on kernel 7.0
+
+// Correct kernel 7.0 sequence:
+struct uinput_setup usetup;
+memset(&usetup, 0, sizeof(usetup));
+usetup.id.bustype = BUS_USB;
+strcpy(usetup.name, "test");
+ioctl(fd, UI_DEV_SETUP, &usetup);  // NEW: Required on 7.0+
+ioctl(fd, UI_DEV_CREATE);          // SUCCESS
+```
+
+## Diagnostic (Python test)
+
+```python
+import ctypes
+libevdev = ctypes.CDLL('libevdev.so.2')
+dev = libevdev.libevdev_new()
+libevdev.libevdev_set_name(dev, b'test')
+libevdev.libevdev_enable_event_type(dev, 1)
+uifd = ctypes.c_int(-1)
+ret = libevdev.libevdev_uinput_create_from_device(dev, 3, ctypes.byref(uifd))
+# Returns -25 (ENOTTY) on kernel 7.0 — uinput broken
+# Returns 0 on kernel 6.x — uinput works
+```
+
+## Why the LD_PRELOAD shim may not work
+
+The shim (`scripts/uinput-shim.c`) intercepts `libevdev_uinput_create_from_device`.
+However, Sunshine's PRIMARY input backend is **Inputtino** (subproject inside Sunshine
+binary), not libevdev. Inputtino creates keyboard/mouse devices through a separate
+code path that may not call through libevdev's public API. If the shim is deployed
+and input still doesn't work, Inputtino is bypassing it.
+
+## Proven workarounds
+
+1. **xdotool bridge** (`scripts/sunshine-input-bridge.py`) — tails Sunshine log,
+   injects via xdotool XTEST. Works on any kernel.
+2. **Steam Remote Play** (`templates/remote_play.vdf`) — different protocol,
+   no uinput involved.
+3. **Boot kernel 6.x** if available.
+
+## Kernel version
+
+Tested broken: 7.0.0-22-generic (Ubuntu 26.04)
+Tested working: Linux 6.x series