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| 1 | +#!/usr/bin/env python3 |
| 2 | +""" |
| 3 | +evdev-holder: Keep evdev input device file descriptors permanently open. |
| 4 | +
|
| 5 | +Workaround for LED pulsing on certain hardware (e.g. Tuxedo Stellaris 15 Gen3). |
| 6 | +
|
| 7 | +Root cause: |
| 8 | + When all fds to /dev/input/eventX are closed, the kernel's evdev->open count |
| 9 | + drops to 0. The next open() triggers: |
| 10 | + evdev_open_device() -> input_open_device() -> dev->open() |
| 11 | + which calls the hardware driver callback (e.g. hidinput_open -> hid_hw_open). |
| 12 | + On affected firmware (e.g. Tuxedo Stellaris EC), this driver reinitialization |
| 13 | + causes a visible LED pulse as a side effect. |
| 14 | +
|
| 15 | +Fix: |
| 16 | + By keeping at least one fd open per device, evdev->open stays >= 1. Subsequent |
| 17 | + opens see a truthy evdev->open++ and skip input_open_device() entirely, so the |
| 18 | + LED re-assertion path is never reached. |
| 19 | +
|
| 20 | +See: |
| 21 | + https://www.reddit.com/r/tuxedocomputers/comments/1rtj3c9/ |
| 22 | + https://github.com/gvalkov/python-evdev/pull/251 |
| 23 | +
|
| 24 | +Usage: |
| 25 | + sudo python3 evdev_holder.py # foreground |
| 26 | + sudo python3 evdev_holder.py --quiet # suppress info messages |
| 27 | +
|
| 28 | +Pure stdlib Python. No external dependencies. |
| 29 | +""" |
| 30 | + |
| 31 | +import argparse |
| 32 | +import glob |
| 33 | +import logging |
| 34 | +import os |
| 35 | +import signal |
| 36 | +import sys |
| 37 | +import time |
| 38 | + |
| 39 | +DEVPATH = "/dev/input/event*" |
| 40 | +DEFAULT_INTERVAL = 5 # seconds |
| 41 | + |
| 42 | +log = logging.getLogger("evdev-holder") |
| 43 | + |
| 44 | + |
| 45 | +def discover_devices(): |
| 46 | + """Return sorted list of all /dev/input/event* paths.""" |
| 47 | + return sorted(glob.glob(DEVPATH)) |
| 48 | + |
| 49 | + |
| 50 | +def open_device(path): |
| 51 | + """Open a device read-only + nonblock. Returns fd or None on failure.""" |
| 52 | + try: |
| 53 | + fd = os.open(path, os.O_RDONLY | os.O_NONBLOCK) |
| 54 | + return fd |
| 55 | + except OSError as e: |
| 56 | + log.warning("cannot open %s: %s", path, e) |
| 57 | + return None |
| 58 | + |
| 59 | + |
| 60 | +def fd_is_alive(fd): |
| 61 | + """Check if a held fd is still valid (device not unplugged).""" |
| 62 | + try: |
| 63 | + os.fstat(fd) |
| 64 | + return True |
| 65 | + except OSError: |
| 66 | + return False |
| 67 | + |
| 68 | + |
| 69 | +def close_fd(fd): |
| 70 | + """Close a file descriptor, ignoring errors.""" |
| 71 | + try: |
| 72 | + os.close(fd) |
| 73 | + except OSError: |
| 74 | + pass |
| 75 | + |
| 76 | + |
| 77 | +class EvdevHolder: |
| 78 | + def __init__(self, interval=DEFAULT_INTERVAL): |
| 79 | + # path -> fd |
| 80 | + self.held = {} |
| 81 | + self.interval = interval |
| 82 | + |
| 83 | + def scan(self): |
| 84 | + """Open any new devices not already held. Drop dead ones.""" |
| 85 | + # prune dead fds |
| 86 | + dead = [p for p, fd in self.held.items() if not fd_is_alive(fd)] |
| 87 | + for path in dead: |
| 88 | + log.info("device removed: %s", path) |
| 89 | + close_fd(self.held.pop(path)) |
| 90 | + |
| 91 | + # open new devices |
| 92 | + for path in discover_devices(): |
| 93 | + if path not in self.held: |
| 94 | + fd = open_device(path) |
| 95 | + if fd is not None: |
| 96 | + self.held[path] = fd |
| 97 | + log.info("holding: %s (fd=%d)", path, fd) |
| 98 | + |
| 99 | + def close_all(self): |
| 100 | + """Close all held file descriptors.""" |
| 101 | + for path, fd in self.held.items(): |
| 102 | + log.debug("releasing: %s (fd=%d)", path, fd) |
| 103 | + close_fd(fd) |
| 104 | + count = len(self.held) |
| 105 | + self.held.clear() |
| 106 | + return count |
| 107 | + |
| 108 | + def run(self): |
| 109 | + """Main loop: scan, sleep, repeat.""" |
| 110 | + self.scan() |
| 111 | + log.info("initial scan: holding %d device(s)", len(self.held)) |
| 112 | + |
| 113 | + while True: |
| 114 | + time.sleep(self.interval) |
| 115 | + self.scan() |
| 116 | + |
| 117 | + |
| 118 | +def main(): |
| 119 | + parser = argparse.ArgumentParser( |
| 120 | + description="Hold evdev input devices open to prevent LED pulsing on affected hardware." |
| 121 | + ) |
| 122 | + parser.add_argument( |
| 123 | + "--quiet", "-q", |
| 124 | + action="store_true", |
| 125 | + help="Only show warnings and errors.", |
| 126 | + ) |
| 127 | + parser.add_argument( |
| 128 | + "--interval", |
| 129 | + type=float, |
| 130 | + default=DEFAULT_INTERVAL, |
| 131 | + help=f"Device rescan interval in seconds (default: {DEFAULT_INTERVAL}).", |
| 132 | + ) |
| 133 | + args = parser.parse_args() |
| 134 | + |
| 135 | + # logging setup |
| 136 | + handler = logging.StreamHandler(sys.stderr) |
| 137 | + handler.setFormatter(logging.Formatter("[evdev-holder] %(message)s")) |
| 138 | + log.addHandler(handler) |
| 139 | + log.setLevel(logging.WARNING if args.quiet else logging.INFO) |
| 140 | + |
| 141 | + holder = EvdevHolder(interval=args.interval) |
| 142 | + |
| 143 | + # graceful shutdown |
| 144 | + def shutdown(signum, _frame): |
| 145 | + signame = signal.Signals(signum).name |
| 146 | + log.info("received %s, releasing all devices...", signame) |
| 147 | + count = holder.close_all() |
| 148 | + log.info("released %d device(s), exiting", count) |
| 149 | + sys.exit(0) |
| 150 | + |
| 151 | + signal.signal(signal.SIGTERM, shutdown) |
| 152 | + signal.signal(signal.SIGINT, shutdown) |
| 153 | + |
| 154 | + log.info("starting (rescan interval: %.1fs)", args.interval) |
| 155 | + holder.run() |
| 156 | + |
| 157 | + |
| 158 | +if __name__ == "__main__": |
| 159 | + main() |
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