在Python3中定义与pyudev/evdev兼容的文件描述符

Hey there! Let’s work through that Bluetooth button issue you’re facing. You’ve got connection detection working, but button presses aren’t registering—and you’re right to suspect the evdev file descriptor setup for select is the culprit. Here’s how to troubleshoot and fix this:

First, Rule Out System-Level Issues #

Before diving into code, let’s make sure the hardware and OS are behaving:

1. Check the evdev node & test events manually
   After connecting your Bluetooth button, run these commands:

   # List all input devices
   ls /dev/input/event*
   # Install evtest if you haven't already
   sudo apt install evtest
   # Test each event node until you find your button
   sudo evtest /dev/input/eventX
   

   If evtest can pick up button presses, the problem is in your code. If not, re-pair the button or check Bluetooth logs with dmesg | grep Bluetooth for errors.

2. Fix permissions
   Regular users often don’t have access to /dev/input nodes. Either run your script with sudo, or add your user to the input group (requires a reboot to take effect):

   sudo usermod -aG input $USER
   

Adjust Your evdev & select Logic #

Your pyudev setup for connection detection is a good start, but we need to properly grab the evdev device’s file descriptor and use it with select. Here’s a revised code snippet with key fixes:

import functools
import pyudev
import evdev
from select import select

def handle_key_presses(device):
    """Process incoming key events from the Bluetooth button"""
    for event in device.read_loop():
        if event.type == evdev.ecodes.EV_KEY:
            key_data = evdev.categorize(event)
            # Print key state (pressed/released)
            status = "pressed" if key_data.keystate == key_data.key_down else "released"
            print(f"Button {key_data.keycode}: {status}")

def on_button_connected(context, device):
    """Triggered when the Bluetooth button connects"""
    # Target only input event devices (Bluetooth buttons are HID input devices)
    if device.subsystem == "input" and device.device_type == "event":
        try:
            # Create an evdev device object from the node path
            btn_device = evdev.InputDevice(device.device_node)
            print(f"Connected to button: {btn_device.name}")

            # Use select to listen for events on the device's file descriptor
            while True:
                # Listen for readable events (button presses trigger this)
                readable, _, _ = select([btn_device.fd], [], [])
                if btn_device.fd in readable:
                    handle_key_presses(btn_device)
        except Exception as err:
            print(f"Error handling device: {str(err)}")

# Set up pyudev to monitor input device connections
context = pyudev.Context()
monitor = pyudev.Monitor.from_netlink(context)
monitor.filter_by(subsystem="input")

# Start monitoring for new devices
observer = pyudev.MonitorObserver(monitor, callback=functools.partial(on_button_connected, context))
observer.start()

# Keep the script running
try:
    while True:
        pass
except KeyboardInterrupt:
    print("\nStopping monitor...")
    observer.stop()

Key Fixes Explained: #

• Proper evdev Device Initialization: We use device.device_node (from pyudev) to create an evdev.InputDevice—this gives us a valid file descriptor via btn_device.fd that works with select.
• Select Listening: We pass the device’s fd to select and wait for it to become readable (which happens when a button is pressed/released).
• Event Filtering: We only process EV_KEY events to ignore irrelevant input data.

Extra Checks If It Still Fails #

• Update your Python packages to the latest versions:

  pip install --upgrade pyudev evdev
  

• Verify your Bluetooth button uses a standard HID profile—some custom buttons may require additional driver setup.
• Check system logs with journalctl -u bluetooth.service for connection-related errors.

内容的提问来源于stack exchange，提问作者Pôm'