Add readonly parameter to InputDevice and writable parameter to list_devices/is_device

Author: xz-dev

src/evdev/device.py

@@ -109,19 +109,26 @@ class InputDevice(EventIO, Generic[_AnyStr]):
 
     __slots__ = ("path", "fd", "info", "name", "phys", "uniq", "_rawcapabilities", "version", "ff_effects_count")
 
-    def __init__(self, dev: Union[_AnyStr, "os.PathLike[_AnyStr]"]):
+    def __init__(self, dev: Union[_AnyStr, "os.PathLike[_AnyStr]"], readonly: bool = False):
         """
         Arguments
         ---------
         dev : str|bytes|PathLike
           Path to input device
+        readonly : bool
+          If True, the device is opened in read-only mode (``O_RDONLY``)
+          without attempting ``O_RDWR`` first. This avoids triggering
+          firmware side-effects (such as LED state re-assertion) on
+          certain hardware. Default is False.
         """
 
         #: Path to input device.
         self.path: _AnyStr = dev if not hasattr(dev, "__fspath__") else dev.__fspath__()
 
         # Certain operations are possible only when the device is opened in read-write mode.
         try:
+            if readonly:
+                raise OSError
             fd = os.open(dev, os.O_RDWR | os.O_NONBLOCK)
         except OSError:
             fd = os.open(dev, os.O_RDONLY | os.O_NONBLOCK)

src/evdev/util.py

@@ -9,15 +9,33 @@
 from .events import InputEvent, event_factory, KeyEvent, RelEvent, AbsEvent, SynEvent
 
 
-def list_devices(input_device_dir: Union[str, bytes, os.PathLike] = "/dev/input") -> List[str]:
-    """List readable character devices in ``input_device_dir``."""
+def list_devices(input_device_dir: Union[str, bytes, os.PathLike] = "/dev/input", writable: bool = True) -> List[str]:
+    """List readable (and optionally writable) character devices in ``input_device_dir``.
+
+    Arguments
+    ---------
+    input_device_dir : str|bytes|PathLike
+      Path to the input device directory. Default is ``/dev/input``.
+    writable : bool
+      If True (default), only list devices that are both readable and
+      writable. If False, list all readable devices.
+    """
 
     fns = glob.glob("{}/event*".format(input_device_dir))
-    return list(filter(is_device, fns))
+    return list(filter(lambda fn: is_device(fn, writable=writable), fns))
+
 
+def is_device(fn: Union[str, bytes, os.PathLike], writable: bool = True) -> bool:
+    """Check if ``fn`` is a readable (and optionally writable) character device.
 
-def is_device(fn: Union[str, bytes, os.PathLike]) -> bool:
-    """Check if ``fn`` is a readable and writable character device."""
+    Arguments
+    ---------
+    fn : str|bytes|PathLike
+      Path to the device file.
+    writable : bool
+      If True (default), also check for write access. If False, only
+      check for read access.
+    """
 
     if not os.path.exists(fn):
         return False
@@ -26,7 +44,8 @@ def is_device(fn: Union[str, bytes, os.PathLike]) -> bool:
     if not stat.S_ISCHR(m):
         return False
 
-    if not os.access(fn, os.R_OK | os.W_OK):
+    access = os.R_OK | os.W_OK if writable else os.R_OK
+    if not os.access(fn, access):
         return False
 
     return True