MicroPython bindings for libudev

udev.py

# SPDX-License-Identifier: MIT
# Copyright (c) 2019 David Lechner <david@pybricks.com>

import ffi

from uerrno import ENOENT

_udev = ffi.open('libudev.so.1')
_libc = ffi.open('libc.so.6')
_errno = _libc.var("i", "errno")


class Udev():
    _new = _udev.func('p', 'udev_new', '')
    _unref = _udev.func('p', 'udev_unref', 'p')

    def __init__(self):
        self._handle = Udev._new()
        if not self._handle:
            raise OSError(_errno.get())

    # must be called manually! Use context manager!
    def __del__(self):
        if self._handle:
            self._handle = Udev._unref(self._handle)

    def __enter__(self):
        return self

    def __exit__(self, *args):
        self.__del__()

    def scan(self, subsystem, **kwargs):
        """Scans for matching devices.

        Parameters
        ----------
        subsystem : string
            The subsystem (name of class or bus) to scan.
        **kwargs
            Property name/value pairs to match.

        Yields
        ------
        Device
            The matching devices.
        """
        with Enumerate(self) as e:
            e.add_match_subsystem(subsystem)
            for k, v in kwargs.items():
                e.add_match_property(k, v)
            try:
                e.scan_devices()
            except OSError as err:
                # not sure why we get ENOENT even on success
                if err.args[0] != ENOENT:
                    raise err

            # NB: don't capture e in closure since it is freed by context
            # manager when we return from this method
            paths = list(e.list())

            def iter():
                for p in paths:
                    yield Device.from_syspath(self, p)

            return iter()


class Enumerate():
    _new = _udev.func('p', 'udev_enumerate_new', 'p')
    _unref = _udev.func('p', 'udev_enumerate_unref', 'p')
    _add_match_subsystem = _udev.func('p', 'udev_enumerate_add_match_subsystem', 'ps')
    _add_match_property = _udev.func('i', 'udev_enumerate_add_match_property', 'pss')
    _scan_devices = _udev.func('i', 'udev_enumerate_scan_devices', 'p')
    _get_list_entry = _udev.func('p', 'udev_enumerate_get_list_entry', 'p')

    def __init__(self, udev):
        self._handle = Enumerate._new(udev._handle)
        if not self._handle:
            raise OSError(_errno.get())

    # must be called manually! Use context manager!
    def __del__(self):
        if self._handle:
            self._handle = Enumerate._unref(self._handle)

    def __enter__(self):
        return self

    def __exit__(self, *args):
        self.__del__()

    def add_match_subsystem(self, subsystem):
        err = Enumerate._add_match_subsystem(self._handle, subsystem)
        if err < 0:
            raise OSError(-err)

    def add_match_property(self, name, value):
        err = Enumerate._add_match_property(self._handle, name, value)
        if err < 0:
            raise OSError(-err)

    def scan_devices(self):
        err = Enumerate._scan_devices(self._handle)
        if err < 0:
            raise OSError(-err)

    def list(self):
        handle = Enumerate._get_list_entry(self._handle)
        if not handle:
            raise OSError(_errno.get())

        def iter(entry):
            while entry:
                yield entry.name
                entry = entry.next

        return iter(ListEntry(handle))


class Device():
    _new_from_syspath = _udev.func('p', 'udev_device_new_from_syspath', 'ps')
    _unref = _udev.func('p', 'udev_device_unref', 'p')
    _get_devnode = _udev.func('s', 'udev_device_get_devnode', 'p')

    @staticmethod
    def from_syspath(udev, syspath):
        handle = Device._new_from_syspath(udev._handle, syspath)
        if not handle:
            raise OSError(_errno.get())
        return Device(handle)

    def __init__(self, handle):
        self._handle = handle

    # must be called manually! Use context manager!
    def __del__(self):
        if self._handle:
            self._handle = Device._unref(self._handle)

    def __enter__(self):
        return self

    def __exit__(self, *args):
        self.__del__()

    @property
    def devnode(self):
        return Device._get_devnode(self._handle)


class Monitor():
    _new_from_netlink = _udev.func('p', 'udev_monitor_new_from_netlink', 'ps')
    _unref = _udev.func('p', 'udev_monitor_unref', 'p')

    def __init__(self, udev):
        self._handle = Monitor._new_from_netlink(udev._handle, 'udev')
        if not self._handle:
            raise OSError(_errno.get())

    # must be called manually! Use context manager!
    def __del__(self):
        if self._handle:
            self._handle = Monitor._unref(self._handle)

    def __enter__(self):
        return self

    def __exit__(self, *args):
        self.__del__()


class ListEntry():
    _get_next = _udev.func('p', 'udev_list_entry_get_next', 'p')
    _get_name = _udev.func('s', 'udev_list_entry_get_name', 'p')
    _get_value = _udev.func('s', 'udev_list_entry_get_value', 'p')

    def __init__(self, handle):
        self._handle = handle

    @property
    def next(self):
        handle = ListEntry._get_next(self._handle)
        return ListEntry(handle) if handle else None

    @property
    def name(self):
        return ListEntry._get_name(self._handle)

    @property
    def value(self):
        return ListEntry._get_value(self._handle)