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Edit File: discover.py
# -*- coding: utf-8 -*- # Copyright (C) 2015 mulhern <amulhern@redhat.com> # This library is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by the # Free Software Foundation; either version 2.1 of the License, or (at your # option) any later version. # This library is distributed in the hope that it will be useful, but WITHOUT # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or # FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License # for more details. # You should have received a copy of the GNU Lesser General Public License # along with this library; if not, write to the Free Software Foundation, # Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA """ pyudev.discover =============== Tools to discover a device given limited information. .. moduleauthor:: mulhern <amulhern@redhat.com> """ from __future__ import absolute_import from __future__ import division from __future__ import print_function from __future__ import unicode_literals import abc import functools import os import re import six from pyudev._errors import DeviceNotFoundError from pyudev.device import Devices def wrap_exception(func): """ Allow Device discovery methods to return None instead of raising an exception. """ @functools.wraps(func) def the_func(*args, **kwargs): """ Returns result of calling ``func`` on ``args``, ``kwargs``. Returns None if ``func`` raises :exc:`DeviceNotFoundError`. """ try: return func(*args, **kwargs) except DeviceNotFoundError: return None return the_func @six.add_metaclass(abc.ABCMeta) class Hypothesis(object): """ Represents a hypothesis about the meaning of the device identifier. """ @classmethod @abc.abstractmethod def match(cls, value): # pragma: no cover """ Match the given string according to the hypothesis. The purpose of this method is to obtain a value corresponding to ``value`` if that is possible. It may use a regular expression, but in general it should just return ``value`` and let the lookup method sort out the rest. :param str value: the string to inspect :returns: the matched thing or None if unmatched :rtype: the type of lookup's key parameter or NoneType """ raise NotImplementedError() @classmethod @abc.abstractmethod def lookup(cls, context, key): # pragma: no cover """ Lookup the given string according to the hypothesis. :param Context context: the pyudev context :param key: a key with which to lookup the device :type key: the type of match's return value if not None :returns: a list of Devices obtained :rtype: frozenset of :class:`Device` """ raise NotImplementedError() @classmethod def setup(cls, context): """ A potentially expensive method that may allow an :class:`Hypothesis` to find devices more rapidly or to find a device that it would otherwise miss. :param Context context: the pyudev context """ pass @classmethod def get_devices(cls, context, value): """ Get any devices that may correspond to the given string. :param Context context: the pyudev context :param str value: the value to look for :returns: a list of devices obtained :rtype: set of :class:`Device` """ key = cls.match(value) return cls.lookup(context, key) if key is not None else frozenset() class DeviceNumberHypothesis(Hypothesis): """ Represents the hypothesis that the device is a device number. The device may be separated into major/minor number or a composite number. """ @classmethod def _match_major_minor(cls, value): """ Match the number under the assumption that it is a major,minor pair. :param str value: value to match :returns: the device number or None :rtype: int or NoneType """ major_minor_re = re.compile(r'^(?P<major>\d+)(\D+)(?P<minor>\d+)$') match = major_minor_re.match(value) return match and os.makedev( int(match.group('major')), int(match.group('minor'))) @classmethod def _match_number(cls, value): """ Match the number under the assumption that it is a single number. :param str value: value to match :returns: the device number or None :rtype: int or NoneType """ number_re = re.compile(r'^(?P<number>\d+)$') match = number_re.match(value) return match and int(match.group('number')) @classmethod def match(cls, value): """ Match the number under the assumption that it is a device number. :returns: the device number or None :rtype: int or NoneType """ return cls._match_major_minor(value) or cls._match_number(value) @classmethod def find_subsystems(cls, context): """ Find subsystems in /sys/dev. :param Context context: the context :returns: a lis of available subsystems :rtype: list of str """ sys_path = context.sys_path return os.listdir(os.path.join(sys_path, 'dev')) @classmethod def lookup(cls, context, key): """ Lookup by the device number. :param Context context: the context :param int key: the device number :returns: a list of matching devices :rtype: frozenset of :class:`Device` """ func = wrap_exception(Devices.from_device_number) res = (func(context, s, key) for s in cls.find_subsystems(context)) return frozenset(r for r in res if r is not None) class DevicePathHypothesis(Hypothesis): """ Discover the device assuming the identifier is a device path. """ @classmethod def match(cls, value): """ Match ``value`` under the assumption that it is a device path. :returns: the device path or None :rtype: str or NoneType """ return value @classmethod def lookup(cls, context, key): """ Lookup by the path. :param Context context: the context :param str key: the device path :returns: a list of matching devices :rtype: frozenset of :class:`Device` """ res = wrap_exception(Devices.from_path)(context, key) return frozenset((res, )) if res is not None else frozenset() class DeviceNameHypothesis(Hypothesis): """ Discover the device assuming the input is a device name. Try every available subsystem. """ @classmethod def find_subsystems(cls, context): """ Find all subsystems in sysfs. :param Context context: the context :rtype: frozenset :returns: subsystems in sysfs """ sys_path = context.sys_path dirnames = ('bus', 'class', 'subsystem') absnames = (os.path.join(sys_path, name) for name in dirnames) realnames = (d for d in absnames if os.path.isdir(d)) return frozenset(n for d in realnames for n in os.listdir(d)) @classmethod def match(cls, value): """ Match ``value`` under the assumption that it is a device name. :returns: the device path or None :rtype: str or NoneType """ return value @classmethod def lookup(cls, context, key): """ Lookup by the path. :param Context context: the context :param str key: the device path :returns: a list of matching devices :rtype: frozenset of :class:`Device` """ func = wrap_exception(Devices.from_name) res = (func(context, s, key) for s in cls.find_subsystems(context)) return frozenset(r for r in res if r is not None) class DeviceFileHypothesis(Hypothesis): """ Discover the device assuming the value is some portion of a device file. The device file may be a link to a device node. """ _LINK_DIRS = [ '/dev', '/dev/disk/by-id', '/dev/disk/by-label', '/dev/disk/by-partlabel', '/dev/disk/by-partuuid', '/dev/disk/by-path', '/dev/disk/by-uuid', '/dev/input/by-path', '/dev/mapper', '/dev/md', '/dev/vg' ] @classmethod def get_link_dirs(cls, context): """ Get all directories that may contain links to device nodes. This method checks the device links of every device, so it is very expensive. :param Context context: the context :returns: a sorted list of directories that contain device links :rtype: list """ devices = context.list_devices() devices_with_links = (d for d in devices if list(d.device_links)) links = (l for d in devices_with_links for l in d.device_links) return sorted(set(os.path.dirname(l) for l in links)) @classmethod def setup(cls, context): """ Set the link directories to be used when discovering by file. Uses `get_link_dirs`, so is as expensive as it is. :param Context context: the context """ cls._LINK_DIRS = cls.get_link_dirs(context) @classmethod def match(cls, value): return value @classmethod def lookup(cls, context, key): """ Lookup the device under the assumption that the key is part of the name of a device file. :param Context context: the context :param str key: a portion of the device file name It is assumed that either it is the whole name of the device file or it is the basename. A device file may be a device node or a device link. """ func = wrap_exception(Devices.from_device_file) if '/' in key: device = func(context, key) return frozenset((device, )) if device is not None else frozenset() files = (os.path.join(ld, key) for ld in cls._LINK_DIRS) devices = (func(context, f) for f in files) return frozenset(d for d in devices if d is not None) class Discovery(object): # pylint: disable=too-few-public-methods """ Provides discovery methods for devices. """ _HYPOTHESES = [ DeviceFileHypothesis, DeviceNameHypothesis, DeviceNumberHypothesis, DevicePathHypothesis ] def __init__(self): self._hypotheses = self._HYPOTHESES def setup(self, context): """ Set up individual hypotheses. May be an expensive call. :param Context context: the context """ for hyp in self._hypotheses: hyp.setup(context) def get_devices(self, context, value): """ Get the devices corresponding to value. :param Context context: the context :param str value: some identifier of the device :returns: a list of corresponding devices :rtype: frozenset of :class:`Device` """ return frozenset( d for h in self._hypotheses for d in h.get_devices(context, value))