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136 lines
4.9 KiB
136 lines
4.9 KiB
# Public API
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''' Base filesystem classes and registration facilities '''
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class Filesystem:
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''' Base filsystem class inherited by each filesystem implementation '''
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def __init__(self, name, props, **kwprops):
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# Set common properties
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self._name = name
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# Process arguments to extract all properties
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props = _process_args(props, kwprops)
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# Delegate further initialisation to the subclass
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self.initialise(props)
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def initialise(self, props):
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''' Perform initialisation. This method is called in the constructor
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once the property arguments have been processed and merged into a
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single property dictionary. Subclasses typically use this method for
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transforming property values and assigning them to private
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attributes on the Filesystem object. '''
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async def snapshots(self):
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''' Retrieve an {ordinal: snapshot} dictionary of the snapshots that are
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managed by this Filesystem object. '''
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async def mountpoint(self):
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''' Retrieve the mountpoint path this Filesystem object is managing. '''
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@classmethod
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async def filesystems(cls):
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''' Retrieve a {name: filesystem} dictionary of the mounted filesystems
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that are managed by this Filesystem class. '''
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raise NotImplementedError()
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@classmethod
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async def expose(cls):
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''' Retrieve an object to be exposed on the global scope of the
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configuration file. The identifier of this object will equal the
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registered name of the filesystem. This may be used to expose
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variables and methods that the user will need in order to configure
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the filesystem. The method is called whenever the configuration
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file is reloaded. '''
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class Snapshot:
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''' Base snapshot class inherited by each filesystem implementation '''
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def __init__(self, filesystem, tag, props, **kwprops):
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# pylint: disable=unused-argument
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# Set common properties
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self._filesystem = filesystem
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self._tag = tag
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# Process arguments to extract all properties
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props = _process_args(props, kwprops)
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# Delegate further initialisation to the subclass
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self.initialise(props)
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def initialise(self, props):
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''' Perform initialisation. This method is called in the constructor
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once the property arguments have been processed and merged into a
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single property dictionary. Subclasses typically use this method for
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transforming property values and assigning them to private
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attributes on the Snapshot object. '''
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def filesystem(self):
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''' Get parent Filesystem object. This method need not be overridden
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in subclasses. '''
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return self._filesystem
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def tag(self):
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''' Get tag name. Each configured schedule in ZAFS has a unique tag
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name. The tag name is passed in the constructor of the snapshot. A
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tag name paired with an ordinal uniquely identifies a snapshot. This
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method need not be overridden in subclasses. '''
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return self._tag
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def ordinal(self):
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''' Get ordinal. Ordinals are sortable, hashable timestamps that are
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unique per tag name. They need not be numbers, but they must sort
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in a strictly ascending chronological order. The ordinal is
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typically derived from the UNIX timestamp the snapshot was taken at.
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Before the snapshot is taken, this method returns None. '''
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raise NotImplementedError()
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async def take(self):
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''' Take snapshot and return the ordinal. This method is never called
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more than once per snapshot object. '''
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def taken(self):
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''' This method returns True if the snapshot has been taken. '''
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async def delete(self):
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''' Delete this snapshot. No further method calls are made on the
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snapshot once it has been destroyed. '''
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class FilesystemRegistry:
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''' Class that keeps a global registry of available Filesystem classes '''
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_filesystems = {}
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@classmethod
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def register(cls, name, klass):
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''' Register a filesystem. If a filesystem needs to be configured by the
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user, it must retrieve its configuration from a dictionary at
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config['filesystems'][name]. '''
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cls._filesystems[name] = klass
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@classmethod
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def all(cls):
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''' Retrieve a {name: class} dictionary of all registered
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filesystems '''
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return dict(cls._filesystems)
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#
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# Private objects
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_filesystems = {}
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def _process_args(props, kwprops):
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''' Merge 'props' and 'kwprops' into single dictionary '''
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if props:
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if not isinstance(props, dict):
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raise TypeError('Properties argument is not a dictionary')
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props = dict(props)
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else:
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props = {}
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# Update properties dictionary with keyword arguments
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props.update(kwprops)
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return props |