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327 lines
14 KiB
327 lines
14 KiB
:mod:`os` -- basic "operating system" services
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==============================================
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.. module:: os
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:synopsis: basic "operating system" services
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|see_cpython_module| :mod:`python:os`.
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The ``os`` module contains functions for filesystem access and mounting,
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terminal redirection and duplication, and the ``uname`` and ``urandom``
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functions.
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General functions
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-----------------
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.. function:: uname()
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Return a tuple (possibly a named tuple) containing information about the
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underlying machine and/or its operating system. The tuple has five fields
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in the following order, each of them being a string:
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* ``sysname`` -- the name of the underlying system
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* ``nodename`` -- the network name (can be the same as ``sysname``)
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* ``release`` -- the version of the underlying system
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* ``version`` -- the MicroPython version and build date
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* ``machine`` -- an identifier for the underlying hardware (eg board, CPU)
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.. function:: urandom(n)
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Return a bytes object with *n* random bytes. Whenever possible, it is
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generated by the hardware random number generator.
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Filesystem access
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-----------------
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.. function:: chdir(path)
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Change current directory.
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.. function:: getcwd()
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Get the current directory.
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.. function:: ilistdir([dir])
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This function returns an iterator which then yields tuples corresponding to
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the entries in the directory that it is listing. With no argument it lists the
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current directory, otherwise it lists the directory given by *dir*.
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The tuples have the form *(name, type, inode[, size])*:
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- *name* is a string (or bytes if *dir* is a bytes object) and is the name of
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the entry;
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- *type* is an integer that specifies the type of the entry, with 0x4000 for
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directories and 0x8000 for regular files;
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- *inode* is an integer corresponding to the inode of the file, and may be 0
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for filesystems that don't have such a notion.
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- Some platforms may return a 4-tuple that includes the entry's *size*. For
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file entries, *size* is an integer representing the size of the file
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or -1 if unknown. Its meaning is currently undefined for directory
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entries.
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.. function:: listdir([dir])
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With no argument, list the current directory. Otherwise list the given directory.
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.. function:: mkdir(path)
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Create a new directory.
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.. function:: remove(path)
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Remove a file.
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.. function:: rmdir(path)
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Remove a directory.
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.. function:: rename(old_path, new_path)
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Rename a file.
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.. function:: stat(path)
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Get the status of a file or directory.
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.. function:: statvfs(path)
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Get the status of a fileystem.
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Returns a tuple with the filesystem information in the following order:
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* ``f_bsize`` -- file system block size
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* ``f_frsize`` -- fragment size
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* ``f_blocks`` -- size of fs in f_frsize units
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* ``f_bfree`` -- number of free blocks
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* ``f_bavail`` -- number of free blocks for unprivileged users
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* ``f_files`` -- number of inodes
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* ``f_ffree`` -- number of free inodes
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* ``f_favail`` -- number of free inodes for unprivileged users
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* ``f_flag`` -- mount flags
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* ``f_namemax`` -- maximum filename length
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Parameters related to inodes: ``f_files``, ``f_ffree``, ``f_avail``
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and the ``f_flags`` parameter may return ``0`` as they can be unavailable
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in a port-specific implementation.
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.. function:: sync()
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Sync all filesystems.
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Terminal redirection and duplication
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------------------------------------
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.. function:: dupterm(stream_object, index=0, /)
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Duplicate or switch the MicroPython terminal (the REPL) on the given `stream`-like
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object. The *stream_object* argument must be a native stream object, or derive
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from ``io.IOBase`` and implement the ``readinto()`` and
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``write()`` methods. The stream should be in non-blocking mode and
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``readinto()`` should return ``None`` if there is no data available for reading.
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After calling this function all terminal output is repeated on this stream,
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and any input that is available on the stream is passed on to the terminal input.
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The *index* parameter should be a non-negative integer and specifies which
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duplication slot is set. A given port may implement more than one slot (slot 0
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will always be available) and in that case terminal input and output is
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duplicated on all the slots that are set.
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If ``None`` is passed as the *stream_object* then duplication is cancelled on
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the slot given by *index*.
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The function returns the previous stream-like object in the given slot.
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Filesystem mounting
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-------------------
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Some ports provide a Virtual Filesystem (VFS) and the ability to mount multiple
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"real" filesystems within this VFS. Filesystem objects can be mounted at either
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the root of the VFS, or at a subdirectory that lives in the root. This allows
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dynamic and flexible configuration of the filesystem that is seen by Python
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programs. Ports that have this functionality provide the :func:`mount` and
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:func:`umount` functions, and possibly various filesystem implementations
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represented by VFS classes.
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.. function:: mount(fsobj, mount_point, *, readonly)
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Mount the filesystem object *fsobj* at the location in the VFS given by the
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*mount_point* string. *fsobj* can be a a VFS object that has a ``mount()``
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method, or a block device. If it's a block device then the filesystem type
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is automatically detected (an exception is raised if no filesystem was
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recognised). *mount_point* may be ``'/'`` to mount *fsobj* at the root,
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or ``'/<name>'`` to mount it at a subdirectory under the root.
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If *readonly* is ``True`` then the filesystem is mounted read-only.
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During the mount process the method ``mount()`` is called on the filesystem
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object.
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Will raise ``OSError(EPERM)`` if *mount_point* is already mounted.
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.. function:: umount(mount_point)
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Unmount a filesystem. *mount_point* can be a string naming the mount location,
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or a previously-mounted filesystem object. During the unmount process the
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method ``umount()`` is called on the filesystem object.
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Will raise ``OSError(EINVAL)`` if *mount_point* is not found.
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.. class:: VfsFat(block_dev)
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Create a filesystem object that uses the FAT filesystem format. Storage of
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the FAT filesystem is provided by *block_dev*.
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Objects created by this constructor can be mounted using :func:`mount`.
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.. staticmethod:: mkfs(block_dev)
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Build a FAT filesystem on *block_dev*.
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.. class:: VfsLfs1(block_dev, readsize=32, progsize=32, lookahead=32)
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Create a filesystem object that uses the `littlefs v1 filesystem format`_.
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Storage of the littlefs filesystem is provided by *block_dev*, which must
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support the :ref:`extended interface <block-device-interface>`.
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Objects created by this constructor can be mounted using :func:`mount`.
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See :ref:`filesystem` for more information.
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.. staticmethod:: mkfs(block_dev, readsize=32, progsize=32, lookahead=32)
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Build a Lfs1 filesystem on *block_dev*.
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.. note:: There are reports of littlefs v1 failing in certain situations,
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for details see `littlefs issue 347`_.
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.. class:: VfsLfs2(block_dev, readsize=32, progsize=32, lookahead=32, mtime=True)
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Create a filesystem object that uses the `littlefs v2 filesystem format`_.
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Storage of the littlefs filesystem is provided by *block_dev*, which must
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support the :ref:`extended interface <block-device-interface>`.
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Objects created by this constructor can be mounted using :func:`mount`.
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The *mtime* argument enables modification timestamps for files, stored using
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littlefs attributes. This option can be disabled or enabled differently each
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mount time and timestamps will only be added or updated if *mtime* is enabled,
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otherwise the timestamps will remain untouched. Littlefs v2 filesystems without
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timestamps will work without reformatting and timestamps will be added
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transparently to existing files once they are opened for writing. When *mtime*
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is enabled `os.stat` on files without timestamps will return 0 for the timestamp.
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See :ref:`filesystem` for more information.
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.. staticmethod:: mkfs(block_dev, readsize=32, progsize=32, lookahead=32)
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Build a Lfs2 filesystem on *block_dev*.
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.. note:: There are reports of littlefs v2 failing in certain situations,
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for details see `littlefs issue 295`_.
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.. _littlefs v1 filesystem format: https://github.com/ARMmbed/littlefs/tree/v1
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.. _littlefs v2 filesystem format: https://github.com/ARMmbed/littlefs
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.. _littlefs issue 295: https://github.com/ARMmbed/littlefs/issues/295
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.. _littlefs issue 347: https://github.com/ARMmbed/littlefs/issues/347
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Block devices
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-------------
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A block device is an object which implements the block protocol. This enables a
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device to support MicroPython filesystems. The physical hardware is represented
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by a user defined class. The :class:`AbstractBlockDev` class is a template for
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the design of such a class: MicroPython does not actually provide that class,
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but an actual block device class must implement the methods described below.
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A concrete implementation of this class will usually allow access to the
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memory-like functionality of a piece of hardware (like flash memory). A block
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device can be formatted to any supported filesystem and mounted using ``os``
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methods.
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See :ref:`filesystem` for example implementations of block devices using the
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two variants of the block protocol described below.
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.. _block-device-interface:
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Simple and extended interface
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.............................
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There are two compatible signatures for the ``readblocks`` and ``writeblocks``
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methods (see below), in order to support a variety of use cases. A given block
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device may implement one form or the other, or both at the same time. The second
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form (with the offset parameter) is referred to as the "extended interface".
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Some filesystems (such as littlefs) that require more control over write
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operations, for example writing to sub-block regions without erasing, may require
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that the block device supports the extended interface.
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.. class:: AbstractBlockDev(...)
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Construct a block device object. The parameters to the constructor are
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dependent on the specific block device.
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.. method:: readblocks(block_num, buf)
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readblocks(block_num, buf, offset)
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The first form reads aligned, multiples of blocks.
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Starting at the block given by the index *block_num*, read blocks from
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the device into *buf* (an array of bytes).
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The number of blocks to read is given by the length of *buf*,
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which will be a multiple of the block size.
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The second form allows reading at arbitrary locations within a block,
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and arbitrary lengths.
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Starting at block index *block_num*, and byte offset within that block
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of *offset*, read bytes from the device into *buf* (an array of bytes).
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The number of bytes to read is given by the length of *buf*.
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.. method:: writeblocks(block_num, buf)
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writeblocks(block_num, buf, offset)
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The first form writes aligned, multiples of blocks, and requires that the
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blocks that are written to be first erased (if necessary) by this method.
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Starting at the block given by the index *block_num*, write blocks from
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*buf* (an array of bytes) to the device.
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The number of blocks to write is given by the length of *buf*,
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which will be a multiple of the block size.
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The second form allows writing at arbitrary locations within a block,
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and arbitrary lengths. Only the bytes being written should be changed,
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and the caller of this method must ensure that the relevant blocks are
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erased via a prior ``ioctl`` call.
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Starting at block index *block_num*, and byte offset within that block
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of *offset*, write bytes from *buf* (an array of bytes) to the device.
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The number of bytes to write is given by the length of *buf*.
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Note that implementations must never implicitly erase blocks if the offset
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argument is specified, even if it is zero.
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.. method:: ioctl(op, arg)
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Control the block device and query its parameters. The operation to
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perform is given by *op* which is one of the following integers:
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- 1 -- initialise the device (*arg* is unused)
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- 2 -- shutdown the device (*arg* is unused)
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- 3 -- sync the device (*arg* is unused)
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- 4 -- get a count of the number of blocks, should return an integer
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(*arg* is unused)
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- 5 -- get the number of bytes in a block, should return an integer,
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or ``None`` in which case the default value of 512 is used
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(*arg* is unused)
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- 6 -- erase a block, *arg* is the block number to erase
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As a minimum ``ioctl(4, ...)`` must be intercepted; for littlefs
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``ioctl(6, ...)`` must also be intercepted. The need for others is
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hardware dependent.
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Prior to any call to ``writeblocks(block, ...)`` littlefs issues
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``ioctl(6, block)``. This enables a device driver to erase the block
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prior to a write if the hardware requires it. Alternatively a driver
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might intercept ``ioctl(6, block)`` and return 0 (success). In this case
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the driver assumes responsibility for detecting the need for erasure.
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Unless otherwise stated ``ioctl(op, arg)`` can return ``None``.
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Consequently an implementation can ignore unused values of ``op``. Where
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``op`` is intercepted, the return value for operations 4 and 5 are as
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detailed above. Other operations should return 0 on success and non-zero
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for failure, with the value returned being an ``OSError`` errno code.
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