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vfs – virtual filesystem control

The vfs module contains functions for creating filesystem objects and mounting/unmounting them in the Virtual Filesystem.

Filesystem mounting

Some ports provide a Virtual Filesystem (VFS) and the ability to mount multiple “real” filesystems within this VFS. Filesystem objects can be mounted at either the root of the VFS, or at a subdirectory that lives in the root. This allows dynamic and flexible configuration of the filesystem that is seen by Python programs. Ports that have this functionality provide the mount() and umount() functions, and possibly various filesystem implementations represented by VFS classes.

vfs.mount(fsobj, mount_point, *, readonly)

Mount the filesystem object fsobj at the location in the VFS given by the mount_point string. fsobj can be a a VFS object that has a mount() method, or a block device. If it’s a block device then the filesystem type is automatically detected (an exception is raised if no filesystem was recognised). mount_point may be '/' to mount fsobj at the root, or '/<name>' to mount it at a subdirectory under the root.

If readonly is True then the filesystem is mounted read-only.

During the mount process the method mount() is called on the filesystem object.

Will raise OSError(EPERM) if mount_point is already mounted.

vfs.umount(mount_point)

Unmount a filesystem. mount_point can be a string naming the mount location, or a previously-mounted filesystem object. During the unmount process the method umount() is called on the filesystem object.

Will raise OSError(EINVAL) if mount_point is not found.

class vfs.VfsFat(block_dev)

Create a filesystem object that uses the FAT filesystem format. Storage of the FAT filesystem is provided by block_dev. Objects created by this constructor can be mounted using mount().

static mkfs(block_dev)

Build a FAT filesystem on block_dev.

class vfs.VfsLfs1(block_dev, readsize=32, progsize=32, lookahead=32)

Create a filesystem object that uses the littlefs v1 filesystem format. Storage of the littlefs filesystem is provided by block_dev, which must support the extended interface. Objects created by this constructor can be mounted using mount().

See Working with filesystems for more information.

static mkfs(block_dev, readsize=32, progsize=32, lookahead=32)

Build a Lfs1 filesystem on block_dev.

Note

There are reports of littlefs v1 failing in certain situations, for details see littlefs issue 347.

class vfs.VfsLfs2(block_dev, readsize=32, progsize=32, lookahead=32, mtime=True)

Create a filesystem object that uses the littlefs v2 filesystem format. Storage of the littlefs filesystem is provided by block_dev, which must support the extended interface. Objects created by this constructor can be mounted using mount().

The mtime argument enables modification timestamps for files, stored using littlefs attributes. This option can be disabled or enabled differently each mount time and timestamps will only be added or updated if mtime is enabled, otherwise the timestamps will remain untouched. Littlefs v2 filesystems without timestamps will work without reformatting and timestamps will be added transparently to existing files once they are opened for writing. When mtime is enabled os.stat on files without timestamps will return 0 for the timestamp.

See Working with filesystems for more information.

static mkfs(block_dev, readsize=32, progsize=32, lookahead=32)

Build a Lfs2 filesystem on block_dev.

Note

There are reports of littlefs v2 failing in certain situations, for details see littlefs issue 295.

class vfs.VfsPosix(root=None)

Create a filesystem object that accesses the host POSIX filesystem. If root is specified then it should be a path in the host filesystem to use as the root of the VfsPosix object. Otherwise the current directory of the host filesystem is used.

Block devices

A block device is an object which implements the block protocol. This enables a device to support MicroPython filesystems. The physical hardware is represented by a user defined class. The AbstractBlockDev class is a template for the design of such a class: MicroPython does not actually provide that class, but an actual block device class must implement the methods described below.

A concrete implementation of this class will usually allow access to the memory-like functionality of a piece of hardware (like flash memory). A block device can be formatted to any supported filesystem and mounted using os methods.

See Working with filesystems for example implementations of block devices using the two variants of the block protocol described below.

Simple and extended interface

There are two compatible signatures for the readblocks and writeblocks methods (see below), in order to support a variety of use cases. A given block device may implement one form or the other, or both at the same time. The second form (with the offset parameter) is referred to as the “extended interface”.

Some filesystems (such as littlefs) that require more control over write operations, for example writing to sub-block regions without erasing, may require that the block device supports the extended interface.

class vfs.AbstractBlockDev(...)

Construct a block device object. The parameters to the constructor are dependent on the specific block device.

readblocks(block_num, buf)

readblocks(block_num, buf, offset)

The first form reads aligned, multiples of blocks. Starting at the block given by the index block_num, read blocks from the device into buf (an array of bytes). The number of blocks to read is given by the length of buf, which will be a multiple of the block size.

The second form allows reading at arbitrary locations within a block, and arbitrary lengths. Starting at block index block_num, and byte offset within that block of offset, read bytes from the device into buf (an array of bytes). The number of bytes to read is given by the length of buf.

writeblocks(block_num, buf)

writeblocks(block_num, buf, offset)

The first form writes aligned, multiples of blocks, and requires that the blocks that are written to be first erased (if necessary) by this method. Starting at the block given by the index block_num, write blocks from buf (an array of bytes) to the device. The number of blocks to write is given by the length of buf, which will be a multiple of the block size.

The second form allows writing at arbitrary locations within a block, and arbitrary lengths. Only the bytes being written should be changed, and the caller of this method must ensure that the relevant blocks are erased via a prior ioctl call. Starting at block index block_num, and byte offset within that block of offset, write bytes from buf (an array of bytes) to the device. The number of bytes to write is given by the length of buf.

Note that implementations must never implicitly erase blocks if the offset argument is specified, even if it is zero.

ioctl(op, arg)

Control the block device and query its parameters. The operation to perform is given by op which is one of the following integers:

• 1 – initialise the device (arg is unused)

• 2 – shutdown the device (arg is unused)

• 3 – sync the device (arg is unused)

• 4 – get a count of the number of blocks, should return an integer (arg is unused)

• 5 – get the number of bytes in a block, should return an integer, or None in which case the default value of 512 is used (arg is unused)

• 6 – erase a block, arg is the block number to erase

As a minimum ioctl(4, ...) must be intercepted; for littlefs ioctl(6, ...) must also be intercepted. The need for others is hardware dependent.

Prior to any call to writeblocks(block, ...) littlefs issues ioctl(6, block). This enables a device driver to erase the block prior to a write if the hardware requires it. Alternatively a driver might intercept ioctl(6, block) and return 0 (success). In this case the driver assumes responsibility for detecting the need for erasure.

Unless otherwise stated ioctl(op, arg) can return None. Consequently an implementation can ignore unused values of op. Where op is intercepted, the return value for operations 4 and 5 are as detailed above. Other operations should return 0 on success and non-zero for failure, with the value returned being an OSError errno code.