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: Any, mount_point: str, *, readonly: bool = False) → None

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.mount() → List[Tuple[Any, str]]

With no arguments to mount(), return a list of tuples representing all active mountpoints.

The returned list has the form [(fsobj, mount_point), …].

vfs.umount(mount_point: str | Any) → None

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: AbstractBlockDev)

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: AbstractBlockDev) → None

Build a FAT filesystem on block_dev.

class vfs.VfsRom(buffer: bytes | bytearray | memoryview)

Create a filesystem object that uses the ROMFS read-only filesystem format. buffer must be an object supporting the buffer protocol (bytes, bytearray or memoryview) that contains a valid ROMFS image.

Objects created by this constructor can be mounted using mount().

See Working with ROMFS for full details, including how to build and deploy ROMFS images with mpremote.

vfs.rom_ioctl(op: int, *args: Any) → Any

Low-level interface for accessing the read-only memory (ROM) partition(s) of the device. The supported operations are:

Call	Behaviour
rom_ioctl(1)	Return the number of available ROM partitions.
rom_ioctl(2, id)	Return partition id as a memoryview.
rom_ioctl(3, id, length)	Erase the first length bytes of partition id in preparation for writing. Returns the minimum write alignment in bytes.
rom_ioctl(4, id, offset, buf)	Write buf to partition id at byte offset.
rom_ioctl(5, id)	Finalise a write sequence to partition id (flushes caches, etc.).

These operations are normally invoked indirectly by mpremote when deploying a ROMFS image; most applications do not need to call them directly.

class vfs.VfsPosix(root: str | None = 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.

Note

VfsPosix is only available on the MicroPython Unix port; it is not present in OpenMV Cam firmware.

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 require more control over write operations – for example, writing to sub-block regions without erasing – and need the block device to support the extended interface.

class vfs.AbstractBlockDev

Documentation template for the block-device protocol. MicroPython does not actually expose this class — it is shown here only to document the methods a user-defined block-device class must implement. Constructor arguments are entirely up to the implementation (typically things like flash bus, chip-select pin, sector size, etc.).

readblocks(block_num: int, buf: bytearray) → None

readblocks(block_num: int, buf: bytearray, offset: int) → None

Read bytes from the device into buf. Two overloads expose the simple and extended interfaces.

Simple form (readblocks(block_num, buf)): reads whole blocks starting at block index block_num. len(buf) must be a multiple of the block size, and the number of blocks read is len(buf) // block_size.

Extended form (readblocks(block_num, buf, offset)): reads len(buf) bytes – not necessarily a whole number of blocks – starting at byte offset within block block_num. Use this form when the filesystem needs sub-block read access.

writeblocks(block_num: int, buf: bytes) → None

writeblocks(block_num: int, buf: bytes, offset: int) → None

Write bytes from buf to the device.

Simple form (writeblocks(block_num, buf)): writes whole blocks starting at block index block_num. len(buf) must be a multiple of the block size, and the number of blocks written is len(buf) // block_size. The implementation is responsible for erasing each destination block first if the underlying hardware requires it.

Extended form (writeblocks(block_num, buf, offset)): writes len(buf) bytes – not necessarily a whole number of blocks – starting at byte offset within block block_num. Only the bytes being written may change; the caller is responsible for ensuring affected blocks have been erased via a prior ioctl(6, block_num) call. Implementations of this form must never implicitly erase a block, even when offset is zero.

ioctl(op: int, arg: int) → int | None

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; filesystems that use the extended interface additionally require ioctl(6, ...). The need for the other operations is hardware-dependent.

Before any call to writeblocks(block, ...) a filesystem that uses the extended interface issues ioctl(6, block) so the driver can erase the block first if the hardware requires it. A driver may instead intercept ioctl(6, block) and return 0 (success), taking on the responsibility for detecting when erasure is needed itself.

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.