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extmod/vfs_lfs: Add mtime support to littlefs files.

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This commit adds support for modification time of files on littlefs v2
filesystems, using file attributes.  For some background see issue #6114.

Features/properties of this implementation:
- Only supported on littlefs2 (not littlefs1).
- Uses littlefs2's general file attributes to store the timestamp.
- The timestamp is 64-bits and stores nanoseconds since 1970/1/1 (if the
  range to the year 2554 is not enough then additional bits can be added to
  this timestamp by adding another file attribute).
- mtime is enabled by default but can be disabled in the constructor, eg:
  uos.mount(uos.VfsLfs2(bdev, mtime=False), '/flash')
- It's fully backwards compatible, existing littlefs2 filesystems will work
  without reformatting and timestamps will be added transparently to
  existing files (once they are opened for writing).
- Files without timestamps will open correctly, and stat will just return 0
  for their timestamp.
- mtime can be disabled or enabled each mount time and timestamps will only
  be updated if mtime is enabled (otherwise they will be untouched).

Signed-off-by: Damien George <damien@micropython.org>
This commit is contained in:
Damien George
2020-07-29 01:01:48 +10:00
parent ee50a6effe
commit 2acc087880
8 changed files with 197 additions and 23 deletions
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16
docs/library/uos.rst
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@@ -178,7 +178,7 @@ represented by VFS classes.
Build a FAT filesystem on *block_dev*.
.. class:: VfsLfs1(block_dev)
.. class:: 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
@@ -187,23 +187,31 @@ represented by VFS classes.
See :ref:`filesystem` for more information.
.. staticmethod:: mkfs(block_dev)
.. staticmethod:: 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:: VfsLfs2(block_dev)
.. class:: 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 :ref:`extended interface <block-device-interface>`.
Objects created by this constructor can be mounted using :func:`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 `uos.stat` on files without timestamps will return 0 for the timestamp.
See :ref:`filesystem` for more information.
.. staticmethod:: mkfs(block_dev)
.. staticmethod:: mkfs(block_dev, readsize=32, progsize=32, lookahead=32)
Build a Lfs2 filesystem on *block_dev*.