This is needed if you chdir to a ROMFS and want to query your current
directory.
Prior to this change, using `os.getcwd()` when in a ROMFS would raise:
AttributeError: 'VfsRom' object has no attribute 'getcwd'
Signed-off-by: Damien George <damien@micropython.org>
Testing with ROMFS shows that it is relatively easy to end up with a
corrupt filesystem on the device -- eg due to the ROMFS deploy process
stopping half way through -- which could lead to hard crashes. Notably,
there can be boot loops trying to mount a corrupt filesystem, crashes when
importing modules like `os` that first scan the filesystem for `os.py`, and
crashing when deploying a new ROMFS in certain cases because the old one is
removed while still mounted.
The main problem is that `mp_decode_uint()` has an loop that keeps going as
long as it reads 0xff byte values, which can happen in the case of erased
and unwritten flash.
This commit adds full bounds checking in the new `mp_decode_uint_checked()`
function, and that makes all ROMFS filesystem accesses robust.
Signed-off-by: Damien George <damien@micropython.org>
It's not necessary to support this, which allows an arbitrary memory
address to be specified and potentially allows invalid memory accesses.
Requiring an object with the buffer protocol is safer, and also means that
the length of the region is always specified.
Signed-off-by: Damien George <damien@micropython.org>
This commit defines a new ROMFS filesystem for storing read-only files that
can be memory mapped, and a new VfsRom driver. Files opened from this
filesystem support the buffer protocol. This allows naturally getting the
memory-mapped address of the file using:
- memoryview(file)
- uctypes.addressof(file)
Furthermore, if these files are .mpy files then their content can be
referenced in-place when importing. Such imports take up a lot less RAM
than importing from a normal filesystem. This is essentially dynamically
frozen .mpy files, building on the revamped v6 .mpy file format.
Signed-off-by: Damien George <damien@micropython.org>
