expose ff.c constants, raise them as arguments to FatFSError
introduce NotMounted and NoFilesystem as subclasses of FatFSError with
the appropriate error code set
- different approach to vector manipulation - more on the fly operations. Prepared for fully offloaded operations, BP on Trezor with constant memory.
- memory requirements reduced from (4MN + const) to (2MN + const)
- more raw methods to avoid unnecessary encoding/decoding
- chunking improved, chunk size set as a constant, changed from 64 to 32, missing pieces implemented to cover also BP 16
- proof_v8 support discontinued, old hardfork, not needed anymore
- get_exponent register clash fixed (for large vectors)
- reduced heap fragmentation by removing some temporary allocations
- hashing with len and offset to reduce heap fragmentation by creating a sliced arrays
- use to() wherever possible to avoid allocations and return of mutable private object
- global functions start with _ prefix, reduce import footprint
- use __slots__ in classes to minimize footprint
ff.c has a lazy-mounting feature, where any filesystem call will mount
the volume if it can. This messes with predictability of the mounted
state, so all (except mount/unmount/mkfs) Python functions will first
check if the fs is mounted.
Instead of having possibly multiple FatFS objects, each with its own
`fs` struct, there is one global static fs_instance. This is to match
the mode of operation of ff.c, which assumes a global list of mounts,
and all functions operate on the global based on path.
Methods of FatFS were converted to functions on the fatfs module.
fatfs.unmount() does not call ff.c's unmount, but simply invalidates
fs_instance. This is basically what ff.c would do, except without
messing with ff.c's global list of mounts.
It is possible to call `ensure_sdcard` in a way that requires only SD
card be inserted, but not necessarily formatted.
This is useful for SD-protect and possibly other use-cases where the SD
card is read-only, and "not formatted" is identical to "not containing
the right files".
