This provides a limited form of wear leveling. While wear is
not actually balanced across blocks, the filesystem can recover
from corrupted blocks and extend the lifetime of a device nearly
as much as dynamic wear leveling.
For use-cases where wear is important, it would be better to use
a full form of dynamic wear-leveling at the block level. (or
consider a logging filesystem).
Corrupted block handling was simply added on top of the existing
logic in place for the filesystem, so it's a bit more noodly than
it may have to be, but it gets the work done.
Before, the lfs had multiple paths to determine config options:
- lfs_config struct passed during initialization
- lfs_bd_info struct passed during block device initialization
- compile time options
This allowed different developers to provide their own needs
to the filesystem, such as the block device capabilities and
the higher level user's own tweaks.
However, this comes with additional complexity and action required
when the configurations are incompatible.
For now, this has been reduced to all information (including block
device function pointers) being passed through the lfs_config struct.
We just defer more complicated handling of configuration options to
the top level user.
This simplifies configuration handling and gives the top level user
the responsibility to handle configuration, which they probably would
have wanted to do anyways.
After quite a bit of prototyping, settled on the following functions:
- lfs_dir_alloc - create a new dir
- lfs_dir_fetch - load and check a dir pair from disk
- lfs_dir_commit - save a dir pair to disk
- lfs_dir_shift - shrink a dir pair to disk
- lfs_dir_append - add a dir entry, creating dirs if needed
- lfs_dir_remove - remove a dir entry, dropping dirs if needed
Additionally, followed through with a few other tweaks
