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.
In writing the initial allocator, I ran into the rather
difficult problem of trying to iterate through the entire
filesystem cheaply and with only constant memory consumption
(which prohibits recursive functions).
The solution was to simply thread all directory blocks onto a
massive linked-list that spans the entire filesystem.
With the linked-list it was easy to create a traverse function
for all blocks in use on the filesystem (which has potential
for other utility), and add the rudimentary block allocator
using a bit-vector.
While the linked-list may add complexity (especially where
needing to maintain atomic operations), the linked-list helps
simplify what is currently the most expensive operation in
the filesystem, with no cost to space (the linked-list can
reuse the pointers used for chained directory blocks).
