Took the opportunity to make some allocator tweaks:
- Renamed lfs.free -> lfs.lookahead, it's previous name did cause some
confusion.
- Renamed lfs.free.off -> lfs.lookahead.start
- Renamed lfs.free.i -> lfs.lookahead.next
- Renamed lfs.free.ack -> lfs.lookahead.acked
- Changed bitmap from using 32-bit words to using 8-bit bytes, dropping
the alignment requirement. One of the reasons for 32-bit alignment was
an attempt at future proofing for some sort of free-list.
This never landed, and if it did, it could have been provided without
breaking backwards compatiblity via an additional config option, at a
minor RAM cost.
We never used ffs/clz instructions for this bitmap, so I don't think
using 32-bit words offers much advantage. It just creates another
potential issue for users if their lookahead buffer is unaligned.
These changes should probably also be upstreamed to the current version.
They don't depend on anything rbyd specific.
Note, at some point lfs_alloc will need to be extended to mark block tags,
etc, as in-use during traversal.
Christopher Haster
eee0e6cfa1