Discussion
Perhaps the bulk of SdFat.h's implementation of Microsoft's FAT filesystem is in the appropriate Volume superclass, which for FAT32 is split between deferring to a FatFile class & its FatPartition superclass.
That FatPartition superclass has a method for allocating new runs of blocks within a preconfigured range, by wrap-around iterating over all free blocks in the allocation table until it finds a free one. It may update the lower-bound of the range to save time next time.
2/5?
There's a variant of the allocator which attempts to supply contiguous runs, thus making reads of the file faster. As well as a method for zeroing out each entry of a linkedlist within that File Allocation Table.
There's a method which wraps a cache-class in the appropriate bittwiddling depending on whether we've got a FAT32, FAT16, or FAT12 filesystem.
Then there's methods for counting up how much space is free, & another to init that cache & read in various properties.
3/5?
That caching class is shared between the backends, with methods to read a new sector whilst updating (via another method) the last one as-needed, read/write a sector with that caching, flush the cache if needed invalidating in-RAM data, & some accessers. The Partition caller dereferences offsets from within the read sector.
And... There's no much more to comment on regarding partitioning! So...
4/4 Fin for today! Tomorrow: Files/directories!
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