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180f3f29ab
This is a large commit, since this is essentially a complete rewrite of the key low-level functions that handle reading/writing blocks. This is, however, a necessary prerequisite of being able to write holes. The previous version of `flush_block_list()` (along with its numerous helper functions) was entirely reliant on all blocks being sequential. In contrast to the previous implementation, the new version of `flush_block_list()` simply writes out the difference between the old block list and the new block list by calculating the correct indirect block(s) to update based on the relevant block's logical index. `compute_block_list()` has also been rewritten, since the estimated amount of meta blocks was incorrectly calculated for files with holes as a result of the estimated amount of blocks being a function of the file size. Since it isn't possible to accurately compute the shape of the block list without traversing it, we no longer try to perform such a computation, and instead simply search through all of the allocated indirect blocks. `compute_block_list_with_meta_blocks()` has also been removed in favor of the new `compute_meta_blocks()`, since meta blocks are fundamentally distinct from data blocks due to there being no mapping between any logical block index and the physical block index.