I'm not on the team anymore so I don't know if they kept the tar stuff around, but it was straightforward to scan the flash for valid tar header blocks to build

I'm not on the team anymore so I don't know if they kept the tar stuff around, but it was straightforward to scan the flash for valid tar header blocks to build the allocation bitmap and then flag header blocks as invalid when files were deleted. The total number of files we needed to keep in the flash was small, so simple brute-force stuff worked fine.