https://stackoverflow.com/questions/21565865/filesystem-test-suites
https://github.com/billziss-gh/secfs.test
at some point we need to actually hold inodes open when we're using them, which means storing in-use records in FDB. applying every increment/decrement to FDB is unnecessary. we should track it internally and just change FDB when we go from 0 to not-0. that means we'll need an in-memory dictionary from fuse_ino_t to counts.
- http://concurrencykit.org/ looks reasonable, brings along other valuable things, and is available as a debian package/shared library