Document behaviour of fsync-after-close
The following should be documented:
Does close()/re-open()/fsync() provide the same durability and visibility-to-other-clients guarantees as fsync()/close() does?
POSIX leaves that open; for many local file systems the answer is "yes" (but modulo bugs; even the very recent Linux v4.17 had some issues with that).
The coreutils "sync" utility now also accepts single files as arguments, and does open()+fsync(); the answer to the above question would determine wither this will work reliably on CephFS.
For more details see: https://stackoverflow.com/questions/37288453/calling-fsync2-after-close2
It would be great to know the answer for CephFS, and have it documented.