There are use cases for not syncing at all; think build cache repos, etc. Let's be consistent here and make sure if fsync is disabled we do no sync at all. I chose this opportunity to add tests using the shiny new strace fault injection. I can forsee using this for a lot more things, so I made the support for detecting things generic. Related: https://github.com/ostreedev/ostree/issues/1184 Closes: #1186 Approved by: jlebon