Asynchronous non-blocking I/O for libcephfs

Recently (or not so recently, it's been almost 2 years), the nfs-ganesha project implemented capability to utilize asynchronous non-blocking I/O to storage backends to prevent thread starvation. The assumption is that the backend provides non-blocking I/O with a callback mechanism to notify nfs-ganesha when the I/O is complete so that nfs-ganesha can subsequently asynchronously respond to the client indicating I/O completion. Ceph looks like it is structured to allow for such with Context objects having finish and complete methods that allow the I/O path to notify completion. In general libcephfs seems to use some form of condition variable Context to block and wait for this notification. This would be relatively easy to replace with a call back Context. However, libcephfs does use ObjectCacher and sets the block_writes_upfront flag which seems to make any writes that go through ObjectCacher to block using an internal condition variable and not utilize the onfreespace Context object (which maybe should have been named onfinish?). I'm wondering what the implication of setting block_writes_upfront to false would be for libcephs beyond needing to assure an onfreespace Context object is passed. Thanks Frank Filz