The support has two parts. First, a VFS plugin now gets passed an
I/O-response handler callback on construction, which informs users of the
VFS that an I/O event occurred. This enables, for example, the libC to
check if blocking read can be completed. Further, the VFS file I/O
interface provides now functions for suspendable reads, i.e.,
queue_read() and complete_read().
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082