Refactoring asynchronous I/O

[Jilles Tjoelker]

On Tue, Jan 26, 2016 at 05:39:03PM -0800, John Baldwin wrote:
> Note that binding the AIO support to a new fileop does mean that the AIO code
> now becomes mandatory (rather than optional).  We could perhaps make the
> system calls continue to be optional if people really need that, but the guts
> of the code will now need to always be in the kernel.

Enabling this by default is OK with me as long as the easy ways to get a
stuck process are at least disabled by default. Currently, a process
gets stuck forever if it has an AIO request from or to a pipe that will
never complete. An AIO daemon should not be allowed to perform an
unbounded sleep such as for a pipe (NFS server should be OK).

-- 
Jilles Tjoelker