Refactoring asynchronous I/O

[Slawa Olhovchenkov]

On Wed, Jan 27, 2016 at 09:52:12AM -0800, John Baldwin wrote:

> On Wednesday, January 27, 2016 01:52:05 PM Slawa Olhovchenkov wrote:
> > On Tue, Jan 26, 2016 at 05:39:03PM -0800, John Baldwin wrote:
> > 
> > > The original motivation for my changes is to support efficient zero-copy
> > > receive for TOE using Chelsio T4/T5 adapters.  However, read() is ill
> > 
> > I undertuns that not you work, but: what about (teoretical) async
> > open/close/unlink/etc?
> 
> Implementing more asynchronous operations is orthogonal to this.  It
> would perhaps be a bit simpler to implement these in the new model
> since most of the logic would live in a vnode-specific aio_queue
> method in vfs_vnops.c.  However, the current AIO approach is to add a
> new system call for each async system call (e.g. aio_open()).  You
> would then create an internal LIO opcode (e.g. LIO_OPEN).  The vnode
> aio hook would then have to support LIO_OPEN requests and return the
> opened fd via aio_complete().  Async stat / open might be nice for
> network filesystems in particular.  I've known of programs forking
> separate threads just to do open/fstat of NFS files to achieve the
> equivalent of aio_open() / aio_stat().

Some problem exist for open()/unlink/rename/etc -- you can't use
fd-related semantic.