Re: [Qemu-devel] [PATCH v2 2/5] vfio-ccw: concurrent I/O handling

[Cornelia Huck]

On Fri, 25 Jan 2019 15:01:01 +0100
Halil Pasic <address@hidden> wrote:

> On Fri, 25 Jan 2019 13:58:35 +0100
> Cornelia Huck <address@hidden> wrote:

> > - We currently do not want the user space to submit another channel
> >   program while the first one is still in flight. As submitting another
> >   one is a valid request, however, we should allow this in the future
> >   (once we have the code to handle that in place).  
> 
> I don't agree. There is at most one channel program processed by a
> subchannel at any time. I would prefer an early error code if channel
> programs are issued on top of each other (our virtual subchannel
> is channel pending or FC start function bit set or similar).

You can submit a new request if the subchannel is pending with primary,
but not with secondary state.

Regardless of that, I think it is much easier to push as much as
possible of sorting out of requests to the hardware.