linux-kernel - Re: [PATCH 09/10] vfio: ccw: Suppressing the BOXED state

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Message-ID: <20180430174718.7b1e5651.cohuck@redhat.com>
Date:   Mon, 30 Apr 2018 17:47:18 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Pierre Morel <pmorel@...ux.vnet.ibm.com>
Cc:     pasic@...ux.vnet.ibm.com, bjsdjshi@...ux.vnet.ibm.com,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 09/10] vfio: ccw: Suppressing the BOXED state

On Wed, 25 Apr 2018 15:55:51 +0200
Pierre Morel <pmorel@...ux.vnet.ibm.com> wrote:

> On 25/04/2018 10:44, Cornelia Huck wrote:
> > On Thu, 19 Apr 2018 16:48:12 +0200
> > Pierre Morel <pmorel@...ux.vnet.ibm.com> wrote:
> >  
> >> VFIO_CCW_STATE_BOXED and VFIO_CCW_STATE_BUSY are the same
> >> states.
> >> Let's only keep one: VFIO_CCW_STATE_BUSY
> >>
> >> Signed-off-by: Pierre Morel <pmorel@...ux.vnet.ibm.com>
> >> ---
> >>   drivers/s390/cio/vfio_ccw_fsm.c     | 9 ---------
> >>   drivers/s390/cio/vfio_ccw_private.h | 1 -
> >>   2 files changed, 10 deletions(-)  
> > I think they were initially supposed to cover two different things:
> > - BUSY: we're currently dealing with an I/O request
> > - BOXED: the device currently won't talk to us or we won't talk to it
> >
> > It seems we never really did anything useful with BOXED; but should we?
> >  
> I do not know what.

The BUSY state is something we know that we'll get out of soon-ish
(when the I/O request has finished). We could conceivably use a timeout
and drop to the BOXED state if we don't get an answer.

I think this plays also into the reserve/release and path handling
questions. One of the more common reasons for devices to become boxed
I've seen is another system doing a reserve on a dasd.