Re: [RFC PATCH v1 1/8] vfio-ccw: Return IOINST_CC_NOT_OPERATIONAL for EIO

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 19 Nov 2019 12:23:40 +0100
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Mon, 18 Nov 2019 19:13:34 +0100
> Cornelia Huck <cohuck@redhat.com> wrote:
> 
> > > EIO is returned by vfio-ccw mediated device when the backing
> > > host subchannel is not operational anymore. So return cc=3
> > > back to the guest, rather than returning a unit check.
> > > This way the guest can take appropriate action such as
> > > issue an 'stsch'.    
> > 
> > Hnm, I'm trying to recall whether that was actually a conscious choice,
> > but I can't quite remember... the change does make sense at a glance,
> > however.  
> 
> Is EIO returned if and only if the host subchannel/device is not
> operational any more, or are there cases as well? 

Ok, I walked through the kernel code, and it seems -EIO can happen
- when we try to do I/O while in the NOT_OPER or STANDBY states... cc 3
  makes sense in those cases
- when the cp is not initialized when trying to fetch the orb... which
  is an internal vfio-ccw kernel module error

Btw., this patch only changes one of the handlers; I think you have to
change all of start/halt/clear?

[Might also be good to double-check the handling for the different
instructions.]

> Is the mapping
> (cc to condition) documented? By the QEMU code I would think that
> we already have ENODEV and EACCESS for 'not operational' -- no idea
> why we need two codes though.

-ENODEV: device gone
-EACCES: no path operational

We should be able to distinguish between the two; in the 'no path
operational' case, the device may still be accessible with a different
path mask in the request.