Re: [Qemu-devel] [PATCH 3/3] s390x/css: generate channel path initialized CRW for channel path hotplug

[Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>]

* Cornelia Huck <cohuck@redhat.com> [2017-08-01 09:24:20 +0200]:

> On Tue, 1 Aug 2017 10:29:10 +0800
> Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:
> 
> > * Cornelia Huck <cohuck@redhat.com> [2017-07-31 13:13:02 +0200]:
> > 
> > > On Mon, 31 Jul 2017 11:51:37 +0800
> > > Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:
> 
> > > > When defining a vfio-ccw device, since the real subchannel implicitly
> > > > indicates the chps it bound to, we grasp the CHPIDs from sysfs (or, with
> > > > my current work, we could even retrieve these information from a new
> > > > added MMIO region). In this case, defining some channel path devices
> > > > separately does not make sense to me.  
> > > 
> > > We might want to pass only a subset of the channel paths to guest. This
> > > can only work if we can define individual chp objects.  
> > Why would we want this?
> 
> For example, if you know that a reconfiguration is coming on soon, you
> can just exclude the paths that will go away anyway and the guest will
> never know about them. Or for preferred pathing, although that one
> fortunately seems to have died out.
> 
> Not very strong reasons to spend time on this, though.
Got it.

> 
> > 
> > We can add, for example, a "chpids" parameter for the "vfio-ccw" device
> > to limit its chpids to a subset that we want it to have? E.g.:
> > 
> > For this mdev:
> > MDEV                                  Subchan.  PIM PAM POM  CHPIDs
> > ------------------------------------------------------------------------------
> > 6dfd3ec5-e8b3-4e18-a6fe-57bc9eceb920  0.0.013f  f0  f0  ff   42434445 00000000
> > 
> > We could use this command line:
> > -device vfio-ccw,sysfsdev=$MDEV_CCW013f,devno=0.0.1234,chpids=4245000000000000
> >                                                               ^^^^
> 
> Yes, that would work, should we want that. We can probably do without for now.
> 
Let's deffer this too!

-- 
Dong Jia Shi