Re: [Qemu-devel] Virtio refactoring.

From: Cornelia Huck <cornelia.huck@de.ibm.com>
To: "KONRAD Frédéric" <fred.konrad@greensocs.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	aliguori@us.ibm.com, Evgeny Voevodin <e.voevodin@samsung.com>,
	Mark Burton <mark.burton@greensocs.com>,
	qemu-devel@nongnu.org, agraf@suse.de
Subject: Re: [Qemu-devel] Virtio refactoring.
Date: Thu, 15 Nov 2012 13:05:35 +0100	[thread overview]
Message-ID: <20121115130535.02b034ee@BR9GNB5Z> (raw)
In-Reply-To: <50A4C4AD.9020509@greensocs.com>

On Thu, 15 Nov 2012 11:32:13 +0100
KONRAD Frédéric <fred.konrad@greensocs.com> wrote:

> For the qtree structure we have eg for virtio block :
> 
> bus: main-system-bus
>    type System
>    dev: pcihost, id ""
>      bus: pci.0
>        type PCI
>        dev: virtio-blk-pci, id ""
>          ...
> 

My current virtio-ccw layout is:

bus: main-system-bus
  type System
  dev: virtio-ccw-bridge, id ""
    bus: virtio-ccw
      type virtio-ccw-bus
      dev: virtio-blk-ccw, id ""
        ...

> And it would become :
> 
> bus: main-system-bus
>    type System
>    dev: pcihost, id ""
>      bus: pci.0
>        type PCI
>        dev: virtio-pci, id ""
>          bus: virtio.0
>            type VIRTIO
>            dev: virtio-blk, id ""
>              ...
> 

I guess we could have the following for virtio-ccw:

bus: main-system-bus
  type System
  dev: css, id ""
    bus: css.fe
      type ccw
      dev: virtio-ccw, id ""
        bus: virtio.0
          type virtio
          dev: virtio-blk, id ""
          ...

IOW, we introduce a channel subsystem (css) analogous to pcihost, have
a ccw bus which can hold all kinds of channel devices, introduce a bus
per channel subsystem image (here: the virtual css fe) and stick the
virtio bus under it. If we want to support passthrough of real channel
devices some day, they get their own bus for their channel subsystem
(css.0, css.1, ...) and have the devices show up under it.

(Just thinking aloud. I'll probably need to play with that idea a bit.)

> >
> >>>> Is it the right approach ? Do I miss something ?
> >>> What of the alias handling? Can this be killed once everything has been
> >>> converted?
> >> Which alias ?
> > The alias stuff in hw/qdev-monitor.c that lets you specify either
> > virtio-<type>-<transport> or virtio-<type>.
> >
> So it would break the alias, we must find a solution for that.

I think only virtio-xxx-pci and s390-virtio-xxx need to get backward
compatibility; virtio-mmio and virtio-ccw should not need to deal with
old interfaces.