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Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of vi
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of virtio PCI devices |
Date: |
Wed, 17 Oct 2018 11:32:28 -0400 |
On Wed, Oct 17, 2018 at 12:10:04PM -0300, Eduardo Habkost wrote:
> On Wed, Oct 17, 2018 at 10:22:37AM +0100, Stefan Hajnoczi wrote:
> > On Fri, Oct 12, 2018 at 11:54:35PM -0300, Eduardo Habkost wrote:
> > > This patch adds separate device types for each of those virtio
> > > device flavors:
> > >
> > > - virtio-*-pci: the existing multi-purpose device types
> > > - Configurable using `disable-legacy` and `disable-modern`
> > > properties
> > > - Legacy driver support is automatically enabled/disabled
> > > depending on the bus where it is plugged
> > > - Supports Conventional PCI and PCI Express buses
> > > (but Conventional PCI is incompatible with
> > > disable-legacy=off)
> > > - Changes PCI vendor/device IDs at runtime
> > > - virtio-*-pci-0.9: legacy virtio device
> > > - Supports Conventional PCI buses only, because
> > > it has a PIO BAR
> > > - virtio-*-pci-1.0-transitional: virtio-1.0 device supporting legacy
> > > drivers
> > > - Supports Conventional PCI buses only, because
> > > it has a PIO BAR
> > > - virtio-*-pci-1.0: modern-only
> > > - Supports both Conventional PCI and PCI Express buses
> >
> > If new device types are being created, is it time to decouple the VIRTIO
> > PCI transport from the actual VIRTIO device (blk, net, scsi) like we
> > already have with virtio-mmio?
> >
> > -device virtio-pci-1.0,id=virtio-pci-0
> > -device virtio-blk,bus=virtio-pci-0,drive=drive0,serial=mydisk
> >
> > That way we avoid lots of boilerplate code and an explosion of new
> > device types.
>
> I don't think that would work. This would in turn make
> virtio-pci-1.0 a chameleon device that changes PCI ID depending
> on the backend device plugged to it.
>
> Also, PCI IDs are not the only information contained inside the
> virtio-pci subclasses. See all the PCI-specific +
> device-type-specific knowledge encoded inside the class_init and
> instance_init functions of each virtio-pci subclass.
I think we need to draw the line somewhere. We can't make new
classes and bother users each time there is a behaviour
change in the device.
But I also think the transport/device split it also an internal virtio
thing, no one who has not read the spec cares about it.
> --
> Eduardo
- Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of virtio PCI devices, (continued)
- Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of virtio PCI devices, Michael S. Tsirkin, 2018/10/15
- Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of virtio PCI devices, Eduardo Habkost, 2018/10/15
- Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of virtio PCI devices, Gerd Hoffmann, 2018/10/16
- Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of virtio PCI devices, Eduardo Habkost, 2018/10/16
- Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of virtio PCI devices, Gerd Hoffmann, 2018/10/16
- [Qemu-devel] "no-user" for properties (was: [PATCH] virtio: Provide version-specific variants of virtio PCI devices), Markus Armbruster, 2018/10/17
Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of virtio PCI devices, Cornelia Huck, 2018/10/15
Re: [Qemu-devel] [PATCH] virtio: Provide version-specific variants of virtio PCI devices, Stefan Hajnoczi, 2018/10/17