Re: [Qemu-devel] [Bug 1594239] Re: After adding more scsi disks for Aarch64 virtual machine, start the VM and got Qemu Error

[Peter Maydell <peter.maydell@linaro.org>]

On 5 July 2016 at 15:41, Tom Hanson <thomas.hanson@linaro.org> wrote:
> As noted above, virtio-scsi-pci uses a bus address as part of the
> internal ID string while virtio-scsi-device does not.
>
>   * Is this difference intentional?

Probably not.

>   * Are they intended to support different use cases? If so, what?

virtio-scsi-device is a "virtio backend" (other backends
include char, block and net devices), which plugs into a
"virtio bus". Virtio buses are provided by "virtio transports",
which can be PCI, s390 CCW, or virtio-mmio, and any particular
virtio bus has either 0 or 1 virtio backends on it.

The general idea is that this is a clean-ish separation between
the "what is this virtio device doing" and "how exactly do you
access it". virtio-scsi-pci is one of the family of virtio-*-pci
devices which combine a virtio-pci transport and a virtio-foo
backend in one convenient package -- we provide these (a) for
backward compatibility with old command lines etc from before
we made the backend/transport split and (b) for convenience
since the command lines are shorter than if you specify
the transport and backend separately manually.

(Note that a virtio-pci transport is a pci device, not a
pci bus -- it plugs into a pci bus on one and has a
virtio-bus on the other.)

thanks
-- PMM