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Re: [Qemu-devel] vmbus bridge: machine property or device?
From: |
Roman Kagan |
Subject: |
Re: [Qemu-devel] vmbus bridge: machine property or device? |
Date: |
Thu, 13 Apr 2017 17:08:04 +0300 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Wed, Apr 12, 2017 at 05:18:51PM +0200, Markus Armbruster wrote:
> Roman Kagan <address@hidden> writes:
> > VMBus is provided by a vmbus bridge; it appears the most natural to have
> > it subclassed from SysBusDevice. There can only be one VMBus in the
> > VM.
>
> TYPE_DEVICE unless you actually need something TYPE_SYS_BUS_DEVICE
> provides.
I thought VMBus looked similar to an ISA or PCI bus in its relation to
the system, and those bridges were TYPE_SYS_BUS_DEVICE.
If it's subclassed directly from TYPE_DEVICE how is it connected to the
rest of the QOM tree?
> > Now the question is how to add it to the system:
> >
> > 1) with a boolean machine property "vmbus" that would trigger the
> > creation of the VMBus bridge; its class would have
> > ->cannot_instantiate_with_device_add_yet = true
>
> This makes it an optional onboard device. Similar ones exist already,
> e.g. various optional onboard USB host controllers controlled by machine
> property "usb".
>
> > 2) with a regular -device option; this would require setting
> > ->has_dynamic_sysbus = true for i440fx machines (q35 already have it)
>
> This makes it a pluggable sysbus device.
VMBus can't be hot-plugged into the system. Besides, there can be no
more than one VMBus in the system, so multiple -device vmbus-bridge
options would not be allowed; I thought this semantics was clearer with
a machine option.
> I'd be tempted to leave old i400FX rot in peace, but your use case may
> not allow that.
It doesn't ;) Besides, we've had no specal cases for i440fx vs q35 in
our VMBus code so far, so I don't see any reason to not to support both.
Thanks,
Roman.
- [Qemu-devel] vmbus bridge: machine property or device?, Roman Kagan, 2017/04/11
- Re: [Qemu-devel] vmbus bridge: machine property or device?, Markus Armbruster, 2017/04/12
- Re: [Qemu-devel] vmbus bridge: machine property or device?, Eduardo Habkost, 2017/04/12
- Re: [Qemu-devel] vmbus bridge: machine property or device?, Roman Kagan, 2017/04/13
- Re: [Qemu-devel] vmbus bridge: machine property or device?, Eduardo Habkost, 2017/04/13
- Re: [Qemu-devel] vmbus bridge: machine property or device?, Peter Maydell, 2017/04/13
- Re: [Qemu-devel] vmbus bridge: machine property or device?, Eduardo Habkost, 2017/04/13
- Re: [Qemu-devel] vmbus bridge: machine property or device?, Peter Maydell, 2017/04/13
- Re: [Qemu-devel] vmbus bridge: machine property or device?, Roman Kagan, 2017/04/13
- Re: [Qemu-devel] vmbus bridge: machine property or device?, Roman Kagan, 2017/04/13
Re: [Qemu-devel] vmbus bridge: machine property or device?,
Roman Kagan <=