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Date: Wed, 07 Oct 2009 13:33:57 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 3/6] virtio-console: Add a virtio-console
	bus, support for multiple ports
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To: Amit Shah <amit.shah@redhat.com>
Cc: qemu-devel@nongnu.org

On 10/07/09 12:06, Amit Shah wrote:
>> Oh, I thought it would create a new virtio-serial-bus (plus auto-created
>> port0 console) unconditionally.  Just do enougth to keep existing users
>> of the switch working.
>>
>> If you want new features (i.e. two consoles ports attached to one
>> virtio-serial-bus device) you must use the new syntax.
>
> So it's better overall to drop the old syntax altogether, right? It
> could get easily confusing otherwise.
>
> We can easily end up having:
>
> -virtioconsole<chardev>
> <auto-creates a bus and attaches a console port to it>
>
> -device virtio-serial-pci,id=blah
> <a second bus>
>
> -device virtport,bus=blah.0
>
> <and no way to connect a device to the bus that got created by
> virtioconsole>

It isn't that bad.

First, the busses get names based on the bus type by default, i.e. when 
creating a scsi adapter without specifying id=seomthing the bus is 
simply named "scsi.0".  Likewise the -virtioconsole created bus would be 
"port.0" or simliar (depends on the name in BusInfo).

Second, the bus= argument is optional.  If not specified, qdev will pick 
the first bus of a matching type it finds.  So as long you have a single 
port/scsi/usb/... bus only you don't need bus= at all.  You can do:

  -virtioconsole <chardev> -device virtport,<args>

and it will work just fine (creating a bus with the autocreated console 
and additionally a virtport device attached to the same bus).

cheers,
   Gerd