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Re: [Qemu-devel] [PATCH v4 06/16] net: Remove vlan qdev property

From: Zhi Yong Wu
Subject: Re: [Qemu-devel] [PATCH v4 06/16] net: Remove vlan qdev property
Date: Mon, 11 Jun 2012 22:24:53 +0800

On Mon, Jun 11, 2012 at 4:57 PM, Stefan Hajnoczi
<address@hidden> wrote:
> On Mon, Jun 11, 2012 at 08:28:57AM +0200, Paolo Bonzini wrote:
>> Il 09/06/2012 05:04, Zhi Yong Wu ha scritto:
>> >>>> This commit looks suspicious because it removes a user-visible qdev
>> >>>> property but we're trying to preserve backward compatibility.  This
>> >>>> command-line will break:
>> >>>>
>> >>>> x86_64-softmmu/qemu-system-x86_64 -net user,vlan=1 -device 
>> >>>> virtio-net-pci,vlan=1
>> >>>>
>> >>>> Instead of dropping the qdev_prop_vlan completely the
>> >>>> hw/qdev-properties.c code needs to call net/hub.h external functions
>> >>>> to implement equivalent functionality:
>> >>>>
>> >>>> 1. Setting the vlan=<id> property looks up the hub port and assigns
>> >>>> the NICConf->peer field.
>> >>>> 2. Getting the vlan property looks up the hub id (i.e. vlan id) given
>> >>>> the peer.  If the peer is not a hub port the result is -1.
>> >>>>
>> >>>> When I wrote this patch I missed the big picture and forgot about
>> >>>> backwards compatibility :(.
>> >>>>
>> > To be honest, i am concerned if anyone uses this syntax. Since the
>> > feature will finally be discarded, i suggest that we don't support
>> > this now. If someone complains this later, we can fix it. If nobody
>> > complains, that is what we hope.
>> I think you're missing the big picture of this series, which is exactly
>> _not_ to discard the VLAN feature, but just to rewrite it in a better way.
>> That said, I agree that this is a somewhat fringe usage; most people
>> will use -net nic,model=virtio,vlan=1 rather than "-device".  We may get
>> by with dropping it.  I have no strong opinion either way.
> Either we keep backwards compatibility or we don't.  Taking a middle
> path where we preserve only some of the "VLAN" syntax is confusing and
> inconsistent.
in terms of technology, i fully agree with you, but in terms of
usefulness and our business, it will waste our effort, time and is
meaningless if nobody or no customers use this syntax. As i said, if
someone complain this later, we can fix it.

> Like Paolo said, the point here is not to drop "VLAN" support.  We're
> simply moving this feature into a regular net client (the hub) so that
> the special case "VLAN" code in net.c can be removed.
> Stefan


Zhi Yong Wu

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