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

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH v4 06/16] net: Remove vlan qdev property
Date: Mon, 11 Jun 2012 15:49:12 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1

On 06/11/2012 01:28 AM, 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.

I have a strong opinion :-)

We shipped a version with it, so now we have to support it.


Anthony Liguori

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