On Mon, Jun 11, 2012 at 10:42 PM, Stefan Hajnoczi <stefa...@gmail.com> wrote: > On Mon, Jun 11, 2012 at 3:24 PM, Zhi Yong Wu <zwu.ker...@gmail.com> wrote: >> On Mon, Jun 11, 2012 at 4:57 PM, Stefan Hajnoczi >> <stefa...@linux.vnet.ibm.com> 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. > > When users upgrade QEMU versions and find their setup is now broken > QEMU's reputation will be damaged. You can't build critical systems > on top of software which keeps changing and breaking. Fixing it after > a user hits the problem is not okay, users won't trust us if we do > that. OK, i will try to work on this. > > We need to be disciplined when it comes to backwards compatibility. > Either we support the "VLAN" feature or we drop it. We already had > this discussion in another thread, here's what Anthony had to say: > > "Dropping features is only something that should be approached lightly and > certainly not something that should be done just because you don't like a > particular bit of code." > > http://permalink.gmane.org/gmane.comp.emulators.qemu/153600 > > Stefan
-- Regards, Zhi Yong Wu
