Re: [Qemu-devel] [PATCH qemu v2] tap: Allow specifying a bridge

[Jason Wang <jasowang@redhat.com>]

On 2016年09月19日 19:59, Paolo Bonzini wrote:
>
> On 19/09/2016 02:33, Alexey Kardashevskiy wrote:
>> On 15/09/16 07:04, Paolo Bonzini wrote:
>>>
>>> On 13/09/2016 09:11, Alexey Kardashevskiy wrote:
>>>> The tap backend is already using qemu-bridge-helper to attach tap
>>>> interface to a bridge but (unlike the bridge backend) it always uses
>>>> the default bridge name - br0.
>>>>
>>>> This adds a "br" property support to the tap backend.
>>>>
>>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>>> Stupid question ahead: how does -netdev bridge compare to -netdev tap
>>> after this patch?  Is there a case left where you must use -netdev bridge?
>>>
>>> Or can we make -netdev bridge a synonym for "-netdev
>>> tap,helper=/default/path/to/helper"?
>> I looked through history but I could not understand why "bridge" was
>> introduced in the first place as even there (a7c36ee4920ea) is an example of
>>
>> -netdev tap,helper="/usr/local/libexec/qemu-bridge-helper --br=qemubr0",id=hn0
>>
>> so it was assumed even then that people might want tap on a specific bridge.
>>
>> So my stupid question is - what do I have to do to get this accepted
>> (besides a note that it is 2.8+) or it is not interesting to anyone? :)
> I think the patch is even more interesting because it lets us simplify
> the code for -netdev bridge.
>
> Paolo
>

According to http://wiki.qemu.org/Features-Done/HelperNetworking. Looks 
like this allows creating a third party backend without modifying qemu. 
And the bridge helper is an example for this.