Re: [Qemu-devel] [PATCH 2/3] net: Deprecate tap backend's parameter "helper"

[Jason Wang <jasowang@redhat.com>]

On 2019/6/18 下午1:32, Markus Armbruster wrote:
> Jason Wang <jasowang@redhat.com> writes:
>
>> On 2019/6/4 下午7:52, Markus Armbruster wrote:
>>> -netdev tap,helper=... is a useless duplicate of -netdev bridge.
>>> Deprecate and de-document.
>>>
>>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>>
>> This requires more thought as TAP could be used independently. Force
>> using a "bridge" backend may lead some confusion.
> Can you explain your qualms in a bit more detail?
>
> The thoughts that led to this patch:
> https://lists.gnu.org/archive/html/qemu-devel/2019-05/msg03164.html
>
> Consensus back then:
>
> 1. Add qemu-bridge-helper.c to Jason's "Network device backends"
>
> 2. Deprecate -netdev tap parameter "helper"


The problem comes from this point. The main reason is TAP could be used 
without bridge e.g:

- you can simply assign an IP and and properly configure route table on 
host to make it work

- or setup tc actions or using XDP to transfer packets between TAP and 
another interfaces

- using AF_PACKET or other socket to capture the traffic and do the 
forwarding in userspace

So it looks to me switching to use -netdev bridge is inappropriate.

Thanks



>
> 3. Improve documentation of -netdev bridge
>
> 4. Create a manual page for qemu-bridge-helper that also covers
>     /etc/qemu/bridge.conf.
>
> 5. Fix the nutty error handling in parse_acl_file()
>
> This series covers the first two [PATCH 1+2], and records the remaining
> three more permanently [PATCH 3].
>