Re: [RFC] mac80211: add extap functionality

[Felix Fietkau <nbd@openwrt.org>]

On 2016-02-18 14:36, Grzegorz Bajorski wrote:
> 2016-02-17 17:55 GMT+01:00 Felix Fietkau <nbd@openwrt.org>:
>> On 2016-02-17 12:55, Grzegorz Bajorski wrote:
>>> Client interface briding was only possible when 4addr frames were used with
>>> a 4addr/WDS aware AP. It was not possible to do it otherwise due to 3addr
>>> frame limitation.
>>>
>>> The extap logic introduces a smart MAC address masking/translation
>>> (including modyfing packets beyond SA/DA, e.g. DHCP broadcast flag is set).
>>>
>>> There are still some unsolved problems and bugs:
>>>  - due to bridge port routing and sk_buff payload sharing skb_copy() is
>>>    performed; this ideally should be reworked
>>>  - ipv6 support is still not finished
>>>  - extap is enabled by default currently; it should be configurable via
>>>    nl80211 the same way 4addr is
>>>
>>> There's also an idea to move this as a generic link driver (just like
>>> macvlan, et al) which would allow unmodified cfg80211 drivers to enjoy the
>>> extap functionality. Thoughts?
>>>
>>> Note: This changes cfg80211 file in this single patch only for reviewing
>>> convienence.
>>>
>>> This is an early draft to solicit comments on the design.
>>>
>>> Signed-off-by: Grzegorz Bajorski <grzegorz.bajorski@tieto.com>
>> You can get a lot of the same effect (sharing the same subnet between
>> hosts behind multiple interfaces and having forwarding between them)
>> without any changes to mac80211.
>>
>> OpenWrt uses a daemon called 'relayd' which I wrote some years ago. It
>> does ARP translation, DHCP packet mangling and sets up policy routing to
>> forward packets between multiple interfaces.
>>
>> You can find it here:
>> http://git.openwrt.org/?p=project/relayd.git;a=summary
>> git://git.openwrt.org/project/relayd.git
>>
>> Since you can cover the same use cases with user space code, I don't
>> think it's a good idea to put bridge emulation hacks in the kernel's
>> wireless stack.
> 
> What about performance? Quick test show that is slow ~ 100-120 mbps
> (UDP tests) and procesor is overloaded. Am I missing something? I
> would expect it to be greater. (4 x 4 antena setup VHT80)
What platform are you testing it on, and what kind of UDP test are you
running?

- Felix