Hi Jiri, Sorry for joining the discussion this late, but I have been without mail access for the last few days.
The 08/30/2019 08:36, Jiri Pirko wrote: > Fri, Aug 30, 2019 at 08:02:33AM CEST, da...@davemloft.net wrote: > >From: Jiri Pirko <j...@resnulli.us> > >Date: Fri, 30 Aug 2019 07:39:40 +0200 > > > >> Because the "promisc mode" would gain another meaning. Now how the > >> driver should guess which meaning the user ment when he setted it? > >> filter or trap? > >> > >> That is very confusing. If the flag is the way to do this, let's > >> introduce another flag, like IFF_TRAPPING indicating that user wants > >> exactly this. > > > >I don't understand how the meaning of promiscuous mode for a > >networking device has suddenly become ambiguous, when did this start > >happening? > > The promiscuity is a way to setup the rx filter. So promics == rx filter > off. For normal nics, where there is no hw fwd datapath, > this coincidentally means all received packets go to cpu. > But if there is hw fwd datapath, rx filter is still off, all rxed packets > are processed. But that does not mean they should be trapped to cpu. > > Simple example: > I need to see slowpath packets, for example arps/stp/bgp/... that > are going to cpu, I do: > tcpdump -i swp1 How is this different from "tcpdump -p -i swp1" > I don't want to get all the traffic running over hw running this cmd. > This is a valid usecase. > > To cope with hw fwd datapath devices, I believe that tcpdump has to have > notion of that. Something like: > > tcpdump -i swp1 --hw-trapping-mode > > The logic can be inverse: > tcpdump -i swp1 > tcpdump -i swp1 --no-hw-trapping-mode > > However, that would provide inconsistent behaviour between existing and > patched tcpdump/kernel. > > All I'm trying to say, there are 2 flags > needed (if we don't use tc trap). I have been reading through this thread several times and I still do not get it. As far as I understand you are arguing that we need 3 modes: - tcpdump -i swp1 - tcpdump -p -i swp1 - tcpdump -i swp1 --hw-trapping-mode Would you mind provide an example of the traffic you want to see in the 3 cases (or the traffic which you do not want to see). /Allan
