The 09/02/2019 19:51, Jiri Pirko wrote: > External E-Mail > > > Mon, Sep 02, 2019 at 07:42:31PM CEST, allan.niel...@microchip.com wrote: > >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 > > Depends on default. Promisc is on. > > > >- tcpdump -p -i swp1 > > All traffic that is trapped to the cpu by default, not promisc means > only mac of the interface (if bridge for example haven't set promisc > already) and special macs. So host traffic (ip of host), bgp, arp, nsnd, > etc.
In the case where the interface is enslaved to a bridge, it is put into promisc mode, which means that "tcpdump -i swp1" and "tcpdump -p -i swp1" give the same result, right? Is this desirable? > >- tcpdump -i swp1 --hw-trapping-mode > > Promisc is on, all traffic received on the port and pushed to cpu. User > has to be careful because in case of mlxsw this can lead to couple > hundred gigabit traffic going over limited pci bandwidth (gigabits). > > > > > >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 > > > -- /Allan
