netdev - Re: [PATCH v5 0/2] Make neighbor eviction controllable by userspace

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Date:   Thu, 21 Oct 2021 14:59:09 -0700
From:   James Prestwood <prestwoj@...il.com>
To:     David Ahern <dsahern@...il.com>, netdev@...r.kernel.org
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Roopa Prabhu <roopa@...dia.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Ido Schimmel <idosch@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Chinmay Agarwal <chinagar@...eaurora.org>,
        Yajun Deng <yajun.deng@...ux.dev>,
        Tong Zhu <zhutong@...zon.com>,
        Johannes Berg <johannes@...solutions.net>,
        Jouni Malinen <jouni@...eaurora.org>
Subject: Re: [PATCH v5 0/2] Make neighbor eviction controllable by userspace

Hi David,

On Wed, 2021-10-20 at 20:33 -0600, David Ahern wrote:
> On 10/20/21 6:32 PM, James Prestwood wrote:
> > v1 -> v2:
> > 
> >  - It was suggested by Daniel Borkmann to extend the neighbor table
> > settings
> >    rather than adding IPv4/IPv6 options for ARP/NDISC separately. I
> > agree
> >    this way is much more concise since there is now only one place
> > where the
> >    option is checked and defined.
> >  - Moved documentation/code into the same patch
> >  - Explained in more detail the test scenario and results
> > 
> > v2 -> v3:
> > 
> >  - Renamed 'skip_perm' to 'nocarrier'. The way this parameter is
> > used
> >    matches this naming.
> >  - Changed logic to still flush if 'nocarrier' is false.
> > 
> > v3 -> v4:
> > 
> >  - Moved NDTPA_EVICT_NOCARRIER after NDTPA_PAD
> > 
> > v4 -> v5:
> > 
> >  - Went back to the original v1 patchset and changed:
> >  - Used ANDCONF for IN_DEV macro
> >  - Got RCU lock prior to __in_dev_get_rcu(). Do note that the logic
> >    here was extended to handle if __in_dev_get_rcu() fails. If this
> >    happens the existing behavior should be maintained and set the
> >    carrier down. I'm unsure if get_rcu() can fail in this context
> >    though. Similar logic was used for in6_dev_get.
> >  - Changed ndisc_evict_nocarrier to use a u8, proper handler, and
> >    set min/max values.
> > 
> 
> I'll take a deep dive on the patches tomorrow.
> 
> You need to add a selftests script under tools/testing/selftests/net
> that shows this behavior with the new setting set and unset. This is
> easily done with veth pairs and network namespaces (one end of the
> veth
> pair down sets the other into no-carrier). Take a look at the scripts
> there - e.g., fib_nexthops.sh should provide a template for a start
> point.

So the test itself is pretty simple. The part I'm unsure about is how
you actually set the carrier state from userspace. I see "ip link set
<dev> carrier {on,off}" but this reports not supported for veths,
wlans, and eth interfaces I have tried. AFAIK the driver controls the
carrier state. Maybe some drivers do support this?

Is there a way to set the carrier state that you, or anyone is aware
of?

Thanks,
James