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:

quoted

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