netdev - Re: ARP resolving for switch drivers

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Message-ID: <CAE4R7bDnrMZSsZeZmYkT8HhkXUpgnedBo8VX5iEtyJmzJ7gV5A@mail.gmail.com>
Date:	Wed, 25 Feb 2015 21:08:30 -0800
From:	Scott Feldman <sfeldma@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: ARP resolving for switch drivers

On Sat, Feb 21, 2015 at 10:28 PM, Scott Feldman <sfeldma@...il.com> wrote:
> On Sat, Feb 21, 2015 at 10:11 PM, David Miller <davem@...emloft.net> wrote:
>>
>> Scott I looked into the current state of affairs and you should
>> be able to use generic infrastructure to resolve a neighbour
>> entry and even trigger the state machine.
>>
>> For ipv4:
>>
>>         n = __ipv4_neigh_lookup(dev, ip_addr);
>>         if (!n)
>>                 n = neigh_create(&arp_tbl, &ip_addr, dev, true);
>>         if (!n)
>>                 goto error;
>>
>>         if (!(n->nud_state & NUD_VALID))
>>                 neigh_event_send(n, NULL);
>>         else
>>                 memcpy(&hw_entry->mac_addr, n->ha, dev_addr_len);
>>
>> If you have to take the neigh_event_send() path, you have to wait for
>> the notifier to be invoked.  And in the notifier you can fetch the
>> MAC address.
>
> Perfect!  I'll give this a try shortly and test and report back.
> (Trying to beat down some remaining L2 issues first).
>

David,

Just following up on this.  The code above works great, at least for
the initial nh resolution when route is installed.  I need to do some
more testing for the cases when the neigh entry goes to !NUD_VALID,
but I'm still holding a route with nhs looking for that neigh.  I
guess I need to re-trigger the above code.  Need to play around with
it.

There are two other items I had on my list for L3 from netconf:

1) Routes that overlap tables, or how to assign priority.  I'll look
at the RFC you sent for collapsing local/main tables.  For now, I used
fib_info->fib_priority for the priority in the rocker L3 table.  Maybe
that's good enough once local/main are collapsed?  But for other
tables, I'm not sure if fib_info->fib_priority will be sufficient.  I
probably need some guidance here.

2) Marking routes as "external"[1].  I added a RTAX_FEATURE_EXTERNAL
bit to be set by application (iproute2, quagga, etc) when wanting to
install route externally, for example to a switchdev switch.  Then if
application sets bit, it is the applications responsibility to handle
failure cases and rollback any lesser-prefixed routes than may have
been pushed earlier, successfully to external.  The problem I'm
running into is internal kernel routes need to be pushed to external
and I don't want to mark those as "external", but I also want those to
be install externally (to the device), if possible.

[1] "external" seems to be the label we're giving kernel objects that
get mirrored externally to a device, such as the mark we used for FDB
entries populated into the bridge's FDB by a learning device.
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