netdev - Re: [PATCH net-next 0/2] Neighbour table prep for MPLS

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Date:	Wed, 4 Mar 2015 09:56:33 -0500
From:	Andy Gospodarek <gospo@...ulusnetworks.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/2] Neighbour table prep for MPLS

On Tue, Mar 03, 2015 at 11:53:21PM -0600, Eric W. Biederman wrote:
> David Miller <davem@...emloft.net> writes:
> 
> > From: ebiederm@...ssion.com (Eric W. Biederman)
> > Date: Tue, 03 Mar 2015 17:09:35 -0600
> >
> >> In preparation for using the IPv4 and IPv6 neighbour tables in my mpls
> >> code this patchset factors out ___neigh_lookup_noref from
> >> __ipv4_neigh_lookup_noref, __ipv6_lookup_noref and neigh_lookup.
> >> Allowing the lookup logic to be shared between the different
> >> implementations.  At what appears to be no cost. (Aka the same assembly
> >> is generated for ip6_finish_output2 and ip_finish_output2).
> >> 
> >> After that I add a simple function that takes an address family and an
> >> address consults the neighbour table and sends the packet to the
> >> appropriate location.  The address family argument decoupls callers
> >> of neigh_xmit from the addresses families the packets are sent over.
> >> (Aka The ipv6 module can be loaded after mpls and a previously
> >> configured ipv6 next hop will start working).
> >> 
> >> The refactoring in ___neigh_lookup_noref may be a bit overkill but it
> >> feels like the right thing to do.  Especially since the same code is
> >> generated.
> >
> > Series applied, thanks.
> >
> > Maybe we can make neigh_table_find() faster by making it a direct
> > array demux of some kind instead of some switch statment thing?
> > It's the only think I don't like about neigh_xmit().
> 
> We could potentially translate the numbers into the enumeration that is
> NEIGH_ARP_TABLE, NEIGH_ND_TABLE, and NEIGH_DN_TABLE.  Or waste a little
> bit of memory in have a 30 entry array and looking things up by address
> protocol number.   The only disadvantage I can see to using AF_NNN as
> the index is that it might be a little less cache friendly.
> 
> Other issues the hh header cache doesn't work. (How much do we care).
> 
> I worry a little that supporting AF_PACKET case might cause problems
> in the future.
> 
> The cumulus folks are probably going to want to use neigh_xmit so they
> can have ipv6 nexthops on ipv4.  Using this for IPv4 and loosing the
> header cache worries me a little.

Agreed, this will be good.  I had done something a bit different coming
off the the discussions at netconf, but I'll rebase to this and use it
instead.  Thanks, Eric!

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