[ewg] Re: [PATCH] link-local address fix for rdma_resolve_addr

[Jason Gunthorpe]

On Wed, Oct 21, 2009 at 04:17:01PM -0700, Sean Hefty wrote:

> This doesn't end up doing the same thing as what resolve_local did.  It only
> matches up with the 'else if' portion below: 

It does all the behaviors, it passes the input into a routing lookup
- though it is true the source needs to be passed into the routing
lookup, which I think David had in another patch. Dave; I guess you
need to include that here now.

So, first case:

> >-		if (ipv4_is_zeronet(src_ip)) {

Looks like:
$ ip route get 10.0.0.11
local 10.0.0.11 dev lo  src 10.0.0.11 
    cache <local>  mtu 16436 advmss 16396 hoplimit 64

trips through the if == loopback and does
'rdma_translate_ip(10.0.0.11)'

Same as the old code (little different path, but seems to give the
same result)

Second case:

> >-		} else if (ipv4_is_loopback(src_ip)) {

Looks like:
$ ip route get 10.0.0.11 from 127.0.0.1
local 10.0.0.11 from 127.0.0.1 dev lo 
    cache <local>  mtu 16436 advmss 16396 hoplimit 64

so trips through the if == loopback and does rdma_translate_ip(10.0.0.11)

Same as the old code

Third case:
> >-		} else {

$ ip route get 10.0.0.11 from 10.0.0.11
local 10.0.0.11 from 10.0.0.11 dev lo 
    cache <local>  mtu 16436 advmss 16396 hoplimit 64

Again, does rdma_translate_ip(10.0.0.11)

And the weird case is different:

$ ip route get 10.0.0.11 from 192.168.122.1
local 10.0.0.11 from 192.168.122.1 dev lo 
    cache <local>  mtu 16436 advmss 16396 hoplimit 64

(192.168.122.1 is bound to a different device on my system than
10.0.0.11)

The new case trips the if == loopback and does
rdma_translate_ip(10.0.0.11)

The old case does rdma_translate_ip(192.168.122.1)

I don't think this is a significant difference, both behaviors are
reasonable choices and the code/complexity savings are worth it, IMHO.
[Alternatively, I suppose one could call rdma_translate_ip(rt->rt_src)
and if that fails then do rdma_translate_ip(dst_in) but why bother?]

Jason