Re: [PATCH] netlink: Fix selection of template interface

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 2737 bytes --]

On Wed, Mar 20, 2024 at 12:34:54PM +0100, Paul Holzinger wrote:
> 
> On 20/03/2024 12:02, Stefano Brivio wrote:
> > On Wed, 20 Mar 2024 11:51:59 +0100
> > Paul Holzinger <pholzing@redhat.com> wrote:
[snip]
> > > > +	if (anyifi) {
> > > > +		if (nany == 1)
> > > > +			return anyifi;
> > > > +
> > > > +		warn("Multiple interfaces with %s routes, use -i to select one",
> > > > +		     af == AF_INET ? "IPv4" : "IPv6");
> > > This should not be a warning, for me this always triggers because I have
> > > two interfaces with link local addresses and no global ipv6 route as I
> > > do not have any ipv6 connection.
> > I was about to reply as I just applied this with s/warn/info/ here :)
> The more I think about this I think this suggestion is just wrong. I have a
> valid ipv4 connection and no ipv6, offering me to use -i is just wrong as it
> will not help me, especially if one uses a different interface for ipv4/ipv6
> connections.

Yeah, I think you're right.  We should ignore link-local routes when
doin this scan.  Both for IPv6 and IPv4, although IPv4 link-local is
much rarer.  I'll have a look at that tomorrow, in the meantime this
is still better than what we had.

> > > Or maybe the correct fix is to never consider ipv6 link local routes for
> > > this logic? At least I cannot see the purpose of using a interface with
> > > only a link local route.
> > > 
> > > > +	}
> > > > +
> > > > +	if (!nany)
> > > > +		warn("No interfaces with %s routes", af == AF_INET ? "IPv4" : "IPv6");
> > ...and here, because if one has no IPv6 routes we would reintroduce the
> > issue we just fixed in 338b6321ac0d ("conf: No routable interface for
> > IPv4 or IPv6 is informational, not a warning").
> > 
> > I think the purpose of picking interfaces based on routes for
> > link-local destinations is for practical test setups like the one
> > described in https://github.com/containers/podman/issues/21896.
> > 
> > Functionally it doesn't make sense, but it shouldn't harm either
> > (right?).
> 
> I am not sure how the issue is related to link local addresses, for ipv6 a
> link local route must explicitly never be routed anywhere else besides the
> current interface so picking this seems incorrect as it will be unusable not
> matter what.
> 
> > 
> > > > +
> > > > +	return 0;
> > > >    }
> > > >    /**
> > > I reproduced by having a second interface and confirm this patch fixes it.
> > Thanks for checking! Let's hope that was the case in the failing test.
> > 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]