Re: [PATCH] Add sk_mark route lookup support for IPv4 listening sockets, and for IPv4 multicast forwarding

[steve@chygwyn.com]

Hi,

On Wed, Oct 14, 2009 at 02:50:47AM -0700, Maciej Żenczykowski wrote:
> Problem is the primary purpose of the mark is to enable matching on
> the mark in the routing tables.
> 
> See 'ip rule  ... fwmark X ...'
> 
> ie. that fails due to circular dependency.
> 
>
I don't agree. There are two route lookups with a tunnel, the
internal one and the tunnel one. Here is an example of what I'm
thinking:

1. Look up a route which points at a remote ip addres via a tunnel device.
   The "setmark" on this route sets the skb mark
2. Look up a route on the tunnel itself (i.e. the tunnel endpoint not
   the socket endpoint) using the mark from the initial lookup. This
   route can depend on the previous lookup (if there are multiple
   routes for multiple marks) and also set the mark to use.

The default would be to inherit the mark over a route lookup, in
case that no "setmark" had been specified for that route. In
other words, it would be the same as it is now.

The mark is supposed to be a generic thing, not just for routing
lookups, it can be used for classification, etc as well. I would
expect to see such a thing used for maybe specifying a VLAN or
a reference to an MPLS label stack, or something similar too,

Steve.