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net/ipv6: Simplify route replace and appending into multipath route

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Bring consistency to ipv6 route replace and append semantics.

Remove rt6_qualify_for_ecmp which is just guess work. It fails in 2 cases:
1. can not replace a route with a reject route. Existing code appends
   a new route instead of replacing the existing one.

2. can not have a multipath route where a leg uses a dev only nexthop

Existing use cases affected by this change:
1. adding a route with existing prefix and metric using NLM_F_CREATE
   without NLM_F_APPEND or NLM_F_EXCL (ie., what iproute2 calls
   'prepend'). Existing code auto-determines that the new nexthop can
   be appended to an existing route to create a multipath route. This
   change breaks that by requiring the APPEND flag for the new route
   to be added to an existing one. Instead the prepend just adds another
   route entry.

2. route replace. Existing code replaces first matching multipath route
   if new route is multipath capable and fallback to first matching
   non-ECMP route (reject or dev only route) in case one isn't available.
   New behavior replaces first matching route. (Thanks to Ido for spotting
   this one)

Note: Newer iproute2 is needed to display multipath routes with a dev-only
      nexthop. This is due to a bug in iproute2 and parsing nexthops.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Ahern 2018-05-21 10:26:53 -07:00 • committed by David S. Miller
parent 5a15a1b07c
commit f34436a430
3 changed files with 73 additions and 93 deletions
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3
net/ipv6/route.c
View file

@ -3791,7 +3791,7 @@ static struct fib6_info *rt6_multipath_first_sibling(const struct fib6_info *rt)
lockdep_is_held(&rt->fib6_table->tb6_lock));
while (iter) {
if (iter->fib6_metric == rt->fib6_metric &&
rt6_qualify_for_ecmp(iter))
iter->fib6_nsiblings)
return iter;
iter = rcu_dereference_protected(iter->fib6_next,
lockdep_is_held(&rt->fib6_table->tb6_lock));
@ -4381,6 +4381,7 @@ static int ip6_route_multipath_add(struct fib6_config *cfg,
*/
cfg->fc_nlinfo.nlh->nlmsg_flags &= ~(NLM_F_EXCL |
NLM_F_REPLACE);
cfg->fc_nlinfo.nlh->nlmsg_flags |= NLM_F_APPEND;
nhn++;
}