netdev - Re: [PATCH net-next v3 0/4] net: ipv6: Improve user experience with multipath routes

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Message-ID: <5be4a78e-64b8-abc4-4015-6751a2bab12b@cumulusnetworks.com>
Date:   Sun, 29 Jan 2017 19:57:55 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     netdev@...r.kernel.org, nicolas.dichtel@...nd.com
Subject: Re: [PATCH net-next v3 0/4] net: ipv6: Improve user experience with
 multipath routes

On 1/29/17 7:20 PM, Roopa Prabhu wrote:
>> 2. Delete - 1 notification for each hop for all combinations of delete commands
> 
> here I was trying to say, for people deleting the full multipath route, you should send a RTA_MULTIPATH.

The only way to do that is to call inet6_rt_notify() *before* the route delete work has been done in fib6_del_route. Right now it is called at the end - after all sibling associations have been dropped, a time in which it can no longer fill in RTA_MULTIPATH.

fib6_del_route function does not have any failure paths and is called with the write lock held, so moving the notification might be ok. But it also means ignoring all subsequent failures from fib6_del, again which might be ok since the only failure is ENOENT which can not happen if we are walking the sibling list.

> For the odd case of ipv6 single nexthop delete, you can continue to send a single nexthop delete (like today ..without RTA_MULTIPATH)
> because there is no other way to notify a single nexthop delete with a RTM_DELROUTE.
> 
> The reason I say this is because: keeping future in mind, this will make things consistent for majority of people who will
> start using RTA_MULTIPATH for both ipv4 and ipv6 for adds and deletes (requests/notifications and dumps) the same way.
> single next hop delete will just be around because of fear of breaking existing applications.

Single next hop delete will be around because IPv6 allows it -- and because IPv4 needs to support it.