netdev - Re: [PATCH net-next v2 0/2] net: ipv6: Improve user experience with multipath routes

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Date:   Fri, 20 Jan 2017 12:31:44 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 0/2] net: ipv6: Improve user experience with
 multipath routes

On 1/19/17 11:10 PM, David Ahern wrote:
> This series closes a couple of gaps between IPv4 and IPv6 with respect
> to multipath routes:
...
> In both cases, the new behavior requires users to opt in by setting a new
> flag, RTM_F_ALL_NEXTHOPS, in the rtm_flags of struct rtmsg which is
> expected to be the ancillary header in the netlink request received from
> the user. A program must opt in to the new behavior so as to not break
> any existing applications.
> 
> The opt-in behavior works for both route deletes and dumps (the two
> differences noted above), but not for notifications as notifications
> do not take user input to specify flags. The only way to have
> notifications generate RTA_MULTIPATH encodings is to have a gobal
> flag -- e.g., sysctl. I'd prefer not to add a sysctl knob for this
> backwards compatibility.

BTW, I am in favor of not requiring a user API for this but just doing it. I can't imagine anyone working with multipath routes not wanting the efficiency of the RTA_MULTIPATH attribute. These patches require an API only because of the rule not to break userspace. If we conclude to just do it without an API, the multipath_add and multipath_del need to be modified to only send a notification once at the end of the actions.