netdev - Re: [PATCH v2 net-next] net/ipv6: Add knob to skip DELROUTE message on device down

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Date:   Fri, 12 Oct 2018 09:49:23 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     dsahern@...nel.org
Cc:     netdev@...r.kernel.org, roopa@...ulusnetworks.com,
        dsahern@...il.com
Subject: Re: [PATCH v2 net-next] net/ipv6: Add knob to skip DELROUTE
 message on device down

From: David Ahern <dsahern@...nel.org>
Date: Thu, 11 Oct 2018 20:17:21 -0700

> From: David Ahern <dsahern@...il.com>
> 
> Another difference between IPv4 and IPv6 is the generation of RTM_DELROUTE
> notifications when a device is taken down (admin down) or deleted. IPv4
> does not generate a message for routes evicted by the down or delete;
> IPv6 does. A NOS at scale really needs to avoid these messages and have
> IPv4 and IPv6 behave similarly, relying on userspace to handle link
> notifications and evict the routes.
> 
> At this point existing user behavior needs to be preserved. Since
> notifications are a global action (not per app) the only way to preserve
> existing behavior and allow the messages to be skipped is to add a new
> sysctl (net/ipv6/route/skip_notify_on_dev_down) which can be set to
> disable the notificatioons.
> 
> IPv6 route code already supports the option to skip the message (it is
> used for multipath routes for example). Besides the new sysctl we need
> to pass the skip_notify setting through the generic fib6_clean and
> fib6_walk functions to fib6_clean_node and to set skip_notify on calls
> to __ip_del_rt for the addrconf_ifdown path.
> 
> Signed-off-by: David Ahern <dsahern@...il.com>
> ---
> v2
> - removed the changes to addrconf and anycast. addrconf_ifdown calls
>   rt6_disable_ip which calls rt6_sync_down_dev. The last one evicts all
>   routes for the device, so the delete route calls done later in addrconf
>   and anycast are superfluous

Applied.