netdev - Re: [PATCH net-next 1/8] rtnetlink: Do not generate notifications for MTU events

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Date:   Sat, 08 Apr 2017 11:06:17 -0700
From:   Roopa Prabhu <roopa@...ulusnetworks.com>
To:     David Ahern <dsa@...ulusnetworks.com>
CC:     netdev@...r.kernel.org, vyasevic@...hat.com, davem@...emloft.net
Subject: Re: [PATCH net-next 1/8] rtnetlink: Do not generate notifications
 for MTU events

On 4/7/17, 2:25 PM, David Ahern wrote:
> Changing MTU on a link currently causes 3 messages to be sent to userspace:
>
> [LINK]11: dummy1: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1490 qdisc noqueue state UNKNOWN group default event PRE_CHANGE_MTU
>     link/ether f2:52:5c:6d:21:f3 brd ff:ff:ff:ff:ff:ff
>
> [LINK]11: dummy1: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default event CHANGE_MTU
>     link/ether f2:52:5c:6d:21:f3 brd ff:ff:ff:ff:ff:ff
>
> [LINK]11: dummy1: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default
>     link/ether f2:52:5c:6d:21:f3 brd ff:ff:ff:ff:ff:ff
>
> Remove the PRE_CHANGE_MTU and CHANGE_MTU messages.
>
>

This change is good... multiple notifications for the same event does not help in large scale links setups. However, this
reverts what vlad was trying to do with his patchset. Vlad's patch-set relies on the rtnl notifications generated from
notifiers (rtnetlink_event) to add  specific event (IFLA_EVENT) in notifications.

The third notification in your example above is the correct one and is an aggregate notification for a set of changes, but
it cannot really fill in all types of events in the single IFLA_EVENT attribute as it stands today.  IFLA_EVENT should be
a bitmask to include all events in this case (i had indicated this in vlads first version).