netdev - Re: [PATCH net-next] rtnl: Add support for netdev event to link messages

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Date:   Thu, 30 Mar 2017 08:11:23 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     vyasevic@...hat.com, Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] rtnl: Add support for netdev event to link
 messages

On 3/30/17 7:47 AM, Vlad Yasevich wrote:
>>>>> But, NETDEV_PRECHANGEMTU will be a unnecessary notification to userspace without
>>>>> changes. There are already enough notifications generated for links (I know you are not
>>>>> suggesting adding it here)
>>>>
>>>> Actually, this one already triggers a link notification to userspace.  It just has
>>>> no event data in it to tell you that. :)
>>>
>>> Is it intentional or unintentional? perhaps rtnetlink_event should be a
>>> whitelist -- events that userspace should be notified about. Seems like
>>> NETDEV_ events have been added without rtnetlink_event getting updated.
>>
>> I think a 'whitelist' was attempted, but as you mentioned, it hasn't been updated...
>> I'll defer the definitive answer to someone else.  It seems Patrick added a comment
>> in commit a2835763 to update the white list and it's been a few times.
>>
> 
> This is actually an interesting point.  Looking at some commits that have added
> events to black list in rtnetlink-event, it might have been much easier to debug
> those issues if we had the 'event' encoding in the netlink message.
> 
> I think it might be worthwhile to add all allowed event types to this new encoding
> so we can userspace can see just what's its getting.
> 

My point is that it is easy to add NETDEV events; takes extra effort to
update rtnetlink_event to say "don't send a notification to userspace".

A number of those events are for kernel processing, so why send anything
to userspace? In that case a default of don't notify userspace and then
having a list of events that should send the notification makes the
intent explicit.

Looking at git commit logs for NETDEV_PRECHANGEMTU, it seems that it was
added for bonding and teaming to simplify kernel processing; userspace
does not need to be notified so no intention there.