On 3/30/17 7:47 AM, Vlad Yasevich wrote:

quoted

quoted

quoted

quoted

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.