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

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Date:   Fri, 14 Apr 2017 22:26:18 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     vyasevic@...hat.com, Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: Re: [PATCH net-next 1/8] rtnetlink: Do not generate notifications for
 MTU events

+Nicolas

On 4/14/17 7:51 PM, Vlad Yasevich wrote:
> On 04/10/2017 11:49 AM, David Ahern wrote:
>> On 4/10/17 9:39 AM, Vlad Yasevich wrote:
>>> OK, so this will work for the events that are generated as a result of device state change
>>> (like mtu, address, and others).
>>>
>>> However, the original event data may be needed for other events that may be
>>> of use to userspace like NETDEV_NOTIFY_PEERS and NETDEV_RESEND_IGMP (possibly others...)
>>
>> sure. My objection is to multiple messages with identical content.
>>
>> I think the rtnetlink_event message is unique for those 2 netdev events,
>> so no objections if it has value.
>>
> 
> So, I've been looking at adding a bitmap and collecting all modification, however
> I ran into an interesting issue in do_setlink.
> 
> Currently the notifications from do_setlink() don't appear to work as one would
> expect and it's somewhat confusing upon deeper inspection.
> 
> We have 2 values DO_SETLINK_MODIFIED (1) and DO_SETLINK_NOTIFY (3).  These 2 'attempt'
> to do different jobs, but really fail at it.  The function will generate notifications
> regardless of which of the above values is used.
> 
> Those changes were done in commit ba9989069f4e426b1e0ed7018eacc9e1ba607095 (cc Nicolas
> just in case he remembers the history)
> 
> I am not sure which changes should really trigger a call netdev_state_change(), thus this
> message.  Right now, all changes done in this function trigger them.  If that's how that
> should function, that I can simplify the code.  If not, then some of the changes may
> require us to export the event to the user.
> 
> To use the dreaded NETDEV_CHANGEMTU event as an example, we used to generate 3 messages
> (PRECHANGEMTU, CHANGEMTU, and a message from netdev_state_change).  With recent changes,
> we now only generate a message from netdev_state_change.  However, mtu change is tagged
> with DO_SETLINK_MODIFIED which doesn't include the notify bit.  So, should there be a
> NETDEV_CHANGE event associated with this change and a rtnl message (as it is now) or not?
> It's unclear.
> 
> -vlad
>