netdev - Re: [PATCH net-next V3 2/2] rtnl: Add support for netdev event attribute to link messages

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Date:   Mon, 24 Apr 2017 08:14:38 -0700
From:   Roopa Prabhu <roopa@...ulusnetworks.com>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     Vladislav Yasevich <vyasevich@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Vladislav Yasevich <vyasevic@...hat.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH net-next V3 2/2] rtnl: Add support for netdev event
 attribute to link messages

On Sun, Apr 23, 2017 at 6:07 PM, David Ahern <dsa@...ulusnetworks.com> wrote:
>
> On 4/21/17 11:31 AM, Vladislav Yasevich wrote:
> > @@ -1276,9 +1277,40 @@ static int rtnl_xdp_fill(struct sk_buff *skb, struct net_device *dev)
> >       return err;
> >  }
> >
> > +static int rtnl_fill_link_event(struct sk_buff *skb, unsigned long event)
> > +{
> > +     u32 rtnl_event;
> > +
> > +     switch (event) {
> > +     case NETDEV_REBOOT:
> > +             rtnl_event = IFLA_EVENT_REBOOT;
> > +             break;
> > +     case NETDEV_FEAT_CHANGE:
> > +             rtnl_event = IFLA_EVENT_FEAT_CHANGE;
> > +             break;
> > +     case NETDEV_BONDING_FAILOVER:
> > +             rtnl_event = IFLA_EVENT_BONDING_FAILOVER;
> > +             break;
> > +     case NETDEV_NOTIFY_PEERS:
> > +             rtnl_event = IFLA_EVENT_NOTIFY_PEERS;
> > +             break;
> > +     case NETDEV_RESEND_IGMP:
> > +             rtnl_event = IFLA_EVENT_RESEND_IGMP;
> > +             break;
> > +     case NETDEV_CHANGEINFODATA:
> > +             rtnl_event = IFLA_EVENT_CHANGE_INFO_DATA;
> > +             break;
> > +     default:
> > +             return 0;
> > +     }
> > +
> > +     return nla_put_u32(skb, IFLA_EVENT, rtnl_event);
> > +}
> > +
>
> I still have doubts about encoding kernel events into a uapi.

agree. I don't see why user-space will need NETDEV_CHANGEINFODATA and
others david listed.

My other concerns are, once we have this exposed to user-space and
user-space starts relying on it, it will need accurate information and
will expect to have this event information all the time.
IIUC, we cannot cover multiple events in a single notification and not
all link notifications will contain an IFLA_EVENT attribute. In other
words, we will be telling user-space to not expect that the kernel
will send IFLA_EVENT every time.



>
> For example, NETDEV_CHANGEINFODATA is only for bonds though nothing
> about the name suggests it is a bonding notification. This one was added
> specifically to notify userspace (d4261e5650004), yet seems to happen
> only during a changelink and that already generates a RTM_NEWLINK
> message via do_setlink. Since the rtnetlink_event message does not
> contain anything "NETDEV_CHANGEINFODATA" related what purpose does it
> really serve besides duplicating netlink messages to userspace.
>
> The REBOOT, IGMP, FEAT_CHANGE and BONDING_FAILOVER seem to be unique
> messages (code analysis only) which I get for notifying userspace.
>
> NETDEV_NOTIFY_PEERS is not so clear in how often it duplicates other
> messages.