netdev - Re: [PATCH net-next v3 2/3] net: ipv4: add sysctl for nexthop api compatibility mode

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Message-ID: <CAJieiUg+oC1Q-EUgYsmGRnmzPb_tnacQ8_6oFC0EavSmOqHEZQ@mail.gmail.com>
Date:   Mon, 27 Apr 2020 10:00:20 -0700
From:   Roopa Prabhu <roopa@...ulusnetworks.com>
To:     David Ahern <dsahern@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Benjamin Poirier <bpoirier@...ulusnetworks.com>
Subject: Re: [PATCH net-next v3 2/3] net: ipv4: add sysctl for nexthop api
 compatibility mode

On Mon, Apr 27, 2020 at 6:12 AM David Ahern <dsahern@...il.com> wrote:
>
> On 4/26/20 9:41 PM, Roopa Prabhu wrote:
> > diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> > index 6fcfd31..02029b5 100644
> > --- a/Documentation/networking/ip-sysctl.txt
> > +++ b/Documentation/networking/ip-sysctl.txt
> > @@ -1553,6 +1553,20 @@ skip_notify_on_dev_down - BOOLEAN
> >       on userspace caches to track link events and evict routes.
> >       Default: false (generate message)
> >
> > +nexthop_compat_mode - BOOLEAN
> > +     Controls whether new route nexthop API is backward compatible
> > +     with old route API. By default Route nexthop API maintains
> > +     user space compatibility with old route API: Which means
> > +     Route dumps and netlink notifications include both new and
> > +     old route attributes. In systems which have moved to the new API,
> > +     this compatibility mode provides a way to turn off the old
> > +     notifications and route attributes in dumps. This sysctl is on
> > +     by default but provides the ability to turn off compatibility
> > +     mode allowing systems to run entirely with the new routing
> > +     nexthop API. Old route API behaviour and support is not modified
> > +     by this sysctl
> > +     Default: true (backward compat mode)
> > +
>
> That description is a bit confusing, to me at least. It would be better
> to state what changes happen when the sysctl is disabled. Something like:
>
> New nexthop API provides a means for managing nexthops independent of
> prefixes. Backwards compatibilty with old route format is enabled by
> default which means route dumps and notifications contain the new
> nexthop attribute but also the full, expanded nexthop definition.
> Further, updates or deletes of a nexthop configuration generate route
> notifications for each fib entry using the nexthop. Once a system
> understands the new API, this sysctl can be disabled to achieve full
> performance benefits of the new API by disabling the nexthop expansion
> and extraneous notifications.

sure, I will take what you have. will send v4