netdev - Re: [PATCH net-next v3 1/2] netlink: ipv4 igmp join notifications

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Date:   Tue, 25 Sep 2018 10:34:03 +0100
From:   Patrick Ruddy <pruddy@...tta.att-mail.com>
To:     David Ahern <dsahern@...il.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Jiří Pírko <jiri@...nulli.us>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Subject: Re: [PATCH net-next v3 1/2] netlink: ipv4 igmp join notifications

On Wed, 2018-09-19 at 21:47 -0700, David Ahern wrote:
> On 9/18/18 6:12 AM, Patrick Ruddy wrote:
> > 
> > I've hit a small snag with adding the new groups. The number of defined
> > groups currently sits at 31 so I can only add one before hitting the
> 
> I believe you have no more available. RTNLGRP_* has been defined from 0
> (RTNLGRP_NONE) to 31 (RTNLGRP_IPV6_MROUTE_R) which covers the u32 range.
> 
> > limit defined by the 32 bit groups bitmask in socakddr_nl. I can use 1
> > group for both v4 and v6 notifications which seems like the sensible
> > options since the AF is carried separately, but it breaks the precedent
> > where there are separate IPV4 and IPV6 groups for IFADDR.
> > 
> > I have the combined group patches ready and can share them if that's
> > the preference.
> > 
> > Has there been any previous discussion about extending the number of
> > availabel groups?
> > 
> 
> I have not tried it, but from a prior code review I believe you have you
> use setsockopt to add groups > 31.

I can certainly join the new groups using setsockopt and
NETLINK_ADD_MEMBERSHIP.
I can't see any examples of extending the defined group list within the
kernel so I assume I just add to the RTNLGRP enum list with a suitable
comment to indicate that later groups must be joined with the mechanism
above or am I missing some other way of dynamically adding groups?

thanks

-pr