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

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Date:   Thu, 13 Sep 2018 18:49:13 +0100
From:   Patrick Ruddy <pruddy@...tta.att-mail.com>
To:     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 Thu, 2018-09-13 at 10:03 -0700, Roopa Prabhu wrote:
> On Thu, Sep 6, 2018 at 8:40 PM, Roopa Prabhu <roopa@...ulusnetworks.com> wrote:
> > On Thu, Sep 6, 2018 at 2:10 AM, Patrick Ruddy
> > <pruddy@...tta.att-mail.com> wrote:
> > > Some userspace applications need to know about IGMP joins from the
> > > kernel for 2 reasons:
> > > 1. To allow the programming of multicast MAC filters in hardware
> > > 2. To form a multicast FORUS list for non link-local multicast
> > >    groups to be sent to the kernel and from there to the interested
> > >    party.
> > > (1) can be fulfilled but simply sending the hardware multicast MAC
> > > address to be programmed but (2) requires the L3 address to be sent
> > > since this cannot be constructed from the MAC address whereas the
> > > reverse translation is a standard library function.
> > > 
> > > This commit provides addition and deletion of multicast addresses
> > > using the RTM_NEWMDB and RTM_DELMDB messages with AF_INET. It also
> > > provides the RTM_GETMDB extension to allow multicast join state to
> > > be read from the kernel.
> > > 
> > > Signed-off-by: Patrick Ruddy <pruddy@...tta.att-mail.com>
> > > ---
> > > v3 rework to use RTM_***MDB messages as per review comments.
> > 
> > Patrick, this version seems to be using RTM_***MDB msgs with the
> > RTM_*ADDR format.
> > We cant do that...because existing RTM_MDB users will be confused.
> > 
> > My request was to evaluate RTM_***MDB msg format. see
> > nlmsg_populate_mdb_fill for details.
> > 
> > If you can wait a day or two I can share some experimental code that
> > moves high level RTM_*MDB msg handling into net/core/rtnetlink.c
> > similar to RTM_*FDB
> > 
> 
> I was trying to get a default per interface (non bridge) RTM_*MDB
> working, but realized that the dev->mc
> entries are already getting dumped as part of RTM_*FDB msgs instead of
> RTM_*MDB. (see net/core/rtnetlink.c:ndo_dflt_fdb_dump).
> This adds another wrench.
> 
> so, that puts us back to your use of RTM_NEWADDR.
> Instead of using IFA_ADDRESS, you could introduce a new one
> IFA_IGMP_MULTICAST  (since IFA_MULTICAST is already taken).
> 
> 
> To keep existing users of RTM_NEWADDR unaffected. I think you can use
> the IPMR family with RTM_NEWADDR.
> We can introduce new notification group. (We can choose to add a new
> family too, but that seems unnecessary)
> 
> since you only need dumps:
> rtnl_register(RTNL_FAMILY_IPMR, RTM_GETADDR, NULL, igmp_rtm_dumpaddrs, 0);
> 
> For notifications, since we already have many variants for routes, I
> don't see a problem adding similar addr variants
> RTNLGRP_IPV4_MCADDR
> 
> (Others on the list may have more feedback).
Thanks for looking at this Roopa - I'll rehash as suggested.

-pr