netdev - Re: [PATCH net-next v2 1/2] netlink: ipv4 igmp join notifications

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Date:   Tue, 04 Sep 2018 08:54:07 +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>
Subject: Re: [PATCH net-next v2 1/2] netlink: ipv4 igmp join notifications

On Mon, 2018-09-03 at 16:12 -0700, Roopa Prabhu wrote:
> On Sun, Sep 2, 2018 at 4:18 AM, Patrick Ruddy
> <pruddy@...tta.att-mail.com> wrote:
> > Hi Roopa
> > 
> > inline
> > 
> > thx
> > 
> > -pr
> > 
> > On Fri, 2018-08-31 at 09:29 -0700, Roopa Prabhu wrote:
> > > On Fri, Aug 31, 2018 at 4:20 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_NEWADDR and RTM_DELADDR messages. It also provides
> > > > the RTM_GETADDR extension to allow multicast join state to be read
> > > > from the kernel.
> > > > 
> > > > Signed-off-by: Patrick Ruddy <pruddy@...tta.att-mail.com>
> > > > ---
> > > > v2: fix kbuild warnings.
> > > 
> > > I am still going through the series, but AFAICT, user-space caches listening to
> > > RTNLGRP_IPV4_IFADDR will now also get multicast addresses by default ?
> > > 
> > 
> > Yes that's the crux of this change. It's unfortunate that I could not
> > use IFA_MULTICAST to distinguish the SAFI. I suppose the other option
> > would be to create a set of new NEW/DEL/GETMULTICAST messages but the
> > partial code for RTM_GETMULTICAST in ipv6/mcast.c complicates that
> > slightly. Happy to look at it if you think that would be be better.
> > 
> 
> yeah, true. Thinking about this some more, you are adding an interface
> for multicast entries learnt via igmp.
> There is already a netlink channel for layer2 mc addresses via igmp. I
> can't see why that cannot be used.
> It is RTM_*MDB msgs. It is currently only available for the bridge.
> But, I have a requirement for it to be
> available via a vxlan dev...so, I am looking at making it available on
> other devices.
>  
> The reason I think it should be possible is because this is similar to
> bridge fdb entries.
> The bridge fdb api  (RTM_NEWNEIGH with AF_BRIDGE) is overloaded to
> notify and dump netdev unicast addresses.
> similarly I think the mdb api can be overloaded to notify and dump
> netdev multicast addresses (statically added or learnt via igmp)
OK I'll take a look at this.