From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Durrant Subject: Re: [PATCH] public/io/netif.h: change semantics of "request-multicast-control" flag Date: Wed, 20 Jan 2016 13:14:08 +0000 Message-ID: References: <1453294249-6346-1-git-send-email-paul.durrant@citrix.com> <1453295177.26343.115.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1aLsaR-0000w8-8X for xen-devel@lists.xenproject.org; Wed, 20 Jan 2016 13:14:11 +0000 In-Reply-To: <1453295177.26343.115.camel@citrix.com> Content-Language: en-US List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell , "xen-devel@lists.xenproject.org" Cc: Ian Jackson , "Keir (Xen.org)" , Jan Beulich , "Tim (Xen.org)" List-Id: xen-devel@lists.xenproject.org > -----Original Message----- > From: Ian Campbell [mailto:ian.campbell@citrix.com] > Sent: 20 January 2016 13:06 > To: Paul Durrant; xen-devel@lists.xenproject.org > Cc: Ian Jackson; Jan Beulich; Keir (Xen.org); Tim (Xen.org) > Subject: Re: [PATCH] public/io/netif.h: change semantics of "request- > multicast-control" flag > > On Wed, 2016-01-20 at 12:50 +0000, Paul Durrant wrote: > > My patch b2700877 "move and amend multicast control documentation" > > clarified use of the multicast control protocol between frontend and > > backend. However, it transpires that the restrictions that documentation > > placed on the "request-multicast-control" flag make it hard for a > > frontend to enable 'all multicast' promiscuous mode, in that to do so > > would require the frontend and backend to disconnect and re-connect. > > Do we therefore think that this document reflected reality, i.e. might this > not be "just" a documentation bug? > > (Or maybe we can't tell because the only previous implementation was years > ago in Solaris or something) That's my concern. I hope it's just a documentation bug, but I don't know. Also I've already done an implementation in Linux netback according to the restricted semantics. > > > This patch adds a new "feature-dynamic-multicast-control" flag to allow > > a backend to advertise that it will watch "request-multicast-control" hence > > allowing it to be meaningfully modified by the frontend at any time rather > > than only when the frontend and backend are disconnected. > > Would allowing XEN_NETIF_EXTRA_TYPE_MCAST_{ADD,DEL} to take a bcast > address > be easier on the backend, in that it would just need to be a static feature > rather than watching stuff on the fly? The documented semantics of the list are 'exact match' so sending a bcast address doesn't do much good with a backend that doesn't know to treat is specially hence a frontend can't tell whether 'all multicast' mode is going to work without the extra feature flag. As for watching "request-multcast-control" vs. add/remove of bcast, the complexity of implementation is cheaper for the latter but I think the former is 'nicer'. Paul