Re: [PATCH] public/io/netif.h: change semantics of "request-multicast-control" flag

[Ian Campbell <ian.campbell@citrix.com>]

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.
> 
> 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.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Cc: Ian Campbell <ian.campbell@citrix.com>
> Cc: Ian Jackson <ian.jackson@eu.citrix.com>
> Cc: Jan Beulich <jbeulich@suse.com>
> Cc: Keir Fraser <keir@xen.org>
> Cc: Tim Deegan <tim@xen.org>


This looks good to me, but also adding Wei (Linux netback + BSD stuff) and
Roger (BSD stuff) for their perspective.

I should probably have done that for the last set of netif.h changes too,
since apart from the nominal maintainers of xen/include/public/io/*.h it's
worth getting input from the maintainers of the consumers. Not sure we can
express that very well in MAINTAINERS :-(.

Ian.

> ---
>  xen/include/public/io/netif.h | 34 ++++++++++++++++++++++------------
>  1 file changed, 22 insertions(+), 12 deletions(-)
> 
> diff --git a/xen/include/public/io/netif.h
> b/xen/include/public/io/netif.h
> index fe0a87f..8816e0f 100644
> --- a/xen/include/public/io/netif.h
> +++ b/xen/include/public/io/netif.h
> @@ -136,18 +136,28 @@
>   */
>  
>  /*
> - * "feature-multicast-control" advertises the capability to filter ethernet
> - * multicast packets in the backend. To enable use of this capability the
> - * frontend must set "request-multicast-control" before moving into the
> - * connected state.
> - *
> - * If "request-multicast-control" is set then the backend transmit side should
> - * no longer flood multicast packets to the frontend, it should instead drop any
> - * multicast packet that does not match in a filter list. The list is
> - * amended by the frontend by sending dummy transmit requests containing
> - * XEN_NETIF_EXTRA_TYPE_MCAST_{ADD,DEL} extra-info fragments as specified below.
> - * Once enabled by the frontend, the feature cannot be disabled except by
> - * closing and re-connecting to the backend.
> + * "feature-multicast-control" and "feature-dynamic-multicast-control"
> + * advertise the capability to filter ethernet multicast packets in the
> + * backend. If the frontend wishes to take advantage of this feature then
> + * it may set "request-multicast-control". If the backend only advertises
> + * "feature-multicast-control" then "request-multicast-control" must be set
> + * before the frontend moves into the connected state. The backend will
> + * sample the value on this state transition and any subsequent change in
> + * value will have no effect. However, if the backend also advertises
> + * "feature-dynamic-multicast-control" then "request-multicast-control"
> + * may be set by the frontend at any time. In this case, the backend will
> + * watch the value and re-sample on watch events.
> + *
> + * If the sampled value of "request-multicast-control" is set then the
> + * backend transmit side should no longer flood multicast packets to the
> + * frontend, it should instead drop any multicast packet that does not
> + * match in a filter list.
> + * The list is amended by the frontend by sending dummy transmit requests
> + * containing XEN_NETIF_EXTRA_TYPE_MCAST_{ADD,DEL} extra-info fragments as
> + * specified below.
> + * Note that the filter list may be amended even if the sampled value of
> + * "request-multicast-control" is not set, however the filter should only
> + * be applied if it is set.
>   */
>  
>  /*

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