[Xen-devel] [PATCH] public/io/netif.h: document xenstore negotiation of multicast control

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

netif.h contains a specification of the XEN_NETIF_EXTRA_TYPE_MCAST_{ADD,DEL}
extra info messages require to manipulate a multicast filter list maintained
by a backend but does not specify how the multicast contol feature should
be negotiated in xenstore. This patch attempts to rectify that.

To determine the correct sequence I mined the xen-devel archives to
ascertain the intention of the original submitter of the patch (see thread
starting at
http://lists.xenproject.org/archives/html/xen-devel/2007-11/msg00687.html)
and also examined how the feature is implemented by the illumos xnb/xnf
drivers, which I believe form the only concrete example.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
---
 xen/include/public/io/netif.h |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
index 353eab7..6599c5a 100644
--- a/xen/include/public/io/netif.h
+++ b/xen/include/public/io/netif.h
@@ -136,6 +136,19 @@
  */
 
 /*
+ * "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
+ * drop any multicast packet that does not match in a filter list. The list is
+ * amended by the frontend by sending XEN_NETIF_EXTRA_TYPE_MCAST_{ADD,DEL}
+ * messages as specified below.
+ * Once enabled by the frontend, the feature cannot be disabled except by
+ * closing and re-connecting to the backend.
+ */
+
+/*
  * This is the 'wire' format for packets:
  *  Request 1: netif_tx_request_t -- NETTXF_* (any flags)
  * [Request 2: netif_extra_info_t] (only if request 1 has NETTXF_extra_info)
-- 
1.7.10.4


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