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[Xen-devel] [PATCH] public/io/netif.h: document a mechanism to advertise carrier state

This patch adds a specification for a 'carrier' node in xenstore to allow
a backend to notify a frontend of it's virtual carrier/link state. E.g.
a backend that is unable to forward packets from the guest because it is
not attached to a bridge may wish to advertise 'no carrier'.

NOTE: This is purely a documentation patch. No functional change.

Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
 xen/include/public/io/netif.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
index 2454448baa..e587055f68 100644
--- a/xen/include/public/io/netif.h
+++ b/xen/include/public/io/netif.h
@@ -190,6 +190,20 @@
  * order as requests.
+ * Link state
+ * ==========
+ *
+ * The backend can advertise it is current link (carrier) state to the
+ * frontend using the /local/domain/X/backend/<domid>/<vif>/carrier node.
+ * If this node is not present, then the frontend should assume that the
+ * link is up (for compatibility with backends that do no implement this
+ * feature). If this node is present, then a value of "0" should be
+ * interpreted by the frontend as the link being down (no carrier) and a
+ * value of "1" should be interpreted as the link being up (carrier
+ * present).
+ */
  * Hash types
  * ==========

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