[Xen-devel] [PATCH v3] public/io/netif.h: document a mechanism to advertise carrier state

[Paul Durrant <pdurrant@xxxxxxxxxx>]

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'.

While in the area also fix an erroneous backend path description.

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

Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
---
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

v3:
 - Fix another typo

v2:
 - Fix text
 - Fix path
---
 xen/include/public/io/netif.h | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
index 2454448baa..9fcf91a2fe 100644
--- a/xen/include/public/io/netif.h
+++ b/xen/include/public/io/netif.h
@@ -171,7 +171,7 @@
  * The ability of the backend to use a control ring is advertised by
  * setting:
  *
- * /local/domain/X/backend/<domid>/<vif>/feature-ctrl-ring = "1"
+ * /local/domain/X/backend/vif/<domid>/<vif>/feature-ctrl-ring = "1"
  *
  * The frontend provides a control ring to the backend by setting:
  *
@@ -190,6 +190,20 @@
  * order as requests.
  */
 
+/*
+ * Link state
+ * ==========
+ *
+ * The backend can advertise its current link (carrier) state to the
+ * frontend using the /local/domain/X/backend/vif/<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 not 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
  * ==========
-- 
2.20.1


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