[PATCH RFC 1/8] public/io/blkif: add directory for backend parameters

[Joao Martins <joao.m.martins@oracle.com>]

The proposed directory provides a mechanism for tools to control the
maximum feature set of the device being provisioned by backends.
Examples include max ring page order, persistent grants, number of
queues etc.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 xen/include/public/io/blkif.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/xen/include/public/io/blkif.h b/xen/include/public/io/blkif.h
index 15a71e3fea..4c0a93a2bf 100644
--- a/xen/include/public/io/blkif.h
+++ b/xen/include/public/io/blkif.h
@@ -133,6 +133,20 @@
  *      This option doesn't require a backend to use O_DIRECT, so it
  *      should not be used to try to control the caching behaviour.
  *
+ * require
+ *
+ *      The directory "require" maybe be created by tools domain to
+ *      override the maximum feature set that backend provides to the
+ *      frontend. The children entries within this directory are
+ *      features names and its correspondent value e.g.:
+ *
+ *      /local/domain/X/backend/vbd/<domid>/<devno>/require
+ *      /local/domain/X/backend/vbd/<domid>/<devno>/require/multi-queue-max-queues = "2"
+ *      /local/domain/X/backend/vbd/<domid>/<devno>/require/feature-persistent = "0"
+ *
+ *      In the example above, block backend will negotiate up to a maximum of
+ *      two queues with frontend plus disabling persistent grants.
+ *
  *--------------------------------- Features ---------------------------------
  *
  * feature-barrier
-- 
2.11.0


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