[PATCH] blkif.h: document scsi/0x12/0x<NN> node

[Bob Liu <bob.liu@oracle.com>]

This patch documents a xenstore node which is used by XENVBD Windows PV
driver.

The use case is that XenServer may have OEM specific storage backends and
there is requirement to run OEM software in guest which relied on VPD
information supplied by the storages.
Adding a node to xenstore is the easiest way to get this VPD information from
the backend into guest where XENVBD Windows PV driver can get INQUIRY VPD data
from this node and return to OEM software.

Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
 xen/include/public/io/blkif.h |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/xen/include/public/io/blkif.h b/xen/include/public/io/blkif.h
index 99f0326..afbcbff 100644
--- a/xen/include/public/io/blkif.h
+++ b/xen/include/public/io/blkif.h
@@ -182,6 +182,30 @@
  *      backend driver paired with a LIFO queue in the frontend will
  *      allow us to have better performance in this scenario.
  *
+ * scsi/0x12/0x<NN>
+ *	Values: base64 encoded string
+ *
+ *	This optional node contains SCSI INQUIRY VPD information.
+ *	<NN> is the hexadecimal representation of the VPD page code.
+ *	Currently only XENVBD Windows PV driver is using this node.
+ *
+ *	A frontend e.g XENVBD Windows PV driver which represents a Xen VBD to
+ *	its containing operating system as a (virtual) SCSI target may return the
+ *	specified data in response to INQUIRY commands from its containing OS.
+ *
+ *	A frontend which supports this feature must return the backend-specified
+ *	data for every INQUIRY command with the EVPD bit set.
+ *	For EVPD=1 INQUIRY commands where the corresponding xenstore node
+ *	does not exist, the frontend must report (to its containing OS) an
+ *	appropriate failure condition.
+ *
+ *	A frontend which does not support this feature just disregard these
+ *	xenstore nodes.
+ *
+ *	The data of this string node is base64 encoded. Base64 is a group of
+ *	similar binary-to-text encoding schemes that represent binary data in an
+ *	ASCII string format by translating it into a radix-64 representation.
+ *
  *----------------------- Request Transport Parameters ------------------------
  *
  * max-ring-page-order
-- 
1.7.10.4


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