[PATCH] Drivers: hv: vss: run only on supported host versions

[Olaf Hering <olaf@aepfle.de>]

The Backup integration service on WS2012 has appearently trouble to
negotiate with a guest which does not support the provided util version.
Currently the VSS driver supports only version 5/0. A WS2012 offers only
version 1/x and 3/x, and vmbus_prep_negotiate_resp correctly returns an
empty icframe_vercnt/icmsg_vercnt. But the host ignores that and
continues to send ICMSGTYPE_NEGOTIATE messages. The result are weird
errors during boot and general misbehaviour.

Check the Windows version to work around the host bug, skip hv_vss_init
on WS2012 and older.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 drivers/hv/hv_snapshot.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
index a548ae4..52f10ed 100644
--- a/drivers/hv/hv_snapshot.c
+++ b/drivers/hv/hv_snapshot.c
@@ -331,6 +331,16 @@ static void vss_on_reset(void)
 int
 hv_vss_init(struct hv_util_service *srv)
 {
+	switch (vmbus_proto_version) {
+		case VERSION_WS2008:
+		case VERSION_WIN7:
+		case VERSION_WIN8:
+			pr_warn("Integration service 'Backup (volume snapshot)'"
+				" not supported on this host version.\n");
+			return -ENOTSUPP;
+		default:
+			break;
+	}
 	recv_buffer = srv->recv_buffer;
 
 	/*