Drivers: hv: util: introduce state machine for util drivers

KVP/VSS/FCOPY drivers work in fully serialized mode: we wait till userspace
daemon registers, wait for a message from the host, send this message to the
daemon, get the reply, send it back to host, wait for another message.
Introduce enum hvutil_device_state to represend this state in all 3 drivers.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Tested-by: Alex Ng <alexng@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/hyperv_vmbus.h

@@ -755,4 +755,13 @@ static inline void hv_poll_channel(struct vmbus_channel *channel,
 		cb(channel);
 }
 
+enum hvutil_device_state {
+	HVUTIL_DEVICE_INIT = 0,  /* driver is loaded, waiting for userspace */
+	HVUTIL_READY,            /* userspace is registered */
+	HVUTIL_HOSTMSG_RECEIVED, /* message from the host was received */
+	HVUTIL_USERSPACE_REQ,    /* request to userspace was sent */
+	HVUTIL_USERSPACE_RECV,   /* reply from userspace was received */
+	HVUTIL_DEVICE_DYING,     /* driver unload is in progress */
+};
+
 #endif /* _HYPERV_VMBUS_H */