Drivers: hv: vss: full handshake support

Introduce VSS_OP_REGISTER1 to support kernel replying to the negotiation
message with its own version.

Signed-off-by: Vitaly Kuznetsov <[e-mail]>
Tested-by: Alex Ng <[e-mail]>
Signed-off-by: K. Y. Srinivasan <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/hv/hv_snapshot.c

···
 
 static void vss_respond_to_host(int error);
 
+/*
+ * This state maintains the version number registered by the daemon.
+ */
+static int dm_reg_value;
+
 static const char vss_devname[] = "vmbus/hv_vss";
 static __u8 *recv_buffer;
 static struct hvutil_transport *hvt;
···
 			hv_vss_onchannelcallback);
 }
 
+static int vss_handle_handshake(struct hv_vss_msg *vss_msg)
+{
+	u32 our_ver = VSS_OP_REGISTER1;
+
+	switch (vss_msg->vss_hdr.operation) {
+	case VSS_OP_REGISTER:
+		/* Daemon doesn't expect us to reply */
+		dm_reg_value = VSS_OP_REGISTER;
+		break;
+	case VSS_OP_REGISTER1:
+		/* Daemon expects us to reply with our own version*/
+		if (hvutil_transport_send(hvt, &our_ver, sizeof(our_ver)))
+			return -EFAULT;
+		dm_reg_value = VSS_OP_REGISTER1;
+		break;
+	default:
+		return -EINVAL;
+	}
+	vss_transaction.state = HVUTIL_READY;
+	pr_info("VSS daemon registered\n");
+	return 0;
+}
+
 static int vss_on_msg(void *msg, int len)
 {
 	struct hv_vss_msg *vss_msg = (struct hv_vss_msg *)msg;
···
 	if (len != sizeof(*vss_msg))
 		return -EINVAL;
 
-	/*
-	 * Don't process registration messages if we're in the middle of
-	 * a transaction processing.
-	 */
-	if (vss_transaction.state > HVUTIL_READY &&
-	    vss_msg->vss_hdr.operation == VSS_OP_REGISTER)
-		return -EINVAL;
-
-	if (vss_transaction.state == HVUTIL_DEVICE_INIT &&
-	    vss_msg->vss_hdr.operation == VSS_OP_REGISTER) {
-		pr_info("VSS daemon registered\n");
-		vss_transaction.state = HVUTIL_READY;
+	if (vss_msg->vss_hdr.operation == VSS_OP_REGISTER ||
+	    vss_msg->vss_hdr.operation == VSS_OP_REGISTER1) {
+		/*
+		 * Don't process registration messages if we're in the middle
+		 * of a transaction processing.
+		 */
+		if (vss_transaction.state > HVUTIL_READY)
+			return -EINVAL;
+		return vss_handle_handshake(vss_msg);
 	} else if (vss_transaction.state == HVUTIL_USERSPACE_REQ) {
 		vss_transaction.state = HVUTIL_USERSPACE_RECV;
 		if (cancel_delayed_work_sync(&vss_timeout_work)) {

include/uapi/linux/hyperv.h

···
 
 #define VSS_OP_REGISTER 128
 
+/*
+  Daemon code with full handshake support.
+ */
+#define VSS_OP_REGISTER1 129
+
 enum hv_vss_op {
 	VSS_OP_CREATE = 0,
 	VSS_OP_DELETE,

tools/hv/hv_vss_daemon.c

···
 	int	op;
 	struct hv_vss_msg vss_msg[1];
 	int daemonize = 1, long_index = 0, opt;
+	int in_handshake = 1;
+	__u32 kernel_modver;
 
 	static struct option long_options[] = {
 		{"help",	no_argument,	   0,  'h' },
···
 		}
 
 		len = read(vss_fd, vss_msg, sizeof(struct hv_vss_msg));
+
+		if (in_handshake) {
+			if (len != sizeof(kernel_modver)) {
+				syslog(LOG_ERR, "invalid version negotiation");
+				exit(EXIT_FAILURE);
+			}
+			kernel_modver = *(__u32 *)vss_msg;
+			in_handshake = 0;
+			syslog(LOG_INFO, "VSS: kernel module version: %d",
+			       kernel_modver);
+			continue;
+		}
 
 		if (len != sizeof(struct hv_vss_msg)) {
 			syslog(LOG_ERR, "read failed; error:%d %s",