Add check before adding vsn to pvm instance

Author: Alexander-Kita

ibm/service/power/resource_ibm_pi_virtual_serial_number.go

@@ -83,20 +83,21 @@ func resourceIBMPIVirtualSerialNumberCreate(ctx context.Context, d *schema.Resou
 	}
 
 	serialString := ""
+	oldPvmInstanceId := ""
 	if vsnArg != AutoAssign {
 		vsn, err := client.Get(vsnArg)
 		if err != nil {
 			return diag.FromErr(err)
 		}
+		oldPvmInstanceId = *vsn.PvmInstanceID
 		if v, ok := d.GetOk(Arg_Description); ok {
 			description := v.(string)
 			if description != *vsn.Description {
-				pvmInstanceId := *vsn.PvmInstanceID
-				if pvmInstanceId != "" {
+				if oldPvmInstanceId != "" {
 					updateBody := &models.UpdateServerVirtualSerialNumber{
 						Description: &description,
 					}
-					_, err := client.PVMInstanceUpdateVSN(pvmInstanceId, updateBody)
+					_, err := client.PVMInstanceUpdateVSN(oldPvmInstanceId, updateBody)
 					if err != nil {
 						return diag.FromErr(err)
 					}
@@ -116,6 +117,9 @@ func resourceIBMPIVirtualSerialNumberCreate(ctx context.Context, d *schema.Resou
 
 	if pvmInstanceId, ok := d.GetOk(Arg_PVMInstanceId); ok {
 		pvmInstanceIdArg := pvmInstanceId.(string)
+		if oldPvmInstanceId != "" && pvmInstanceIdArg != oldPvmInstanceId {
+			return diag.Errorf("please detach virtual serial number from current pvm instance before specifying %s in creation", Arg_PVMInstanceId)
+		}
 		instanceClient := instance.NewIBMPIInstanceClient(ctx, sess, cloudInstanceID)
 		restartInstance, err := stopLparForVSNChange(ctx, instanceClient, pvmInstanceIdArg, d.Timeout(schema.TimeoutCreate))
 		if err != nil {
@@ -127,8 +131,7 @@ func resourceIBMPIVirtualSerialNumberCreate(ctx context.Context, d *schema.Resou
 			Serial: &serialNumber,
 		}
 		if v, ok := d.GetOk(Arg_Description); ok {
-			description := v.(string)
-			addBody.Description = description
+			addBody.Description = v.(string)
 		}
 		err = client.PVMInstanceAttachVSN(pvmInstanceIdArg, addBody)
 		if err != nil {