if those are the only fields you'd like to export, then yea.
but you must include the exact syntax of the xml, best including: <exported>true</exported> for each field.
like this:
<field>
<exported>true</exported><origName>src</origName><dstName>src</dstName>
</field>
See full fieldMapping.xml example for guide usage
<?xml version="1.0" encoding="utf-8"?>
<fields>
<!-- field names/types of tables/fields can be found in fw.lf file -->
<field>
<exported>true</exported><!-- optional, field that is not exported won't be sent / by default it's true-->
<origName>time</origName><!-- field name in the log, can be different between joined and not joined log -->
<dstName>start</dstName><!-- the field will be exported with this name -->
<required>true</required><!-- optional, traffic without this field is dropped/default is false-->
</field>
<field>
<origName>src</origName>
<dstName>cef_src</dstName>
</field>
<field>
<origName>dst</origName>
<dstName>cef_dst</dstName>
</field>
<table>
<tableName>match_table</tableName><!-- name of the table/ field of the table is changed during join, see log_unification_scheme.C -->
<tableFormat></tableFormat><!-- optional, the format of table export, by default flat-->
<exported>true</exported><!-- optional, field that is not exported won't be sent / by default it's true-->
<required>false</required><!-- optional, traffic without this field is dropped/default is false-->
<fields>
<field>
<origName>layer_name</origName>
<dstName>cef_layer_name</dstName>
</field>
</fields>
</table>