VtDataRoot returns $VTDATAROOT or the default if $VTDATAROOT is not set.

VtMysqlBaseDir returns the Mysql base directory, which contains the fill_help_tables.sql script for instance.

VtMysqlRoot returns the root for the mysql distribution, which contains bin/mysql CLI for instance.

VtRoot returns $VTROOT or tries to guess its value if it's not set.

DefaultVtDataRoot is the default value for VTROOT environment variable.

DefaultVtRoot is only required for hooks.