Va. Code § 19.2-332
Whenever in a criminal case an officer or other person renders any service required by law for which no specific compensation is provided, or whenever any other service has been rendered pursuant to the request or prior approval of the court, the court shall allow therefor such sum as it deems reasonable, including mileage at a rate provided by law, and such allowance shall be paid out of the state treasury from the appropriation for criminal charges on the certificate of the court stating the nature of the service. This section shall not prevent any payment under § 2.2-816, which could have been made if this section had not been enacted.
This section shall not be construed to authorize the payment of any additional compensation to an officer or other employee of the Commonwealth who is compensated for his services exclusively by salary unless it be otherwise expressly provided by law.
Va. Code § 19.2-332