Constant DM_NAME_PREFIX 

pub const DM_NAME_PREFIX: &'static str;

Device-mapper name prefix for sandbox snapshots.

Public with COW_FILE_PREFIX and COW_FILE_SUFFIX because the convention has an inverse: CowManager::reconcile_stale reads an owner back out of a name on the host, and a composer holding a durable record it cannot otherwise interpret does the same to decide what that record still names. One definition, so the two directions cannot drift.