dovecot - Oct 2015 - iterate users with passwd-file passdb?

Apologies for the basic question, but I've been googling and can't
figure out if this is possible or not.

Simply: Is it possible to iterate over users if I'm using the
passwd-file passdb driver? Do I need a SQL-based driver if I want to
iterate?

Here's what I've got right now. I don't have many users, and would
prefer to retain the simplicity of the passwd-file if possible.

Thanks!


passdb {
    driver = passwd-file
    args = username_format=%u scheme=ssha512 /etc/dovecot/passwd.db
    deny = no
    master = no
    pass = no
    skip = never
    result_failure = continue
    result_internalfail = continue
    result_success = return-ok
}

userdb {
    driver = static
    args = uid=5000 gid=5000 home=/var/mail/vmail/%d/%n
}