The idea is to abstract over the users that kamid manages. The virtual table allows to use a custom userbase instead of the local UNIX users. The userdata tables maps (virtual) users to their home directory, which is the only directory tree exported by kamid as of now. Together, they allow a powerful and flexible management of the users and their data. The idea is somewhat stolen from smtpd(8).

it doesn't set errno when fails to find a user (which is correct, since a missing user is not *technically* an error, but still...)

STAILQ_* macros seems to be more widespread than SIMPLEQ_*