Restarting a driver?

[Gilles]

Hello

Out of curiosity, why can't I restart the Zaptel driver that is used
by Asterisk to communicate with a PCI telephony card?

# /usr/local/etc/rc.d/zaptel restart

 zaptelkldunload: can't find file wcte12xp.ko: No such file or
directory
kldunload: can't find file wcte11xp.ko: No such file or directory
kldunload: can't find file wct4xxp.ko: No such file or directory
kldunload: can't find file wct1xxp.ko: No such file or directory
kldunload: can't unload file: Device busy
kldunload: can't find file wcfxo.ko: No such file or directory
kldunload: can't find file tau32pci.ko: No such file or directory
kldunload: can't find file qozap.ko: No such file or directory
kldunload: can't unload file: Device busy
 zaptelkldload: can't load /usr/local/lib/zaptel/zaptel.ko: File
exists

# tail /var/log/messages
[...]
 Jun 20 12:34:42 freebsd kernel: kldunload: attempt to unload file
that was loaded by the kernel

Do some device drivers require using special commands to
unload/reload?

Thank you.