First, the crypto request completion handler contains a bug in that it
fails to reset fs_done correctly after the request is completed.  This
is only a problem for asynchronous drivers.  Second, some hardware
drivers have input constraints which ZFS does not satisfy.  For
instance, ccp(4) apparently requires the AAD length for AES-GCM to be a
multiple of the cipher block size, and with qat(4) the AES-GCM AAD
length may not be longer than 240 bytes.  FreeBSD's generic crypto
framework doesn't have a mechanism to automatically fall back to a
software implementation if a hardware driver cannot process a request,
and ZFS does not tolerate such errors.