cannot access dataset system/usr/home: Operation not supported
by including libzfs_impl.h. What libzfs_impl.h does is to redefine ioctl() to
be compatible with OpenSolaris. More specifically OpenSolaris returns ENOMEM
when buffer is too small and sets field zc_nvlist_dst_size to the size that
will be big enough for the data. In FreeBSD case ioctl() doesn't copy data
structure back in case of a failure. We work-around it in kernel and libzfs by
returning 0 from ioctl() and always checking if zc_nvlist_dst_size hasn't
changed. For this work-around to work in pyzfs we need this compatible ioctl()
which is implemented in libzfs_impl.h.
MFC after: 2 weeks
0926b8ce7c