NC_NLEN_MASK
CTASSERT(NC_NLEN_MASK >= MAXPATHLEN);
int cache_maxlen __read_mostly = NC_NLEN_MASK; /* max name length to cache */
KASSERT((nlen & ~NC_NLEN_MASK) == 0);
#define NC_NLEN(ncp) ((ncp)->nc_key & NC_NLEN_MASK)