DNODE_FLAG_USED_BYTES
#define DN_USED_BYTES(dnp) (((dnp)->dn_flags & DNODE_FLAG_USED_BYTES) ? \
dnode->dn_flags = DNODE_FLAG_USED_BYTES;
dnode->dn_flags = DNODE_FLAG_USED_BYTES;
assert((dnode->dn_flags & DNODE_FLAG_USED_BYTES) != 0);