vq_t
#define insque(e, p) ((vq_t *)(e))->back = (caddr_t)(p); \
((vq_t *)(e))->fwd = \
(caddr_t)((vq_t *)((vq_t *)(p))->fwd); \
((vq_t *)((vq_t *)(p))->fwd)->back = (caddr_t)(e); \
((vq_t *)(p))->fwd = (caddr_t)(e);
#define remque(e) ((vq_t *)((vq_t *)(e))->back)->fwd = \
(caddr_t)((vq_t *)(e))->fwd; \
((vq_t *)((vq_t *)(e))->fwd)->back = \
(caddr_t)((vq_t *)(e))->back; \
((vq_t *)(e))->fwd = NULL; \
((vq_t *)(e))->back = NULL;